Browsing by Author "Cao, Fong-Yi"

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2-Dimensional cross-shaped tetrathienonaphthalene-based ladder-type acceptor for high-efficiency organic solar cells
(2020-06-28)
Chang, Shao-Ling
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Cao, Fong-Yi
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Huang, Kuo-Hsiu
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Lee, Wei-Liang
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Lee, Meng-Hsun
AnNC-FICnonfullerene acceptor, using a didodecylnaphthodithiophene (NDT) embedded octacyclic ladder-type donorNC, had been described previously. In this work, a new cross-shapedTC-FICnonfullerene acceptor is designed by substitution of the NDT unit in theNCskeleton with a 2-dimensional didodecyltetrathienonaphthalene (TTN) unit. The 2-dimensionalTC pi-system with two vertically fused thiophenes strengthens the electron-donating ability, promotes pi-electron delocalization and enhances intramolecular donor-acceptor charge transfer and intermolecular pi-pi interactions. As a result,TC-FICshows more red-shifted and widened absorption compared to theNC-FICcounterpart. The PBDB-T:TC-FICdevice exhibits a higher efficiency of 11.6% which greatly outperformed the corresponding PBDB-T:NC-FICdevice with an efficiency of 7.52%. The dramatic 54% enhancement in efficiency is ascribed to the improved light-harvesting ability and enhanced charge mobilities which are benefited from the central 2-dimensionalTTNmoiety. By incorporatingPC(71)BMto improve absorption and electron transport, the ternary-blend PBDB-T : TC-FIC : PC(71)BMdevice (1 : 1 : 1 in wt%) achieves a highest PCE of 13.49% with an enhancedJ(sc)of 23.80 mA cm(-2), an FF of 64.4%, and aV(oc)of 0.88 V.
Alternating Copolymers Incorporating Cyclopenta[2,1-b:3,4-b ']dithiophene Unit and Organic Dyes for Photovoltaic Applications
(2011-04-15)
Cheng, Yen-Ju
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Hung, Lung-Chang
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Cao, Fong-Yi
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Kao, Wei-Shun
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Chang, Chih-Yu
We have synthesized six p-type copolymers, CPDT-co-TPADCN, CPDT-co-TPADTA, CPDT-co-TPATCN, CPDT-coDFADCN, CPDT-co-DFADTA, and CPDT-co-DFATCN, consisting of a cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) unit and an organic dye in an alternating arrangement. Triphenylamine (TPA) or difluorenylphenyl amine (DFA) units serve as the electron donors, whereas dicyanovinyl (DCN), 1,3-diethyl-2-thiobarbituric acid, or tricyanovinyl (TCN) units act as the electron acceptors in the dyes. The target polymers were prepared via Stille coupling, followed by postfunctionalization to introduce the electron acceptors to the side chains. Because of the strongest withdrawing ability of TCN acceptor to induce efficient intramolecular charge transfer, CPDT-co-TPATCN and CPDT-co-DFATCN exhibit the broader absorption spectra covering from 400 to 900 nm and the narrower optical band gaps of 1.34 eV. However, the CPDT-co-TPATCN:PC(71)BM and CPDT-co-DFATCN:PC(71)BM based solar cells showed the power conversion efficiencies (PCEs) of 0.22 and 0.31%, respectively, due to the inefficient exciton dissociation. The DFA-based polymers possess deeper-lying HOMO energy levels than the TPA-based polymer analogues, leading to the higher V(oc) values and better efficiencies. The device based on CPDT-co-DFADTA:PC(71)BM blend achieved the best PCE of 1.38% with a V(oc) of 0.7 V, a J(sc) of 4.57 mA/cm(2), and a fill factor of 0.43. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49:1791-1801, 2011
Angular-Shaped 4,9-Dialkylnaphthodithiophene-Based Donor-Acceptor Copolymers for Efficient Polymer Solar Cells and High-Mobility Field-Effect Transistors
(2015-04-14)
Cheng, Sheng-Wen
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Tsai, Che-En
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Liang, Wei-Wei
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Chen, Yung-Lung
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Cao, Fong-Yi
Although the tetracyclic angular-shaped naphthodithiophenes (aNDTs) derivatives are an emergent building block for constructing promising semiconductor conjugated polymers, the absence of aliphatic side chains as solubilizing groups on the aNDTs greatly restricted their further application toward polymer synthesis. To create a new class of aNDT-based polymers for widespread applications in solution-processable OFETs and PSCs, side-chain engineering of the aNDT-based structures plays a pivotal role in improving solubility and optimizing electronic/steric properties associated with the resultant solar cell characteristics. In this research, we developed an efficient and straightforward methodology to construct the angular naphthodithophene core with regiospecific introduction of two aliphatic chains at its 4,9-positions via a base-induced double 6p-cyclization. For the first time, the corresponding 2,7-distannylated-4,9-dialkylated aNDT monomers were polymerized with FBT and DPP acceptors to make two new PaNDTDTFBT and PaNDTDPP donor-acceptor copolymers. The photovoltaic devices based on the PaNDTDTFBT:PC71BM blend not only showed a promising PCE of 6.52% with conventional configuration but also achieved a higher PCE of 6.86% with inverted configuration. Moreover, PaNDTDPP with strong intermolecular interaction achieved a high FET hole mobility of 0.202 cm(2) V-1 s(-1).
Angular-Shaped 4,9-Dialkylnaphthodithiophene-Based Octacyclic Ladder-Type Non-Fullerene Acceptors for High Efficiency Ternary-Blend Organic Photovoltaics
(2018-08-14)
Cao, Fong-Yi
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Huang, Wen-Chia
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Chang, Shao-Ling
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Cheng, Yen-Ju
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應用化學系
An angular-shaped 4,9-didodecylnaphthodithiophene-based octacyclic ladder-type structure was developed. This new ladder-type donor (LD) was coupled with electron withdrawing IC and FIC units to form two A-LD-A type non-fullerene acceptor materials, NCIC and NCFIC. NCIC and NCFIC as the n-type acceptors are blended with a p-type donor PBDB-T to form the complementary absorption and suitable energy level alignments. The binary-blend PBDB-T:NCIC and PBDB-T:NCFIC devices achieved an efficiency of 7.3% and 7.5%, respectively. PC71BM was incorporated to form D-1:A(1):A(2) ternary blends which further strengthen the absorption at shorter wavelengths. Introduction of PC71BM not only efficiently improves the absorption but also provides multiple channels for exciton dissociation and electron transport to dramatically improve J(sc). It is interesting to find that the V-oc of the ternary-blend devices is reversely in proportional to the added amount of PC71BM. The device using the PBDB-T:NCIC:PC71BM (1:1:1 in wt %) showed an improved PCE of 8.32%. Moreover, the optimized device using the PBDB-T:NCFIC:PC71BM (1:1:1.5 in wt %) blend achieved the highest efficiency of 9.18%.
Bispentafluorophenyl-Containing Additive: Enhancing Efficiency and Morphological Stability of Polymer Solar Cells via Hand-Grabbing-Like Supramolecular Pentafluorophenyl-Fullerene Interactions
(2017-12-20)
Hung, Kai-En
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Tsai, Che-En
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Chang, Shao-Ling
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Lai, Yu-Ying
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Jeng, U-Ser
A new class of additive materials bis(pentafluorophenyl) diesters (BFEs) where the two pentafluorophenyl (C6F5) moieties are attached at the both ends of a linear aliphatic chain with tunable tether lengths (BFS, BF7, and BF13) were designed and synthesized. In the presence of BF7 to restrict the migration of fullerehe by hand-grabbing-like supramolecular interactions induced between the C6F5 groups and the surface of fullerene, the P3HT:PC61BM:BF7 device showed stable device characteristiCs after thermal heating at 150 degrees C for 25, 'IL The morphologies Of the active layers were systematically investigated by optical microscopy, grazing-incidence small-angle X-ray scattering (GISAXS), and atomic force microscopy. The tether length between the two C6F5 groups plays a pivotal role in controlling the intermolecular attractions. BF13 with a long and flexible tether might form a BF13-fullerene sandwich complex that fails to prevent fullerene's movement and aggregation, while BF5 with too short tether length decreases the possibility of interactions between the C6F5 groups and the fullerenes. BF7 with the optimal tether length has the best ability to stabilize the morphology. In sharp contrast, the nonfluorinated BP7 analogue without C6F5-C-60 physical interactions does not have the capability of morphological stabilization, unambiguously revealing the necessity of the C6F5 group. Most importantly, the function of BF7 can be also applied to the high-performance PffBT4BT-20D:PC71BM system, which exhibited an original PCE of 8.80%. After thermal heating at 85 degrees C for 200 h, the efficiency of the Pffi3T4BT-20D:PC71BM:BF7 device only decreased slightly to 7.73%, maintaining 88% of its original efficiency. To the best of our knowledge, this is the first time that the thermabdriven morphological evolution of the high-performance PffBT4BT-20D polymer has been investigated, and its morphological stability in the inverted device can be successfully preserved by the incorporation of BF7. This research also demonstrates that BF7 is not only effective with PC61BM but also to PC71BM.
Compact Bis-Adduct Fullerenes and Additive-Assisted Morphological Optimization for Efficient Organic Photovoltaics
(2014-11-26)
Lai, Yun-Yu
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Liao, Ming-Hung
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Chen, Yen-Ting
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Cao, Fong-Yi
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Hsu, Chain-Shu
Bis-adduct fullerenes surrounded by two insulating addends sterically attenuate intermolecular interaction and cause inferior electron transportation. In this research, we have designed and synthesized a new class of bis-adduct fullerene materials, methylphenylmethano-C-60 bis-adduct (MPC(60)BA), methylthienylmethano-C-60 bis-adduct (MTC(60)BA), methylphenylmethano-C-70 bis-adduct (MPC(70)BA), and methylthienylmethano-C-70 bis-adduct (MTC(70)BA), functionalized with two compact phenylmethylmethano and thienylmethylmethano addends via cyclopropyl linkages. These materials with much higher-lying lowest unoccupied molecular orbital (LUMO) energy levels successfully enhanced the V-oc values of the P3HT-based solar cell devices. The compact phenylmethylmethano and thienylmethylmethano addends to promote fullerene intermolecular interactions result in aggregation-induced phase separation as observed by the atomic force microscopy (AFM) and transmission electron microscopy (TEM) images of the poly(3-hexylthiophene-2,5-diyl) (P3HT)/bis-adduct fullerene thin films. The device based on the P3HT/MTC(60)BA blend yielded a V-oc of 0.72 V, a J(sc) of 5.87 mA/cm(2), and a fill factor (FF) of 65.3%, resulting in a power conversion efficiency (PCE) of 2.76%. The unfavorable morphologies can be optimized by introducing a solvent additive to fine-tune the intermolecular interactions. 1-Chloronaphthalene (CN) having better ability to dissolve the bis-adduct fullerenes can homogeneously disperse the fullerene materials into the P3HT matrix. Consequently, the aggregated fullerene domains can be alleviated to reach a favorable morphology. With the assistance of CN additive, the P3HT/MTC(60)BA-based device exhibited enhanced characteristics (a V-oc of 0.78 V, a J(sc) of 9.04 mA/cm(2), and an FF of 69.8%), yielding a much higher PCE of 4.92%. More importantly, the additive-assisted morphological optimization is consistently effective to all four compact bis-adduct fullerenes regardless of the methylphenylmethano or methylthienylmethano scaffolds as well as C-60 or C-70 core structures. Through the extrinsic additive treatment, these bis-adduct fullerene materials with compact architectures show promise for high-performance polymer solar cells.
Forced coplanarity of dithienofluorene-based non-fullerene acceptors to achieve high-efficiency organic solar cells
(2019-08-14)
Cao, Fong-Yi
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Huang, Po-Kai
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Su, Yen-Chen
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Huang, Wen-Chia
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Chang, Shao-Ling
Ladder-type structures have been the key element for high performance non-fullerene acceptors (NFAs). In this work, two dithieno[3,2-b:6,7-b ']fluorine (DTF)-based nonfullerene acceptors, non-bridged DTFT5-FIC and carbon-bridged DTFT9-FIC, with an identical conjugated backbone were designed and synthesized for investigation of the planarization effect. The chemical rigidification with forced coplanarity indeed plays a pivotal role in determining the molecular properties. Compared to the non-bridged open-chain DTFT5-FIC counterpart, the nonacyclic ladder-type DTFT9-FIC with a fully planarized backbone exhibits higher thermal stability, bathochromic absorption and higher electron mobility. The devices using PBDB-T as the p-type polymer and fully planar DTFT9-FIC as the acceptor showed a high efficiency of 9.58%, which is superior to that of the device using the partially planar DTFT5-FIC material (5.45%). By incorporating PC71BM as the second acceptor to enhance the absorption at shorter wavelengths, optimize the morphology and facilitate electron transport, the ternary-blend device using PBDB-T:DTFT9-FIC:PC71BM achieved the highest PCE of 11.82% with a V-oc of 0.88 V, a higher J(sc) of 20.59 mA cm(-2), and an FF of 65.27%.
Highly Efficient Inverted D:A(1):A(2) Ternary Blend Organic Photovoltaics Combining a Ladder-type Non-Fullerene Acceptor and a Fullerene Acceptor
(2017-07-26)
Chang, Shao-Ling
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Cao, Fong-Yi
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Huang, Wen-Chia
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Huang, Po-Kai
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Hsu, Chain-Shu
A formylated benzodi(cyclopentadithiophene) (BD CPDT) ladder-type structure with forced coplanarity is coupled with two 1,1-dicyanomethylene-3-indanone (IC) moieties via olefination to form a non-fullerene acceptor, BDCPDT-IC. The BDCPDT-IC, as an acceptor (A(1)) with broad light-absorbing ability and excellent solution processability, is combined with a second PC71BM acceptor (A(2)) and a medium band gap polymer, PBDB-T, as the donor (D) to form a ternary blend with gradient HOMO/LUMO energy alignments and panchromatic absorption. The device with the inverted architecture using the D:A(1):A(2) ternary blend has achieved a highest efficiency of 9.79% with a superior J(sc) of 16.84 mA cm(-2).
Isomeric effect of fluorene-based fused-ring electron acceptors to achieve high-efficiency organic solar cells
(2020-03-14)
Xue, Yung-Jing
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Cao, Fong-Yi
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Huang, Po-Kai
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Su, Yen-Chen
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Cheng, Yen-Ju
Acceptor-donor-acceptor (A-D-A) non-fullerene electron acceptors (NFEAs) using ladder-type donor structures have become the dominant n-type materials for achieving high-efficiency OSCs. In this work, two isomeric fluorene-based ladder-type structures FCTT (TT-C-F-C-TT) and FTCT (T-C-TFT-C-T) have been designed and synthesized. These two isomeric donors with the different fused-ring arrangement, molecular geometry, and side-chain placement were end-capped with the FIC acceptors to form two NFEAs FCTT-FIC and FTCT-FIC isomeric materials. Compared to FTCT-FIC using the thiophene (T)-terminal donor, FCTT-FIC with the thienothiophene (TT)-terminal donor has more evenly distributed side chains on both sides of the backbone and less steric hindrance near the FIC acceptors, which enables stronger antiparallel pi-pi packing among the end-groups to create a channel for efficient electron transport, as evidenced by the thin-film GIWAXS measurements. FCTT-FIC displayed a larger optical bandgap and deeper-lying energy levels than its FTCT-FIC isomer. Compared to the PBDB-T:FTCT-FIC device, the PBDB-T:FCTT-FIC device showed a higher PCE of 10.32% with an enhanced J(sc) of 19.63 mA cm(-2) and an FF of 69.14%. A PM6:FCTT-FIC device using PM6 as a p-type polymer achieved the highest PCE of 12.23%. By introducing PC71BM as the second acceptor to enhance the absorption at shorter wavelengths, optimize the morphology and facilitate electron transport, the ternary-blend PM6:FCTT-FIC:PC71BM (1 : 1 : 0.5 in wt%) device yielded the highest PCE of 13.37% with a V-oc of 0.92 V, a higher J(sc) of 19.86 mA cm(-2), and an FF of 73.2%. This result demonstrated that the TT-terminal ladder-type donor is generally a better molecular design than the corresponding T-terminal ladder-type isomer for the development of new A-D-A NFEAs.
Isomerically Pure Benzothiophene-Incorporated Acceptor: Achieving Improved V-oc and J(sc) of Nonfullerene Organic Solar Cells via End Group Manipulation
(2019-09-11)
Chang, Shao-Ling
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Hung, Kai-En
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Cao, Fong-Yi
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Huang, Kuo-Hsiu
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Hsu, Chain-Shu
Benzene-based 1,1-dicyanomethylene-3-indanone (IC) derivatives have been widely utilized as the end-group to construct acceptor-donor-acceptor type nonfullerene acceptors (A-D-A type NFAs). The extension of the end-group conjugation of nonfullerene acceptors (NFAs) is a rational strategy to facilitate intermolecular stacking of the end-groups which are responsible for efficient electron transportation. A bicyclic benzothiophene-based end-group acceptor, 2-(3-oxo-2,3-dihydro-1H-benzo[b]cyclopenta[d]thiophen-1-ylidene)malononitrile, denoted as alpha-BC was designed and synthesized. The Knoevenagel condensation of the unsymmetrical 1,3-diketo-precursor with one equivalent of malononitrile selectively reacts with the keto group attached at the alpha-position of the thiophene unit, leading to the isomerically pure benzothiophene-fused alpha-BC. The well-defined alpha-BC with extended conjugation was condensed with three different ladder-type diformylated donors to form three new A-D-A NFAs named BDCPDT-BC, DTCC-BC, and ITBC, respectively. The corresponding IC-based BDCPDT-IC, DTCC-IC, and ITIC model compounds were also synthesized for comparison. The incorporation of the electron-rich benzothiophene unit in the end-group upshifts the lowest unoccupied molecular orbital energy levels of the NFAs, which beneficially enlarges the V-oc values. On the other hand, the benzothiophene unit in alpha-BC not also imparts an optical transition in the shorter wavelengths around 340-400 nm for a better light harvesting ability but also promotes the antiparallel pi-pi stacking of the end-groups for efficient electron transport. The organic photovoltaic cell devices using a PBDB-T polymer and BC-based NFAs all showed the improved V-oc and J(sc) values. The BDCPDT-BC- and DTCC-BC-based devices exhibited a power conversion efficiency (PCE) of 10.82 and 10.74%, respectively, which outperformed the corresponding BDCPDT-IC-, and DTCC-IC-based devices (9.33 and 9.25%). More importantly, the ITBC-based device delivered the highest PCE of 12.07% with a J(sc) of 19.90 mA/cm(2), a V-oc of 0.94 V, and an fill factor of 64.51%, representing a 14% improvement relative to the traditional ITIC-based device (10.05%).
Mg Doped CuCrO2 as Efficient Hole Transport Layers for Organic and Perovskite Solar Cells
(2019-09-01)
Zhang, Boya
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Thampy, Sampreetha
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Dunlap-Shohl, Wiley A.
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Xu, Weijie
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Zheng, Yangzi
The electrical and optical properties of the hole transport layer (HTL) are critical for organic and halide perovskite solar cell (OSC and PSC, respectively) performance. In this work, we studied the effect of Mg doping on CuCrO2 (CCO) nanoparticles and their performance as HTLs in OSCs and PSCs. CCO and Mg doped CCO (Mg:CCO) nanoparticles were hydrothermally synthesized. The nanoparticles were characterized by various experimental techniques to study the effect of Mg doping on structural, chemical, morphological, optical, and electronic properties of CCO. We found that Mg doping increases work function and decreases particle size. We demonstrate CCO and Mg:CCO as efficient HTLs in a variety of OSCs, including the first demonstration of a non-fullerene acceptor bulk heterojunction, and CH3NH3PbI3 PSCs. A small improvement of average short-circuit current density with Mg doping was found in all systems.
Morphological Stabilization by Supramolecular Perfl uorophenyl-C-60 Interactions Leading to Effi cient and Thermally Stable Organic Photovoltaics
(2014-03-01)
Liao, Ming-Hung
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Tsai, Che-En
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Lai, Yu-Ying
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Cao, Fong-Yi
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Wu, Jhong-Sian
A new PC61BM-based fullerene, [6,6]-phenyl-C-61 butyric acid pentafluorophenyl ester (PC61BPF) is designed and synthesized. This new n-type material can replace PC61BM to form a P3HT:PC61BPF binary blend or serve as an additive to form a P3HT:PC61BM:PC61BPF ternary blend. Supramolecular attraction between the pentafluorophenyl group of PC61BPF and the C-60 cores of PC61BPF/PC61BM can effectively suppress the PC61BPF/PC61BM materials from severe aggregation. By doping only 8.3 wt% PC61BPF, device PC(61)BP(F)651 exhibits a PCE of 3.88% and decreases slightly to 3.68% after heating for 25 h, preserving 95% of its original value. When PC61BP with non-fluorinated phenyl group is used to substitute PC61BPF, the stabilizing ability disappears completely. The efficiencies of PC(61)BP651 and PC(61)BP321 devices significantly decay to 0.44% and 0.11%, respectively, after 25 h isothermal heating. Most significantly, this strategy is demonstrated to be effective for a blend system incorporating a low band-gap polymer. By adding only 10 wt% PC61BPF, the PDTBCDTB:PC71BM-based device exhibits thermally stable morphology and device characteristics. These findings demonstrate that smart utilization of supramolecular interactions is an effective and practical strategy to control morphological evolution.
Naphthobisthiadiazole-Based Selenophene-Incorporated Quarterchalcogenophene Copolymers for Field-Effect Transistors and Polymer Solar Cells
(2019-03-27)
Cao, Fong-Yi
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Lin, Fang-Yu
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Tseng, Cheng-Chun
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Hung, Kai-En
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Hsu, Jhih-Yang
In this research, we developed six new selenophene-incorporated naphthobisthiadiazole-based donor-acceptor polymers PNT2Th2Se-OD, PNT2Se2Th-OD, PNT4Se-OD, PNT2Th2Se-DT, PNT2Se2Th-DT, and PNT4Se-DT. The structure-property relationships have been systematically established through the comparison of their structural variations: (1) isomeric biselenophene/bithiophene arrangement between PNT2Th2Se and PNT2Se2Th polymers, (2) biselenophene/bithiophene and quarterselenophene donor units between PNT2Th2Se/PNT2Se2Th and PNT4Se polymers, and (3) side-chain modification between the 2-octyldodecylthiophene (OD)- and 2-decyltetradecyl (DT)-series polymers. The incorporation of selenophene units in the copolymers induces stronger charge transfer to improve the light-harvesting capability while maintaining the strong intermolecular interactions to preserve the intrinsic crystallinity for high carrier mobility. The organic field-effect transistor device using PNT2Th2Se-OD achieved a high hole mobility of 0.36 cm(2) V-1 s(-1) with an on/off ratio of 1.9 x 10(5). The solar cells with PNT2Th2Se-OD:PC71BM exhibited a power conversion efficiency of 9.47% with a V-oc of 0.68 V, an fill factor of 67%, and an impressive J(SC), of 20.69 mA cm(-2).
New Thieno[3,2-b]thiophene-Based Acceptor: Tuning Acceptor Strength of Ladder-Type N-Type Materials to Simultaneously Achieve Enhanced V-OC and J(SC) of Nonfullerene Solar Cells
(2018-07-01)
Chang, Shao-Ling
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Cao, Fong-Yi
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Huang, Wen-Chia
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Huang, Po-Kai
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Huang, Kuo-Hsiu
A new thieno[3,2-b]thiophene-incorporated acceptor TTC has been developed. The TTC acceptor was installed in a haptacyclic ladder-type core (BDCPDT) to furnish an n-type BDCPDT-TTC. The standard PBDB-T:BDCPDT-IC device showed a PCE of 9.33% with a V-OC of 0.86 V and a J(SC) of 16.56 mA/cm(2). By molecular engineering of the acceptor unit, the BDCPDT:PBDB-T-based device delivered an enhanced efficiency of 10.29% with a simultaneously enhanced V-OC of 0.94 V and J(SC) of 17.72 mA/cm(2). Incorporation of the electron-donating thieno[3,2-b]thiophene unit into the acceptor moiety decreases the electron accepting strength, thereby upshifting the HOMO/LUMO energy levels to decrease the Delta E-HOMO and E-LOSS achieving a larger Voc. Second, the extended conjugated bicyclic thieno[3,2-b]thiophene ring beneficially induces an additional optical transition at short wavelengths, leading to improvement of J. Alternatively, BDCPDT-FIC installed with the fluorinated acceptor shows more red-shifted absorption to achieve a high J of 19.12 mA/cm(2).
Probing Defect States in Organic Polymers and Bulk Heterojunctions Using Surface Photovoltage Spectroscopy
(2019-05-02)
Murthy, Lakshmi N. S.
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Barrera, Diego
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Xu, Liang
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Gadh, Aakash
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Cao, Fong-Yi
We performed frequency-modulated (AC) and steady-state (DC) surface photovoltage spectroscopy (SPS) measurements on a bilayer structure consisting of an organic semiconductor (P3HT, P3HT:PC61BM, or PFBT2Se2Th:PC71BM) on top of a ZnO electron-transport layer. The AC spectra overlap with the absorption spectra of the organic layer, providing evidence that AC SPS corresponds to band-to-band transitions. The DC spectra are generally broader than the AC spectra, with responses extended below the absorption edge. Thus, DC SPS also probes transitions between band states and trap states within the band gap in addition to band-to-band transitions. When a hole-transport layer (HTL) is deposited on top of the organic layer, the DC spectra of P3HT and P3HT:PC61BM are narrower than those without the HTL, suggesting that the sub-band gap states exist at the surface of these organic semiconductors. In contrast, PFBT2Se2Th:PC71BM does not show signature of surface states or optically active trap states in the band gap. External quantum efficiency and capacitance measurements are employed to explain the nature of sub-band gap states that contribute to surface photovoltage signals and the differences between the two bulk heterojunction systems.
Selenophene-Incorporated Quaterchalcogenophene-Based Donor-Acceptor Copolymers To Achieve Efficient Solar Cells with J(sc) Exceeding 20 mA/cm(2)
(2017-12-12)
Cao, Fong-Yi
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Tseng, Cheng-Chun
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Lin, Fang-Yu
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Chen, Yuzhong
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Yan, He
Three selenophene-incorporated quaterchalcogenophene-based donoracceptor copolymers PFBT2Th2Se, PFBT2Se2Th, and PFBT4Se are designed and synthesized. To systematically fine-tune the molecular properties and investigate the chalcogen effect, PFBT2Th2Se and PFBT2Se2Th hybridize two thiophenes and two selenophenes as the donor with different isomeric main-chain placement while thiophene-free PFBT4Se uses quaterselenophene as the donor. On account of the selenophenes advantageous features such as higher quinoidal population and higher molecular polarizability, the three polymers show good light-harvesting ability, strong intermolecular interactions, high crystallinity, and high charge mobilities. Bulk-heterojunction solar cells incorporating these selenophene-containing polymers have exhibited promising photovoltaic performance with impressive current densities over 20 mA/cm(2). The device with the PFBT2Se2Th:PC71BM blend showed a PCE of 9.02% with a J(sc) of 21.02 mA/cm(2). In addition, the device using quaterselenophene-based PFBT4Se:PC71BM blend exhibited a PCE of 8.92% with a superior J(sc) of 22.63 mA/cm(2) which represents one of the highest current densities from polymer:fullerene-based solar cells reported in the literature.
Self-Assembled and Cross-Linked Fullerene Interlayer on Titanium Oxide for Highly Efficient Inverted Polymer Solar Cells
(2011-03-22)
Cheng, Yen-Ju
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Cao, Fong-Yi
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Lin, Wei-Cheng
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Chen, Chiu-Hsiang
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Hsieh, Chao-Hsiang
We have successfully designed and synthesized two oxetane-functionalized fullerene derivatives, [6,6]-phenyl-C(61)-butyric oxetane ester (PCBO) and [6,6]-phenyl-C(63)-butyric oxetane dendron ester (PCBOD). We demonstrated that the oxetane functionality with neutral nature can anchor onto the TiO(x) surface via cationic ring-opening reaction under thermal and UV treatment, as evidenced by contact angle measurement and X-ray photoelectron spectroscopy. The self-assembly of PCBO, functionalized with one oxetane group, on the TiO(x) surface forms an adhesive monolayer with intimate contact. Inverted bulk-heterojunction device B [ITO/TiO(x)/SA-PCBO/P3HT:PCBM (1:1 w/w)/MoO(3)/Ag, where ITO is indium tin oxide, SA is self-assembled, P3HT is poly(3-hexylthiophene), and PCBM is [6,6]-phenyl-C(61)-butyric acid methyl ester] with this self-assembled PCB (SA-PCBO) modifier showed an impressive power conversion efficiency (PCE) of 4.1%, which outperforms the reference device A (PCE = 3.6%) without this monolayer [ITO/TiO(x)/P3HT:PCBM (1:1 w/w)/MoO(3)/Ag]. This SA-PCBO modifier exerts multipositive effects on the interface, including improvement of exciton dissociation efficiency, reduction of charge recombination, decrease of the interface contact resistance, and passivation of the surface electron traps at the interface of TiO(x). Furthermore, PCBOD, containing two oxetane groups, is capable of self-assembling on the TiO(x) surface and simultaneously undergoing cross-linking, generating a dense, robust, and pinhole-free multimolecular interlayer to further strengthen the interface characteristics. Device C [ITO/TiO(x)/C-PCBOD/P3HT:PCBM(1:1, in wt%)/MoO(3)/Ag] incorporating this cross-linked PCBOD (C-PCBOD) interlayer delivered the highest PCE of 4.5% which represents 26% enhancement over device A. This simple and easy strategy smartly integrates the advantages of self-assembly and cross-linking in a single fullerene-based molecule, showing promise in producing highly efficient inverted PSCs.
Self-assembled tri-, tetra- and penta-ethylene glycols as easy, expedited and universal interfacial cathode-modifiers for inverted polymer solar cells
(2016-06-14)
Cao, Fong-Yi
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Lai, Yu-Ying
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Chen, Yung-Lung
;
Cheng, Yen-Ju
;
應用化學系
Non-conjugated triethylene glycol (3-EG), tetraethylene glycol (4-EG) and pentaethylene glycol (5-EG) are presented as new cathode modification materials to achieve high-performance inverted-PCSs. By spin-coating from a non-chlorinated solvent, these small molecules can self-assemble on ITO via surface coordination and hydrogen bonding to form an ultra-thin layer. Theoretical simulations reveal that the coordination of oxygen atoms in the EG molecules to indium moieties on the ITO surface is the major mechanism in inducing interfacial dipoles, thereby reducing the work function (W-F) of ITO for efficient electron collection. Based on the PBDTTT-EFT:PC71BM blend, the bulk heterojunction device using the 5-EG layer exhibited a higher short-circuit current density (J(sc)) of 15.27 mA cm(-2), fill factor (FF) of 0.69, and power conversion efficiency (PCE) of 8.46%, which are better than those of the corresponding devices using either inorganic ZnO or non-conjugated poly(ethylene oxide) (PEO) as the cathode buffer layer. More importantly, this simple and expedited strategy is also demonstrated to be universally applicable to various p-type conjugated polymers. The EG oligomers with well-defined chemical structures have the advantages of easy availability, simple processability and good device reproducibility, which are crucial keys for future commercialization using large-scale roll-to-roll production.
Synthesis and side-chain isomeric effect of 4,9-/5,10-dialkylated-beta-angular-shaped naphthodithiophenes-based donor-acceptor copolymers for polymer solar cells and field-effect transistors
(2017-04-21)
Chiou, De-Yang
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Cao, Fong-Yi
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Hsu, Jhih-Yang
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Tsai, Che-En
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Lai, Yu-Ying
A systematic methodology is developed to construct the angular-shaped beta-form naphthodithiophene (beta-aNDT) core with regiospecific substitution of two alkyl groups at its 4,9-or 5,10-positions via the base-induced double 6 pi-cyclization of dithienyldieneyne precursors, leading to the two isomeric 4,9-beta-aNDT and 5,10-beta-aNDT monomers. It is found that a more curved geometry of the beta-aNDT units intrinsically increases the solubility and thus the solution-processability of the resultant polymers. Therefore, beta-aNDT units are ideal for polymerization with an acceptor-containing monomer without the need for any solubilizing aliphatic side chains, which are considered the insulating portion that jeopardizes charge transport. Based on this consideration, the 4,9- and 5,10-dialkylated beta-aNDT monomers are polymerized with the non-alkylated DTFBT acceptor to afford two P4,9-beta NDTDTFBT and P5,10-beta NDTDTFBT copolymers for head-to-head comparison of the 4,9-inner/5,10-outer isomeric alkylation effect. It is found that 4,9-beta aNDT adopts a twisted conjugated structure due to the intramolecular steric repulsion between the inner branched side chains and the beta-hydrogens on the thiophene rings. The slightly twisted 4,9-beta-aNDT moiety allows P4,9-beta NDTDTFBT to have higher solubility upon polymerization and thus a higher molecular weight, which eventually induces a higher ordered packing structure in the thin film compared to P5,10-beta NDTDTFBT. As a result, P4,9-beta NDTDTFBT exhibits a higher OFET mobility of 0.18 cm(2) V-1 s(-1), and the P4,9-beta NDTDTFBT: PC71BM-based solar cell device also achieves a higher PCE of 7.23%, which is even better than the corresponding P4,9-alpha NDTDTFBT-based device.
Synthesis of Two-Dimensional Terbenzodithiophene-based Derivative by Palladium-catalyzed C-H Benzannulation and Its Donor-Acceptor Copolymers for Organic Photovoltaics
(2018-01-01)
Cao, Fong-Yi
;
Chen, Yung-Lung
;
Lai, Yu-Ying
;
Cheng, Yen-Ju
;
應用化學系
A new two-dimensional tetrathienyl-TBDT (TBDT-4T) was synthesized by employing palladium-catalyzed C-H benzannulation between an iodobiaryl and 1,2-dithienylacetylene. The stannylated TBDT-4T was copolymerized with di(thiophenyl)difluorobenzothiadiazole (FBT) and fluorothienothiophene (FTT) monomers to yield PTBDT-FBT and PTBDT-FTT, which showed high decomposition temperatures (421 and 408 degrees C) and deep-lying HOMO levels (-5.80 and -5.84 eV). The inverted solar cell device using PTBDT-FBT:PC71BM (1: 1 in wt%) blend showed a power conversion efficiency (PCE) of 4.16%, while the device using PTBDT-FTT:PC71BM (1: 2 in wt%) blend showed a PCE of 3.98%.