Browsing by Author "Pan, Huai-Te"

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10% Efficiency Hybrid GaAs/PEDOT:PSS Solar Cells with Monolayer Graphene
(2014-01-01)
Cheng, Kai-Yuan
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Pan, Huai-Te
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Yu, Shu-Cheng
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Weng, Wei-Sheng
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Lai, Yi-Chun
The development of solution-processed hybrid organic-inorganic heterojunction solar cells have provoked increasing research effort due to potential to significantly reduce the fabrication cost of semiconductor solar cells while maintaining the high power conversion efficiency (PCE). With a recent record of GaAs solar cells achieving 28.8% via a wafer lift-off technique, hybrid organic/GaAs solar cells can offer an alternative route to provide more affordable solar power than current semiconductor technologies. In this work, we demonstrate the hybrid devices based on a conductive polymer poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) directly spun-cast on planar gallium arsenide materials. While still lacking for optimized antireflection, the PCE of the best performing device can achieve nearly 10% by introducing the monolayer graphene as transparent electrode. The current progress presents 2-fold enhancement in comparison to a previous record at 5% based on GaAs nanowire templates.
13% Efficiency Hybrid Organic/Silicon-Nanowire Heterojunction Solar Cell via Interface Engineering
(2013-12-01)
Yu, Peichen
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Tsai, Chia-Ying
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Chang, Jan-Kai
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Lai, Chih-Chung
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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.
Conductive Polymer/GaAs Hybrid Heterojunction Photovoltaic Devices
(2013)
Pan, Huai-Te
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Huang, Yang-Yue
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Weng, Wei-Sheng
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Chen, Po-Han
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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.
FABRICATION AND MODELING OF LARGE-SCALE SILICON NANOWIRE SOLAR CELLS FOR THIN-FILM PHOTOVOLTAICS
(2012)
Cheng, Yu-Chih
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Chen, Ting-Gang
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Chang, Feng-Yu
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Huang, Bo-Yu
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Pan, Huai-Te
Nanostructured crystalline silicon is promising for thin photovoltaic devices due to reduced material usage and wafer quality constraint. In this study, a simple and cost-effective method is presented for producing large-area silicon nanowire (SiNW) arrays with various lengths by employing the polystyrene nanosphere lithography and the metal-assisted chemical etching (MACE). The nanowire structure exhibits broadband and omnidirectional antireflection properties, where the lowest AM1.5G-spectrum-weighted reflectance of SiNW arrays is 4.38%, compared to 8.84% of the conventional single layer antireflection coating (SLARC). Next, we made SiNW array structures into solar cells and its power efficiency achieved 10.8%. Afterward, the SiNW array solar cells were analyzed by external and internal quantum efficiency measurement which shows the device performance primarily limited by direct and indirect interfacial recombination of charge carriers. We further develop a modeling technique based on three-dimensional (3) optical and two-dimensional (20) electrical simulations which are tailored for the nanostructured silicon photovoltaic devices. The optical simulation employs a rigorous couple wave analysis (RCWA) technique to calculate the distribution of electromagnetic field in order to obtain the generation rate within the nanostructure. Next, an electrical calculation is based on a 20 self-consistent drift-diffusion and Poisson solver using a finite element method (FEM). We investigate the influence to the device performance of carrier diffusion length with three different structures. The simulation results show that a short diffusion length does not seriously deteriorate the short-circuit current density and power conversion efficiency of a core-shell PN junction solar cell compared to the conventional planar structure. Our work suggests that SiNW solar cells can achieve efficient light harvesting and photoelectric conversion with less and lower-grade materials than the conventional technology, which is promising for thin silicon photovoltaics.
Flexible Silver Nanowire Meshes for High-Efficiency Microtextured Organic-Silicon Hybrid Photovoltaics
(2012-12-01)
Chen, Ting-Gang
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Huang, Bo-Yu
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Liu, Hsiao-Wei
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Huang, Yang-Yue
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Pan, Huai-Te
Hybrid organic-silicon heterojunction solar cells promise a significant reduction on fabrication costs by avoiding energy-intensive processes. However, their scalability remains challenging without a low-cost transparent electrode. In this work, we present solution-processed silver-nanowire meshes that uniformly cover the microtextured surface of hybrid heterojunction solar cells to enable efficient carrier collection for large device area. We systematically compare the characteristics and device performance with long and short nanowires with an average length/diameter of 30 mu m/115 nm and 15 mu m/45 nm, respectively, to those with silver metal grids. A remarkable power conversion efficiency of 10.1% is achieved with a device area of 1 x 1 cm(2) under 100 mW/cm(2) of AM1.5G illumination for the hybrid solar cells employing long wires, which represents an enhancement factor of up to 36.5% compared to the metal grid counterpart. The high-quality nanowire network displays an excellent spatial uniformity of photocurrent generation via distributed nanowire meshes and low dependence on efficient charge transport under a high light-injection condition with increased device area. The capability of silver nanowires as flexible transparent electrodes presents a great opportunity to accelerate the mass deployment of high-efficiency hybrid silicon photovoltaics via simple and rapid soluble processes.