Browsing by Author "Gollavelli, Ganesh"

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Interfacial Engineering with Cross-Linkable Fullerene Derivatives for High-Performance Perovskite Solar Cells
(2017-11-08)
Kang, Tin
;
Tsai, Cheng-Min
;
Jiang, Yu-He
;
Gollavelli, Ganesh
;
Mohanta, Nayantara
Two fullerene derivatives with styryl and oxetane cross-linking groups served as interfacial materials to modify an electron-transporting layer (ETL) of TiO2, doped with Au nanoparticles, processed under low-temperature conditions to improve the performance of perovskite solar cells (PSC). The cross-linkable [6,6]-phenyl-C-61-butyric styryl dendron ester was produced via thermal treatment at 160 degrees C for 20 min, whereas the cross-linkable [6,6]-phenyl-C-61-butyric oxetane dendron ester (C-PCBOD) was obtained via UV-curing treatment for 45 s. Both cross-linked fullerenes can passivate surface-trap states of TiO2 and have also excellent surface coverage on the TiO2 layer shown in the corresponding atomic force microscopy images. To improve the crystallinity of perovskite, we propose a simple co-solvent method involving mixing dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) in a specific ratio (DMF/DMSO = 90/10). The fullerene derivative layer between the ETL and perovskite layers significantly improved electron extraction and suppressed charge recombination by decreasing the density of traps at the ETL surface. A planar PSC device was fabricated with the configuration indium tin oxide/TiO2 (Au)/C-PCBOD/perovskite/spiro-OMeTAD/Au to attain a power conversion efficiency (PCE) of 15.9%. The device performance was optimized with C-PCBOD as an interfacial mediate to modify the surface of the mesoporous TiO2 ETL; the C-PCBOD-treated device attained a significantly enhanced performance, PCE 18.3%. Electrochemical impedance spectral and photoluminescence decay measurements were carried out to understand the characteristics of electron transfer and charge recombination of the perovskite/TiO2 samples with and without a fullerene interfacial layer.
Rejuvenation of perovskite solar cells
(2016)
Huang, You
;
Gollavelli, Ganesh
;
Chao, Yi-Hsiang
;
Hsu, Chain-Shu
;
應用化學系
A novel method has been developed to recharge and rejuvenate perovskite solar cells by immersing the device into methyl ammonium iodide (MAI) solution and heating at 70 degrees C for 40 s. We demonstrated that Au electrodes are more robust than Al and Ag electrodes for ZnO planar structures rather than ZnO and TiO2 nanoparticles (NPs). In addition to this, the degradation mechanism of the device has been discussed. The scanning electron microscopy (SEM) images and X-ray diffraction (XRD) spectroscopy are evidence that the perovskite crystals have been regenerated after degradation (60 days) with the help of MAI as a rejuvenating agent. After long-term aging tests with rejuvenation in 185 days, its PCE value is still around 11% compared to the original one of 11.6%.
Synthesis of diketopyrrolopyrrole based conjugated polymers containing thieno[3,2-b]thiophene flanking groups for high performance thin film transistors
(2017-06-14)
Peng, Shih-Hao
;
Tu, Wei-Yi
;
Gollavelli, Ganesh
;
Hsu, Chain-Shu
;
應用化學系
New donor-acceptor (D-A) conjugate polymers based on 3,6-bis(2-bromothieno-[3,2-b] thiophen-5-yl)2,5- bis(2-octyldodecyl) pyrrolo[3,4-c]-pyrrole-1,4-(2H, 5H)-dione (Br-TTDPP) combined with three different electron-donating monomers bithiophene (BT), di(2-thienyl) ethene (TVT), and di(selenophene2- yl) ethene (SVS) were synthesized. The optical band gap, electrochemical properties and organic fieldeffect transistor (OFET) device performance of the TTDPP-based polymers were systematically investigated. X-ray diffraction (XRD) was used to evaluate the molecular packing of the TTDPP-based polymers. Among three polymers, TTDPP-SVS showed the smallest d-spacing and the largest distance of 0.372 for pi-pi stacking. In particular, an OTFT having a TTDPP-SVS active layer showed the highest hole mobility of 0.196 cm(2) V-1 s(-1), the lowest threshold voltage down to -3.6 V, and the highest Ion/Ioff ratio of 6.5 x 10(4). This indicates that p-extended SVS significantly improves charge transport properties.
Thiophene and diketopyrrolopyrrole based conjugated polymers as efficient alternatives to spiro-OMeTAD in perovskite solar cells as hole transporting layers
(2017-06-07)
Peng, Shih-Hao
;
Huang, Tzu-Wei
;
Gollavelli, Ganesh
;
Hsu, Chain-Shu
;
應用化學系
Poly[(5,5 '-bis(3-dodecyl-2-thienyl)-2,2 '-bithiophene)] (PQT), poly-(2,5-bis(3-alkylthiophene-2-yl)thieno-[3,2-b]thiophene) (PBTTT), poly{2,2 '-[(2,5-bis(2-octyldodecyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)]dithiophene-5,5 '-diyl-alt-2,2 '-bithiophene-5,5 '-diyl} (PDQT) and poly{2,2 '-[(2,5-bis(2-octyldodecyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)]dithiophene-5,5 '-diyl-alt-thieno-[3,2-b]thiophene-2,5-diyl} (PDBT-co-TT) were used to replace spiro-OMeTAD as efficient hole transporting layers (HTLs) in perovskite solar cells (PSCs). We demonstrated that both the hole mobility and suitable energy levels of these polymers are important factors in PSCs using organic field-effect transistors (OTFTs) and cyclic voltammetry analysis. The doping effect and the hydrophobic properties of the HTLs were investigated using atomic force microscopy (AFM) and water contact angle measurements. The results show that the PBTTT-14 and PDBT-co-TT based PSCs showed the best PCE of 14.1% and 12.0%, respectively when compared with spiro-OMeTAD based PSCs which have a PCE of 10.2%.