Browsing by Author "Chen, Po-Han"

Now showing 1 - 12 of 12

11%-Efficiency Hybrid Organic/Silicon-Nanowire Heterojunction Solar Cell with an Intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane Layer
(2013)
Tsai, Chia-Ying
;
Chen, Po-Han
;
Huang, Yang-Yue
;
Pen, Huai-Te
;
Yu, Peichen
Hybrid organic-inorganic heterojunction solar cells based on silicon nanowires (SiNWs) are promising candidates for next-generation photovoltaics owing to potentials for low fabrication cost and high efficiency. The SiNW array, fabricated by a simple metal-assisted wet chemical etching method, produces a large surface-area-to-volume ratio, hence allowing efficient light harvesting and charge collection via the formation of a core-sheath p-n junction. However, previously reported power conversion efficiencies (PCEs) are approximately capped at 10%, which is largely depicted by the interface defect densities that limit the open-circuit voltage (V-oc) and fill factor (FF). In this work, we introduce a solution-processed, intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) layer to mitigate the interface recombination loss for hybrid heterojunction solar cells consisted of SiNWs and conjugate polymer poly(3,4-ethylenedioxy-thiophene): poly(styrenesulfonate) (PEDOT:PSS). A record PCE of 11.0% is achieved in contrast to 9.6% from a reference counterpart without TAPC, which represents an enhancement factor of 14.2% ascribed to noticeable improvement in the V-oc and FF. The result is further supported by examining indicators for the interface quality via a suppressed dark saturation current and an enhanced minority carrier lifetime which exhibits an increase from 84 mu sec without TAPC to 87 mu sec with TAPC.
13% Efficiency Hybrid Organic/Silicon-Nanowire Heterojunction Solar Cell via Interface Engineering
(2013-12-01)
Yu, Peichen
;
Tsai, Chia-Ying
;
Chang, Jan-Kai
;
Lai, Chih-Chung
;
Chen, Po-Han
Interface carrier recombination currently hinders the performance of hybrid organic silicon heterojunction solar cells for high-efficiency low-cost photovoltaics. Here, we introduce an intermediate 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAP() layer into hybrid heterojunction solar cells based on silicon nanowires (SINWs) and conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS). The highest power conversion efficiency reaches a record 13.01%, which is largely ascribed to the modified organic surface morphology and suppressed saturation current that boost the open-circuit voltage and fill factor. We show that the insertion of TAP( increases the minority carrier lifetime because of an energy offset at the heterojunction interface. Furthermore, X-ray photoemission spectroscopy reveals that TAP( can effectively block the strong oxidation reaction occurring between PEDOT:PSS and silicon, which improves the device characteristics and assurances for reliability. These learnings point toward future directions for versatile interface engineering techniques for the attainment of highly efficient hybrid photovoltaics.
A Fully Integrated Light-Powering System with Integrated CMOS Photovoltaic Cell for Batteryless IoT Devices
(2019-01-01)
Chen, Po-Han
;
Huang, Chao-Yi
;
Cheng, Hao-Chung
;
Chen, Po-Hung
;
電子工程學系及電子研究所
This paper presents a fully integrated CMOS lightpowering system, integrating CMOS photovoltaic cell and energy harvesting interface, for batteryless internet of things (IoT). The CMOS photovoltaic cell employs deep N-well (DNW) based structure to improve the light-electric conversion efficiency. The energy harvesting interface utilizes a fully integrated two-stage switched-capacitor dc-dc converter to provide an appropriate output voltage for load circuits. It provides 1 V and 0.9 - 1.1 V output under light load and heavy load, respectively. The chip is designed and fabricated by 180-nm CMOS process, without using any off-chip components, except a storage capacitor for testing. The experimental results demonstrate that the proposed 1mm x 2mm fully integrated light-powering system can periodically provide 0.9 V to 1.1 V output voltage to power 1-mA loading circuit. The proposed interface achieves 70 percent peak-efficiency at 1 mu A and higher than 60 percent efficiency over 0.5 mu A to 2 mu A loading currents.
A Fully Integrated Step-Down Switched-Capacitor DC-DC Converter With Dual Output Regulation Mechanisms
(2020-09-01)
Chen, Po-Han
;
Cheng, Hao-Chung
;
Chen, Po-Hung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This letter proposes a fully integrated step-down switched-capacitor (SC) DC-DC converter using 0.18-mu m CMOS technology for system-on-chip applications. The proposed stepdown switched-capacitor DC-DC converter used two control mechanisms: the switch array modulation technique to regulate the output voltage and the voltage ripple modulation technique to adjust the output voltage ripple of the converter as the loading current varied. As a result, the proposed converter could generate a regulated output voltage with low voltage ripple. The converter core performed at conversion ratios of 1/3 and 1/2 under an input voltage of 1.8 V. The measurement results on 180-nm technology showed that the proposed fully integrated step-down switched-capacitor DC-DC converter could achieve a peak power conversion efficiency of 74.1% and maintain power conversion efficiency at levels over 70% within loading ranges between 1.4 and 5 mA. The output voltage ripple was controlled at levels under 63.4 mV within a loading current ranging between 0.1 and 5 mA.
Bandgap Engineering Enhances the Performance of Mixed-Cation Perovskite Materials for Indoor Photovoltaic Applications
(2019-10-01)
Wu, Ming-Ju
;
Kuo, Chien-Chen
;
Jhuang, Lu-Syuan
;
Chen, Po-Han
;
Lai, Yi-Fong
Indoor photovoltaics (IPVs) are attracting renewed interest because they can provide sustainable energy through the recycling of photon energy from household lighting facilities. Herein, the Shockley-Queisser model is used to calculate the upper limits of the power conversion efficiencies (PCEs) of perovskite solar cells (PeSCs) for two types of artificial light sources: fluorescent tubes (FTs) and white light-emitting diodes (WLEDs). An unusual zone is found in which the dependence of the PCEs on the bandgap (E-g) under illumination from the indoor lighting sources follows trends different from that under solar irradiation. In other words, IPVs exhibiting high performance under solar irradiation may not perform well under indoor lighting conditions. Furthermore, the ideal bandgap energy for harvesting photonic power from these indoor lighting sources is approximate to 1.9 eV-a value higher than that of common perovskite materials (e.g., for CH3NH3PbI3). Accordingly, Br- ions are added into the perovskite films to increase their values of E-g. A resulting PeSC featuring a wider bandgap exhibits PCEs of 25.94% and 25.12% under illumination from an FT and a WLED, respectively. Additionally, large-area (4 cm(2)) devices are prepared for which the PCE reaches approximate to 18% under indoor lighting conditions.
Broadband terahertz conductivity and optical transmission of indium-tin-oxide (ITO) nanomaterials
(2013-07-15)
Yang, Chan-Shan
;
Chang, Chan-Ming
;
Chen, Po-Han
;
Yu, Peichen
;
Pan, Ci-Ling
Indium-tin-oxide (ITO) nanorods (NRs) and nanowhiskers (NWhs) were fabricated by an electron-beam glancing-angle deposition (GLAD) system. These nanomaterials are of interests as transparent conducting electrodes in various devices. Two terahertz (THz) time-domain spectrometers (TDS) with combined spectral coverage from 0.15 to 9.00 THz were used. These allow accurate determination of the optical and electrical properties of such ITO nanomaterials in the frequency range from 0.20 to 4.00 THz. Together with Fourier transform infrared spectroscopic (FTIR) measurements, we found that the THz and far-infrared transmittance of these nanomaterials can be as high as 70% up to 15 THz, as opposed to about 9% for sputtered ITO thin films. The complex conductivities of ITO NRs, NWhs as well films are well fitted by the Drude-Smith model. Taking into account that the volume filling factors of both type of nanomaterials are nearly same, mobilities, and DC conductivities of ITO NWhs are higher than those of NRs due to less severe carrier localization effects in the former. On the other hand, mobilities of sputtered ITO thin films are poorer than ITO nanomaterials because of larger concentration of dopant ions in films, which causes stronger carrier scattering. We note further that consideration of the extreme values of Re{sigma} and Im{sigma} as well the inflection points, which are functions of the carrier scattering time (tau) and the expectation value of cosine of the scattering angle (gamma), provide additional criteria for accessing the accuracy of the extraction of electrical parameters of non-Drude-like materials using THz-TDS. Our studies so far indicate ITO NWhs with heights of similar to 1000 nm show outstanding transmittance and good electrical characteristics for applications such as transparent conducting electrodes of THz Devices. (C) 2013 Optical Society of America
Conductive Polymer/GaAs Hybrid Heterojunction Photovoltaic Devices
(2013)
Pan, Huai-Te
;
Huang, Yang-Yue
;
Weng, Wei-Sheng
;
Chen, Po-Han
;
Cheng, Kai-Yuan
Hybrid solar cells combining organic polymers and inorganic semiconductors are extensively investigated recently due to relatively inexpensive cost and simple fabrication processes. In this work, we demonstrate organic/inorganic hybrid heterojunction solar cells based on gallium arsenide (GaAs) substrate and conjugated polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS). First we performed a one-dimensional device simulation based on a self-consistent Poisson and drift-diffusion solver to survey the band alignment between the conductive polymer and GaAs materials and achieve a practical device design. Second, for device fabrication, we prepare a cleaned one-side-polished planar GaAs wafer, followed by thermal evaporation of back-side metal using either Aluminum or titanium/gold as the cathode. Next, PEDOT:PSS is spun-cast onto the wafer and annealed at 115 degrees C for 10 minutes. To improve carrier conduction, we use a self-assembled polystyrene (PS) nanosphere lithography technique to form the sacrificial mask layer, and perform anisotropic metal-assisted chemical etching on GaAs substrates. Various nanostructures such as nanowires or nanorods allow the conformal p-n heterojunction formation at the interface of organic/inorganic semiconductors, which can be beneficial for both light absorption and carrier collection. The optical and electrical characteristics such as reflectance, current voltage, and external quantum efficiency are measured. Currently, we achieve a 3.2% power conversion efficiency with an open-circuit voltage of 0.565 V, short-circuit current of 8.95 mA/cm(2), and a fill factor of 63.29% under a simulated AM1.5G illumination for planar substrates. Device fabrication with GaAs nanowires is still in process and more data will be presented.
High-Transmittance 2 Electrically Tunable Terahertz Phase Shifter with CMOS-Compatible Driving Voltage Enabled by Liquid Crystals
(2019-01-02)
Yang, Chan-Shan
;
Kuo, Chun
;
Chen, Po-Han
;
Wu, Wei-Ta
;
Pan, Ru-Pin
We have investigated tunable terahertz (THz) phase shifters that are based on a sandwiched liquid crystal (LC) cell with indium-tin-oxide (ITO) nanowhiskers (NWhs) as transparent electrodes. More than 360 degrees of phase shift at 1.0 THz was achieved at a driving voltage as low as similar to 2.6 V (rms). This is approximately 40 times smaller than that reported in previous works using an electrically tuned LC device. Significance of the NWhs in reducing the required voltage is demonstrated. Overall transmittance of the device is as high as 30%, which is accountable by absorption losses of ITO NWhs, quartz substrate and LC. Experimental results are in good agreement with a theoretical formulism while taking into account super-thick LC cells (similar to 1 mm) and pretilt angles. We also propose and demonstrate a novel THz technique for measuring pretilt angles of liquid crystals.
Multi-band filter design with less total film thickness for short-wave infrared
(2017-01-01)
Yan, Yung-Jhe
;
Chien, I-Pen
;
Chen, Po-Han
;
Chen, Sheng-Hui
;
Tsai, Yi-Chun
A multi-band pass filter array was proposed and designed for short wave infrared applications. The central wavelength of the multi-band pass filters are located about 905 nm, 950 nm, 1055 nm and 1550 nm. In the simulation of an optical interference band pass filter, high spectrum performance (high transmittance ratio between the pass band and stop band) relies on (1) the index gap between the selected high/low-index film materials, with a larger gap correlated to higher performance, and (2) sufficient repeated periods of high/low-index thin-film layers. When determining high and low refractive index materials, spectrum performance was improved by increasing repeated periods. Consequently, the total film thickness increases rapidly. In some cases, a thick total film thickness is difficult to process in practice, especially when incorporating photolithography liftoff. Actually the maximal thickness of the photoresist being able to liftoff will bound the total film thickness of the band pass filter. For the application of the short wave infrared with the wavelength range from 900nm to 1700nm, silicone was chosen as a high refractive index material. Different from other dielectric materials used in the visible range, silicone has a higher absorptance in the visible range opposite to higher transmission in the short wave infrared. In other words, designing band pass filters based on silicone as a high refractive index material film could not obtain a better spectrum performance than conventional high index materials like TiO2 or Ta2O5, but also its material cost would reduce about half compared to the total film thickness with the conventional material TiO2. Through the simulation and several experimental trials, the total film thickness below 4 um was practicable and reasonable. The fabrication of the filters was employed a dual electric gun deposition system with ion assisted deposition after the lithography process. Repeating four times of lithography and deposition process and black matrix coating, the optical device processes were completed.
Projected Efficiency of Organic/Inorganic Hybrid Tandem Solar Cells
(2013)
Chen, Po-Han
;
Huang, Yang-Yue
;
Pen, Huai-Te
;
Lai, Yi-Chun
;
Tsai, Chia-Ying
We propose a series-connected hybrid tandem solar cell which consists of an organic solar cell (P3HT/PCBM) as the top cell and an organic/crystalline silicon hybrid solar cell (PEDOT:PSS/c-Si nanowires) as the bottom cell. Based on the device structure, the organic materials can be directly spun-cast onto the inorganic silicon substrate with thermally evaporated metal contacts, making solution-based processes possible for rapid and low-cost production. With a proper design, the hybrid device architecture can achieve a high open-circuit voltage and junction-matched photocurrent, offering a promising approach for next-generation high-efficiency photovoltaics. In this work, we established a device model to investigate the photovoltaic characteristics of the proposed hybrid tandem solar cells by combining the organic and hybrid silicon solar cells with a hypothetic recombination layer (RL). First, the model of single junction solar cells is fitted to the current-voltage curve of fabricated devices. Next, we investigate the properties of the RL between the sub-cells and observe strong correlations with the photovoltaic performance of tandem cells. In our preliminary model, we have realized a cell with an open-circuit voltage (Voc), short-circuit current (Jsc), fill-factor (FF) and power conversion efficiency (PCE) of 1.093 V, 9.715 mAkm2, 43.725 % and 4.644 %, respectively. We will further tailor the properties of the RL, the active-layer thickness of sub-cells, as well as the band alignment, in order to achieve practical device designs. Currently, the characteristics of real hybrid tandem solar cells remain significantly lower than the simulation result. The reason of such limited cell performance is the poor interfacial contact, which makes it difficult to provide efficient recombination and transport for electrons and holes generated from sub-cells. A number of challenging issues, including interface physics and device design will be discussed.
Ubiquitous carrier harvesting in organic solar cells with embedded indium-tin-oxide nano-electrodes
(2013-11-01)
Hsu, Min-Hsiang
;
Chen, Po-Han
;
Yu, Peichen
;
Huang, Jen-Hsien
;
Chang, Chia-Hua
Bulk heterojunction in organic solar cells allows adequate interfaces for the dissociation of photo-generated excitons. However, the intermixed donor- and acceptor-like materials do not guarantee successful carrier transport and collections. In this work, we demonstrate ubiquitous carrier harvesting characteristics by using embedded indium-tin-oxide nano-electrodes (NEs) with a conformal electro-polymerized coating of a hole conducting layer. Compared to its planar electrode counterpart, this device exhibits internal quantum efficiency insensitive to the distribution of carrier generation, as determined by angle-resolved absorption spectroscopy and photocurrent characteristics. The ubiquitous carrier harvesting characteristics offer a viable solution to organic thin-film devices fabricated on flexible substrates or operated under diffused ambient light. (C) 2013 Elsevier B.V. All rights reserved.
Voltage-controlled liquid-crystal terahertz phase shifter with indium-tin-oxide nanowhiskers as transparent electrodes
(2014-04-15)
Yang, Chan-Shan
;
Tang, Tsung-Ta
;
Chen, Po-Han
;
Pan, Ru-Pin
;
Yu, Peichen
Indium-tin-oxide nanowhiskers were employed as transparent electrodes in a liquid-crystal terahertz phase shifter. Transmittance of the device was as high as similar to 75%. Phase shift exceeding pi/2 at 1.0 THz is achieved in a similar to 500 mu m-thick cell. The driving voltage required for the device operating as a quarter-wave plate was as low as 17.68 V (rms), an improvement of nearly an order of magnitude over previous work. (C) 2014 Optical Society of America