Solar cells with increased short‐circuit current density and energy conversion efficiency can be realized by integrating moth eye textures in the design of perovskite and amorphous silicon thin film solar cells. Broadband light incoupling in solar cells can be achieved by using hexagonally arranged arrays of nipples or domes with parabolically shaped surface profiles. The moth eye surface texture represents a refractive index grating that allows for an efficient incoupling of light in the solar cell while minimizing reflection losses. The light incoupling is studied for perovskite and amorphous silicon solar cells. Perovskite has a rather low refractive index of ≈2.5, while amorphous silicon exhibits a refractive index of ≈4.5 comparable to that of crystalline silicon. Due to largely different refractive indices, different device designs must be selected to allow for an efficient light incoupling in the solar cell. 3D finite‐difference time‐domain simulations are used for the optical modeling. Design guidelines are provided on how to realize perovskite and silicon thin film solar cells with high quantum efficiency and short‐circuit current by using moth eye textures.

Light trapping and photon management of silicon thin film solar cells can be improved by a separate optimization of the front and back contact textures. A separate optimization of the front and back contact textures is investigated by optical simulations taking realistic device geometries into consideration. The optical simulations are confirmed by experimentally realized 1 μm thick microcrystalline silicon solar cells. The different front and back contact textures lead to an enhancement of the short circuit current by 1.2 mA/cm2 resulting in a total short circuit current of 23.65 mA/cm2 and an energy conversion efficiency of 8.35%.

A simple method is developed to determine the light trapping properties of arbitrarily textured solar cells with high accuracy. The method allows for determining the quantum efficiency and short circuit current density of thin film solar cells prepared on randomly nanotextured surfaces. The light trapping of the randomly textured solar cell is described by the area weighted superposition of periodically textured solar cells. The necessary input parameters for the calculations are determined by analyzing the randomly textured surfaces of the solar cells using atomic force microscopy and image processing. The analysis of the atomic force microscope images and the calculation of the quantum efficiency and short circuit current can be determined from current maps, without complex and time-consuming calculations. The calculated solar cell parameters exhibit excellent agreement with experimentally measured quantum efficiencies and short circuit current densities for amorphous and microcrystalline silicon thin film solar cells prepared on randomly textured substrates. Finally, the work contributes to a comparison of random and periodic light trapping structures.

A simple and fast method was developed to determine the quantum efficiency and short circuit current of thin-film silicon solar cells prepared on periodically or randomly textured surfaces. The optics was studied for microcrystalline thin-film silicon solar cells with integrated periodic and random surface textures. Rigorous Coupled Wave Analysis (RCWA) was used to investigate the behaviour of the solar cells. The analysis of the periodic and random textured substrates allows for deriving optimal surface textures. Furthermore, light trapping in periodic and randomly textured substrates will be compared.

Light trapping and plasmonic effects in silicon thin-film solar cells were investigated experimentally and numerically. The performances of microcrystalline and amorphous silicon solar cells strongly depend on the morphology of the metal back contact.

Nanotextured contact layers are used in silicon thin film solar cells for increasing the short circuit current and conversion efficiency. We developed an approach to analyze random nanotextured surfaces by atomic force microscopy and image segmentation. It was used to investigate sputtered and wet chemically etched aluminum doped zinc oxide films with various morphologies. The information extracted from the surfaces was correlated with optical simulations of periodically textured thin film solar cells. The results from the surface analysis and optical simulations were also compared with the experimental results obtained for amorphous silicon solar cells prepared on the nanotextured substrates.

The optical enhancement and losses of microcrystalline thin-film silicon solar cells with periodic pyramid textures were investigated. Using a finite difference time domain algorithm, the optical wave propagation in the solar cell structure was calculated by rigorously solving the Maxwell’s equations. The influence of the profile dimensions (the period and height of the pyramid) and solar cell thickness on the quantum efficiency and short circuit current were analyzed. Furthermore, the influence of the solar cell thickness on the upper limit of the short circuit current was investigated. The numerically simulated short circuit currents were compared to fundamental light trapping limits based on geometric optics. Finally, optical losses in the solar cell were analyzed. After identifying these key losses, strategies for minimizing the losses can be discussed.

Plasmonic effects in microcrystalline silicon thin-film solar cells with textured front contacts and back reflectors were investigated. Nanotexturing of the front contact of the thin film-solar cell leads to enhanced light trapping, while the nanotextured back reflector allows for the formation of localized plasmonic resonances, which partially contribute to light scattering and partially to optical losses. The interplay between light trapping and plasmonic losses was investigated and strategy will be presented to tune surface plasmon resonances and increase the short circuit current and quantum efficiency.

The optics of microcrystalline thin-film silicon solar cells with textured interfaces was investigated. The surface textures lead to scattering and diffraction of the incident light, which increases the effective thickness of the solar cell and results in a higher short circuit current. The aim of this study was to investigate the influence of the frontside and the backside texture on the short circuit current of microcrystalline thin-film silicon solar cells. The interaction of the front and back textures plays a major role in optimizing the overall short circuit current of the solar cell. In this study the front and back textures were approximated by line gratings to simplify the analysis of the wave propagation in the textured solar cell. The influence of the grating period and height on the quantum efficiency and the short circuit current was investigated and optimal grating dimensions were derived. The height of the front and back grating can be used to control the propagation of different diffraction orders in the solar cell. The short circuit current for shorter wavelengths (300-500 nm) is almost independent of the grating dimensions. For intermediate wavelengths (500 nm - 700 nm) the short circuit current is mainly determined by the front grating. For longer wavelength (700 nm to 1100 nm) the short circuit current is a function of the interaction of the front and back grating. An independent adjustment of the grating height of the front and the back grating allows for an increased short circuit current.

The optics of thin-film microcrystalline silicon solar cells with integrated 3-D pyramid-like surface texture was investigated. The influence of the dimensions of the surface texture on the quantum efficiency and short circuit current was evaluated.

Nipples on the surface of moth eye facets exhibit almost perfect broadband anti-reflection properties. We have studied the facet surface micro-protuberances, known as corneal nipples, of the chestnut leafminer moth Cameraria ohridella by atomic force microscopy, and simulated the optics of the nipple arrays by three-dimensional electromagnetic simulation. The influence of the dimensions and shapes of the nipples on the optics was studied. In particular, the shape of the nipples has a major influence on the anti-reflection properties. Furthermore, we transferred the structure of the almost perfect broadband anti-reflection coatings to amorphous silicon thin film solar cells. The coating that imitates the moth-eye array allows for an increase of the short circuit current and conversion efficiency of more than 40%.

A simple and fast method was developed to determine the optimal surface texture of thin-film silicon solar cells. The optical wave propagation was studied for microcrystalline thin-film silicon solar cells with integrated line and triangular gratings. The developed method based on rigorous coupled wave analysis provides a good agreement with experimental data. The short circuit current is enhanced by 60% up to 20-21 mA/cm(2) for grating periods of 500-700 nm and grating heights of 300-500 nm. The method facilitates an analysis of nanotextured solar cells which is 20 times faster than conventional approaches like finite difference and finite integral simulations. (c) 2010 The Japan Society of Applied Physics

The optics of microcrystalline silicon thin-film solar cells with integrated light trapping structures was investigated. Periodic grating couplers were integrated in microcrystalline silicon thin-film solar cells and the influence of the grating dimensions on the short circuit current and the quantum efficiency was investigated by the numerical simulation of Maxwell’s equations utilizing the finite difference time domain algorithm. The grating structure leads to scattering and higher order diffraction resulting in an increased absorption of the incident light in the silicon thin-film solar cell. The influence of the grating period and the grating height on the short circuit current and the quantum efficiency was investigated. Enhanced quantum efficiencies are observed for the red and infrared parts of the optical spectrum. Optimal dimensions of the grating coupler were obtained.

The influence of nano textured front contacts on the optical wave propagation within microcrystalline thin-film silicon solar cell was investigated. Periodic triangular gratings were integrated in solar cells and the influence of the profile dimensions on the quantum efficiency and the short circuit current was studied. A Finite Difference Time Domain approach was used to rigorously solve the Maxwell's equations in two dimensions. By studying the influence of the period and height of the triangular profile, the design of the structures were optimized to achieve higher short circuit currents and quantum efficiencies. Enhancement of the short circuit current in the blue part of the spectrum is achieved for small triangular periods (P<200 nm), whereas the short circuit current in the red and infrared part of the spectrum is increased for triangular periods (P = 900nm) comparable to the optical wavelength. The influence of the surface texture on the solar cell performance will be discussed.

Light trapping in microcrystalline silicon thin-film solar cells with integrated lamellar gratings was investigated. The influence of the grating dimensions on the short circuit current and quantum efficiency was investigated by numerical simulation of Maxwell's equations by a Finite Difference Time Domain approach. For the red and infrared part of the optical spectrum, the grating structure leads to scattering and higher order diffraction resulting in an increased absorption of the incident light in the silicon thin-film solar cell. By studying the diffracted waves arising from lamellar gratings, simple design rules for optimal grating dimensions were derived.