Hong-Jhang Syu

Low-Pressure-Assisted Coating Method To Improve Interface between PEDOT:PSS and Silicon Nanotips for High-Efficiency Organic/Inorganic Hybrid Solar Cells via Solution Process

UNLABELLED Nanostructured silicon hybrid solar cells are promising candidates for a new generation photovoltaics because of their light-trapping abilities and solution processes. However, the performance of hybrid organic/Si nanostructure solar cells is hindered because of carrier recombination at surface and poor coverage of organic material poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) on nanostructures. Here we demonstrate low-pressure-assisted coating method of PEDOT PSS on surface-modified silicon nanotips with broadband light-trapping characteristics to improve interface property and to achieve high-efficiency hybrid solar cells through a solution process. The approach enhances the effective minority-carrier lifetime and the coverage of PEDOT PSS on the surface of nanostructures. Hybrid solar cells fabricated with surface-modified nanotips exhibit a high fill factor of 70.94%, short-circuit current density of 35.36 mA/cm(2), open-circuit voltage of 0.528 V, and power conversion efficiency of 13.36%. The high efficiency and the high fill factor are achieved because of conformal coating of PEDOT PSS via a low-pressure-assisted coating process, excellent light harvesting without sacrificing the minority-carrier lifetime, and efficient charge separation/collection of photogenerated carriers.

Optical trapping enhancement from high density silicon nanohole and nanowire arrays for efficient hybrid organic–inorganic solar cells

In this paper, we employ a series of metal-assisted chemical etching processes to fabricate low-cost silicon nanohole (SiNH) and silicon nanowire (SiNW) arrays for hybrid solar cells. The SiNH arrays and SiNW arrays are obtained by a two-step etching and one-step etching technique, respectively. Length and depth of SiNWs and SiNHs can be controlled by etching time. The SiNH arrays demonstrate higher optical trapping effect than SiNW arrays, resulting in leading performance power conversion efficiency of 11.25% in the hybrid organic–inorganic solar cells. SiNH arrays have a high surface area, compared to SiNW arrays, so they can give rise to more junction area in the organic–inorganic heterojunction structures. In addition, these SiNH arrays possess additional advantages of robust structures and higher density with low air-filling fraction as compared to SiNW arrays. Furthermore, the SiNH arrays show superior efficiency to SiNW arrays experimentally. In particular, the fabricated SiNH arrays with high density can suppress the optical reflection well below 5% over a broad wavelength range from 300 to 1100 nm in a short nanohole depth. The very low reflectance and excellent light trapping property are attributed to the sub-wavelength dimension of the SiNH structure. These SiNH arrays not only facilitate the optical trapping, but also provide efficient broadband and omnidirectional photon harvests for cost-effective future nanostructured photovoltaics.

Performance-Enhanced Textured Silicon Solar Cells Based on Plasmonic Light Scattering Using Silver and Indium Nanoparticles

Performances of textured crystalline-silicon (c-Si) solar cells enhanced by silver nanoparticles (Ag-NPs) and indium nanoparticles (In-NPs) plasmonic effects are experimentally demonstrated and compared. Plasmonic nanoparticles integrated into textured c-Si solar cells can further increase the absorption and enhance the short-circuit current density (Jsc) of the solar cell. To examine the profile of the proposed metallic particles, the average diameter and coverage of the In-NPs (Ag-NPs) at 17.7 nm (19.07 nm) and 30.5% (35.1%), respectively, were obtained using scanning electron microscopy. Optical reflectance and external quantum efficiency response were used to measure plasmonic light scattering at various wavelengths. Compared to a bare reference cell, the application of In-NPs increased the Jsc of the cells by 8.64% (from 30.32 to 32.94 mA/cm2), whereas the application of Ag-NPs led to an increase of 4.71% (from 30.32 to 31.75 mA/cm2). The conversion efficiency of cells with embedded In-NPs (14.85%) exceeded that of cells with embedded Ag-NPs (14.32%), which can be attributed to the broadband plasmonic light scattering of the In-NPs.

Interface modification for efficiency enhancement in silicon nanohole hybrid solar cells

In this paper, the interface between Si nanoholes (SiNHs) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated and improved to achieve high-efficiency SiNH/PEDOT:PSS hybrid solar cells. The high-density SiNHs are fabricated using short-time Ag deposition before metal-assisted chemical etching (MacEtch) method. Also, a polymer coverage method is explored to overcome the difficulty of PEDOT:PSS infiltration into SiNHs. PEDOT:PSS is mixed with co-solvent dimethylsulfoxide (DMSO) to have better polymer infiltrate into SiNHs via two-step coating process. This technique significantly improves the interface between SiNHs and PEDOT:PSS; the greatly reduced contact angle from 90° to 16° at the interface of Si and PEDOT:PSS has established this fact. In addition, the minority carrier lifetime is dramatically increased from 31.52 to 317.20 μs. The property improvement enables the SiNH/PEDOT:PSS hybrid solar cell with high Jsc of 36.80 mA cm−2, Voc of 0.524 V, FF of 66.50%, and thus PCE of 12.82%. Also, the SiNH structures have an excellent light-trapping effect, which contributes to very low average total reflectance of 3%, due to internal multiple reflections caused by subwavelength features. At an angle of incidence up to 60°, the specular reflectance maintains at as low as 1%; even at a large angle of 70°, the reflectance is still below 10%. This work provides a feasible solution process to fabricate SiNH structure and to improve organic/Si hybrid solar cells in energy and cost-effective manner.

Analysis of the PEDOT:PSS/Si nanowire hybrid solar cell with a tail state model

In this paper, the electrical properties of the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/silicon nanowire hybrid solar cell have been analyzed and an optimized structure is proposed. In addition, the planar PEDOT:PSS/c-Si hybrid solar cell is also modeled for comparison. We first developed a simulation software which is capable of modeling organic/inorganic hybrid solar cells by including Gaussian shape density of states into Poisson and drift-diffusion solver to present the tail states and trap states in the organic material. Therefore, the model can handle carrier transport, generation, and recombination in both organic and inorganic materials. Our results show that at the applied voltage near open-circuit voltage (Voc), the recombination rate becomes much higher at the PEDOT:PSS/Si interface region, which limits the fill factor and Voc. Hence, a modified structure with a p-type amorphous silicon (a-Si) layer attached on the interface of Si layer and an n+-type Si layer inser...

Fabrication of silicon nanowire/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-graphene oxide hybrid solar cells

Silicon nanowire (SiNW)/Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) Schottky junctions have shown great promise as high efficiency, cost effective solar cells. Here, hybrid SiNWs/PEDOT:PSS blended graphene oxide (GO) solar cells are prepared and investigated. The SiNWs/PEDOT:PSS blended GO cells show enhanced light trapping and a large junction area when compared to pure PEDOT:PSS structures. SiNWs combined with GO solar cells show energy conversion efficiencies of up to 9.57% under the AM 1.5G condition, opening the possibility of using semiconductor/graphene oxide in photovoltaic applications.

Fabrication of Silicon Nanostructured Thin Film and Its Transfer from Bulk Wafers onto Alien Substrates

Various Si nanostructures can be fabricated using a metal-assisted etching technique, which must be applied on bulk Si wafers, limiting its applications and wasting a significant amount of material. Here, we report a technique to form a Si nanostructured thin film created by metal-assisted chemical etching from bulk Si wafers and to transfer it onto alien substrates. To detach the Si nanostructured thin films completely from bulk Si wafers, a second-step metal-assisted chemical etching made the root of the Si nanostructures become fragile. The transferred Si nanostructures are well-aligned along the normal direction of the receiver substrate. The X-ray diffraction spectrum reveals that the transferred Si nanostructured thin films exhibit good crystal orientation and morphology. A strong light trapping effect between the nanostructures causes such films of 16 μm thickness to exhibit nearly 99% absorption from 400 to 800 nm. This exceeds the theoretically calculated limits of planar Si.

Effect of nanowire length to silicon nanowire/PEDOT:PSS solar cells

Silicon nanowire (SiNW)/Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells were fabricated by solution process. The effect of nanowire length to cell performance was investigated for the nanowire length varying from 0.73 μm to 5.59 μm. The nanowire length was found to have negative effect on the power conversion efficiency (PCE), in the condition of the fixed thickness of PEDOTPSS. The highest PCE of 7.02% was obtained for the wire length of 0.73 μm.

Fabrication of Multiple Si Nanohole Thin Films from Bulk Wafer by Controlling Metal-Assisted Etching Direction

Crystalline Si photovoltaic modules still have high production cost due to significant consumption of the Si wafer. Reducing the large amount of Si material consumption is thus a critical issue. Here we develop a two-step metal-assisted etching technique for forming vertically-aligned Si nanohole thin films from bulk Si wafers. The formation of Si nanohole thin films includes a series of solution processes: deposition of Ag nanoparticles in an AgNO3/ HF aqueous solution, formation of Si nanohole arrays at the first-step metal-assisted etching, and side etching of the roots of the nanohole structure at the second-step metal-assisted etching. All the processes can proceed at around room temperature. A Si nanohole thin film with an average hole-size of 100 nm and a thickness of 5ìm-20ìm was hence formed at the top of the wafer. Afterwards, the Si nanohole thin film was transferred onto alien substrates. The Si nanohole thin film has the crystal quality similar to the bulk Si wafer. The above bulk Si substrate can be reused. With similar processes, other Si nanohole thin films can be formed from the above recycled Si wafer. The hole size and thickness are similar. The Si wafers recycled will significantly reduce the material consumption of Si. Thus, such technique is promising for lowering the cost of Si solar cells.m.

Layer transfer of crystalline Si thin film by metal-assisted chemical etching concerning different H 2 O 2 /HF ratios

Thin-film crystalline photovoltaic (PV) cell is a trend for future PV with its potential to achieve low cost and high efficiency. Concerning material utilization efficiency, we propose a method with a fast manufacturing method of thin crystalline Si by chemical solution. To obtain the highest efficiency of material utilization, experiments with different H2O2/HF ratio are conducted, where related mechanisms are discussed. Moreover, large-area (87.7 mm2) thin film transferred to glass is demonstrated, and with embedded nanohole structure, lowest optical reflectance of 0.26% is measured. These characteristics show that the fabricated thin film has potential for large-area crystalline thin film PV.