Wendi Zhang

Fabrication of Light-Scattering Multiscale Textures by Nanoimprinting for the Application to Thin-Film Silicon Solar Cells

In this study, nanoimprint processing was used to realize various multiscale textures on glass substrates for application in thin-film photovoltaic devices. The multiscale textures are formed by a combination of large and small features, which proofed to be beneficial for light trapping in silicon thin-film solar cells. Two approaches for the fabrication of multiscale textures are presented in this study. In the first approach, the multiscale texture is realized at the lacquer/transparent conductive oxide (TCO) interface, and in the second approach, the multiscale texture is realized at the TCO/Si interface. Various types of multiscale textures were fabricated and tested in microcrystalline thin-film silicon solar cells in p-i-n configuration to identify the optimal texture for the light management. It was found that the best light-scattering multiscale texture was realized using an imprint-textured glass substrate, which contains large craters, in combination with HF-etched TCO (ZnO:Al), which contains small features, on top of the imprint. With this structure (of the second approach), the short-circuit current density of the solar cell devices was improved by 0.6 mA/cm-2 using multiscale textures realized by nanoimprint processing.

Influence of Interface Textures on Light Management in Thin-Film Silicon Solar Cells With Intermediate Reflector

High-efficiency thin-film silicon solar cells require advanced textures at the front contacts for light management. In this contribution, the influence of the texture of various transparent conductive oxides (TCO) on the effectiveness of an intermediate reflector layer (IRL) in a-Si:H/μc-Si:H tandem solar cells is investigated. The employed front side TCOs include several types of sputter-etched ZnO:Al, LPCVD ZnO:B and APCVD SnO2:F. The topographies after different stages of the deposition process of the tandem solar cell, at the front TCO, after deposition of the amorphous top cell and after the deposition of the microcrystalline bottom cell, were characterized by atomic force microscopy at precisely the same spot. The external quantum efficiency of the fabricated solar cells were measured and successfully reproduced by a finite-difference time-domain method applying the measured topographies at each interface of the solar cell. With these simulations, the impact of structure type and feature size on the effectiveness of the IRL is investigated. The highest IRL effectiveness in a tandem solar cell was found for double-textured ZnO:Al. In this contribution, we study the interplay between interface textures and parasitic losses. Our findings are relevant for the design of topography for optimized IRL performance.

Preparation and topography analysis of randomly textured glass substrates

Randomly textured glass sheets in combination with a transparent conductive layer are promising as front contacts for silicon based thin-film solar cells. The authors have developed a novel method to create randomly textured glass surfaces. For the fabrication a wet chemically textured zinc oxide (ZnO) film is used as three dimensional etch mask and its surface topography is transferred to the glass substrate by ion beam etching. The typical texture of the sputtered and etched ZnO film exhibits craterlike features, which can be tuned by a variation of the initial ZnO film thickness and the etching time. Thus, the surface features of the resulting rough glass can be varied within a wide range. Its topography exhibits a maximum root mean square roughness of more than 200 nm with a lateral correlation length around 1500 nm. Microcrystalline silicon solar cells on the textured glass substrates show an increase of the short circuit current density by 36% compared to cells on flat glass. This proves the improve...