Chen-Chih Hsueh

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.

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.

Flexible silicon thin film organic/inorganic hybrid solar cells

Compare with different thickness silicon thin film, 30μm, 50μm and 100μm, we demonstrate a promising way to form 30μm silicon thin film hybrid solar cells with good bending property, by using the silicon nanostructure (SiNS) to achieve low reflection and increase heterojunction areas, the device performance is enhanced to 10.15%.

Modified Silicon nanotips with improved carrier lifetime by using solution process for efficient solar cells applications

In this work, a simple solution process (metal-assisted wet chemical etching [MacEtch] method) is used to fabricate high-density silicon nanohole (SiNH) arrays on n-type wafer. SiNH arrays generally produce a large surface-area-to-volume ratio, so that aid for strong light trapping effect between the nanostructures causes high absorption and charge collection via the formation of a core-sheath p-n junction. However, the photogenerated excited carriers are easily trapped by high-density surface defects due to higher surface area prolonging to depth of nanohole (NH). To reduce the surface defects and metal contamination of SiNHs formed by metal-catalyst etching, it is important to further proceed to feasible simple solution treatment. Applying the chemical polishing etching (CPE) treatment to SiNH surface leads to smooth and contamination-free surface. In addition, all the processes mentioned here are energy and cost-efficient.

Novel fabrication of Si thin film for solar cell applications

We demonstrate a novel method to fabricate crystalline silicon thin film for solar cell applications. It can reduce material cost and energy consumption. Here, we adopt a multi-step metal-assisted chemical etching procedure by using silver as catalyst to form silicon thin film. Through engineering the etching direction, this method provides possibility to fabricate transferable silicon thin film. Moreover, the substrate can be reused for further thin film fabrication.

High efficiency hybrid organic/silicon-nanohole heterojunction solar cells

In this work, a simple method of solution process to fabricate high density Silicon nanohole (SiNH) arrays on n-type wafer is experimented. SiNHs exhibit very low reflectance from range of wavelength 300 to 1100 nm irrespective of the angle of incidence, better than Si nanowires. The SiNH arrays have a strong light trapping effect between the nanostructures causes high absorption. We experimentally demonstrate high-efficiency organic-inorganic hybrid solar cells, Si/PEDOT:PSS with silicon nanoholes. Such Si/PEDOT:PSS hybrid solar cells exhibit high Jsc of 36.80 mA/cm2, Voc of 0.52V, FF of 66.50%, and thus power conversion efficiency (PCE) of 12.72%. SiNH arrays produce 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.

Fabrication of Silicon thin film by metal-assisted chemical etching

We fabricate a Silicon thin film by metal-assisted chemical etching (MacEch). Generally, it is hard to make a large size silicon thin film. Here we demonstrate a low cost and simple method to lift off the silicon thin film from silicon wafer. Besides, the substrate is reusable, so we can fabricate many thin films from the same wafer. Thus, this method is competitive for commercial applications.

Morphology dependence of silicon nanostructure/organic polymer solar cell

Si nanohole and nanowire/organic polymer solar cell is fabricated by low temperature and simple spin-coating method. The results show that the nanohole device performance is better than that of nanowire device. The Si nanohole device has higher external quantum efficiency in all wavelengths. The reason for the enhancement is analyzed from optical reflectance and the observation between Si nanohole and PEDOT:PSS interface. With nanohole structure, the short-circuit current density is increased from 22.1 to 26.9 mA/cm2 (22% increase), and the power conversion efficiency is enhanced from 7.4% to 8.0%. Nanohole structure is promising for high-efficiency Si/organic polymer solar cell.

Fabrication of large-scaled synergetic silicon nanowire arrays using metal-assisted chemical etching for solar cell applications

We fabricate Silicon nanowire (SiNW) arrays for solar-cell applications on 6-inch wafers employing metal-assisted chemical etching (MacEtch). It can reduce cost and energy consumption. However it is difficult to make uniform SiNW arrays on large size wafer. Here we demonstrate a simple method to achieve a uniform SiNW on 6 inch wafers. Moreover, optical properties and surface morphologies of 6 inch N-type pyramid/SiNW arrays and 6 inch P-type as-cut/SiNW arrays are investigated. Reflectance indicates the extensive light-trapping effect by the SiNW arrays. Thus, the improved MacEtch method is promising for future commercial mass production on large size wafers.