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A silicon heterojunction solar cell using silicon carbide as front contact is presented, which features the main advantage of high transparency. To enhance this advantage, an optical loss analysis is performed. It is found that reflection losses play an important role for the solar cell, which can easily be reduced by applying an additional MgF2 coating. The deposition of the coating degrades the passivation quality of the contact but can be cured, eventually leading to a certified short circuit current density of 40.9 mA/cm² and efficiency of 23.99%. Afterwards, a roadmap to a theoretical efficiency of 25% is presented.

To optimize the electrical performance of silicon heterojunction solar cell devices, the electronic properties and microstructure of n-type nc-Si:H were characterized and analyzed. It was found that higher conductivity and crystalline volume fraction (F c ) of nc-Si:H can be obtained at lower silane gas fraction (f SiH4 ), lower power and higher phosphorous gas fraction (f PH3 ). In our case, there is a decline of the passivation for the devices with nc-Si:H after sputtering process. By increasing the phosphine flow fraction, the sputter damage can be reduced and 3% abs gain of FF as well as 0.7% abs gain of efficiency is reached compared with reference. The best solar cell exhibits the V oc of 733.3 mV, FF of 79.7%, J sc of 39.00 mA/cm2 and η of 22.79% at the M2 size wafer.

Silicon heterojunction with nc-SiC(n)/SiO 2 based front transparent passivating contact (TPC) is numerically modeled. The model is then used to study the effect of active dopant concentration at the front and rear contact of the solar cell. A potential of power conversion efficiency above 25 % can be achieved with a suitable acceptor dopant concentration of p-type amorphous silicon at the rear side. Improving fill factor via SiC dopant concentration can enhance the cell power conversion efficiency within a narrow range of active dopant concentration. However, very high doping of SiC can affect the cell performance negatively.

This work presents a review of life-cycle assessment (LCA) studies of hydrogen electrolysis using power from photovoltaic (PV) systems. The paper discusses the assumptions, strengths and weaknesses of 13 LCA studies and identifies the causes of the environmental impact. Differences in assumptions of system boundaries, system sizes, evaluation methods, and functional units make it challenging to directly compare the Global Warming Potential (GWP) resulting from different studies. To simplify this process, 13 selected LCA studies on PV-powered hydrogen production have been harmonized following a consistent framework described by this paper. The harmonized GWP values vary from 0.7 to 6.6 kg CO2-eq/kg H2 which can be considered a wide range. The maximum absolute difference between the original and harmonized GWP results of a study is 1.5 kg CO2-eq/kg H2. Yet even the highest GWP of this study is over four times lower than the GWP of grid-powered electrolysis in Germany. Due to the lack of transparency of most LCAs included in this review, full identification of the sources of discrepancies (methods applied, assumed production conditions) is not possible. Overall it can be concluded that the environmental impact of the electrolytic hydrogen production process is mainly caused by the GWP of the electricity supply. For future environmental impact studies on hydrogen production systems, it is highly recommended to 1) divide the whole system into well-defined subsystems using compression as the final stage of the LCA and 2) to provide energy inputs/GWP results for the different subsystems.

In this work, ultra-thin n-type hydrogenated nanocrystalline silicon oxide [(nc-SiOx:H (n)] film was used to replace amorphous silicon [a-Si:H (n)] as electron transport layer (ETL) in rear-junction silicon heterojunction (SHJ) solar cell to reduce front parasitic absorption. The contact resistivity between the transparent conductive oxide (TCO) and ultra-thin ETL interface plays an important role on the cell performance. A nanocrystalline silicon (nc-Si:H) contact or seed layer was introduced in the solar cell with ultra-thin nc-SiOx:H and the impact of the nc-Si:H thickness on the cell performance was investigated. To demonstrate scalability, bifacial solar cells with 10 nm ETL were fabricated on the M2 (244 cm2) wafer. The best cell performance is obtained by the solar cell with 5 nm nc-SiOx:H (n) and 5 nm nc-Si:H (n) contact layer and it exhibits open-circuit voltage (Voc) of 738 mV, fill factor (FF) of 80.4%, short-circuit current density (Jsc) of 39.0 mA/cm2 and power conversion efficiency (η) of 23.1% on M2 wafer. Compared to the one with nc-SiOx:H (n), an increase of 3%abs of FF and 0.5%abs of η and lower front contact resistivity is demonstrated for the solar cells with nc-Si:H (n) / nc-SiOx:H (n) double layer, which is caused by the lower energy barrier for electrons, according to the band diagram calculated by the AFORS-HET simulator. A simulation on the solar cell optical and electrical losses was done by the Quokka 3 simulator and shows much lower electrical transport loss and a bit higher front surface transmission loss for the one with double layer than nc-SiOx:H (n) single layer.

The surface patterning of Si heterojunction solar cells is of key importance to enhance the light trapping properties and enable high efficiencies of the emerging thin crystalline silicon solar cells. Herein, periodic inverted pyramids with different periodicity patterns were fabricated by nanoimprint lithography in combination with dry- and wetetching techniques. The impact of their periodicity on the light trapping properties was studied by measuring their reflectance and photoluminescence properties. The inverted pyramids with 700 nm periodicity show excellent anti-reflection and selective light-trapping properties.

Light trapping in crystalline silicon (c-Si) solar cells is an essential building block for high efficiency solar cells targeting low material consumption and low costs. In this study, we present the successful implementation of highly efficient light-trapping back contacts, subsequent to the passivation of Si heterojunction solar cells. The back contacts are realized by texturing an amorphous silicon layer with a refractive index close to the one of crystalline silicon at the back side of the silicon wafer. As a result, decoupling of optically active and electrically active layers is introduced. In the long run, the presented concept has the potential to improve light trapping in monolithic Si multijunction solar cells as well as solar cell configurations where texturing of the Si absorber surfaces usually results in a deterioration of the electrical properties. As part of this study, different light-trapping textures were applied to prototype silicon heterojunction solar cells. The best path length enhancement factors, at high passivation quality, were obtained with light-trapping textures based on randomly distributed craters. Comparing a planar reference solar cell with an absorber thickness of 280 μm and additional anti-reflection coating, the short-circuit current density (JSC) improves for a similar solar cell with light-trapping back contact. Due to the light trapping back contact, the JSC is enhanced around 1.8 mA cm−2 to 38.5 mA cm−2 due to light trapping in the wavelength range between 1000 nm and 1150 nm.

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.

Nanophotonic light management concepts are essential building blocks of advanced thin-film solar cells. These concepts make use of light coupling to waveguide modes that are supported by the photoactive absorber material of the solar cell. In a recent study, we presented a new method based on scanning near-field optical microscopy that enables the direct nanoscale investigation of light coupling to an individual waveguide mode in a nanophotonic thin-film silicon solar cell. Making use of this method, we investigate in this contribution the polarization dependence of the light coupling to a waveguide mode. Based on this polarization dependence, we can attribute the investigated waveguide mode to a transverse electric mode. Moreover, we identify the grating vector, which is responsible for the light coupling to the investigated waveguide mode in the nanopatterned thin-film silicon solar cell.

An aperture-type scanning near-field optical microscope (a-SNOM) is readily used for the optical and optoelectronic characterizations of a wide variety of chemical, biological and optoelectronic samples with sub-wavelength optical resolution. These samples mostly exhibit nanoscale topographic variations, which are related to local material inhomogeneity probed either by an optical contrast or by secondary effects such as photoconductivity or photoluminescence. To date, in the interpretation and evaluation of the measurement results from a-SNOM or derived methods, often only the local material inhomogeneity is taken into account. A possible influence of the optical interaction between the scanning probe and the surface topography is rarely discussed. In this paper, we present experimental and theoretical investigation of the effects of nanoscale topographic features on a-SNOM measurement results. We conduct local photocurrent measurements on a thin-film solar cell with an a-SNOM as the illumination source. A clear correlation between the photocurrent response and local topography is observed in all measurements with a signal contrast of up to ∼30%, although the sample features homogeneous permittivity and electrical properties. With the help of finite-difference time-domain (FDTD) simulations, this correlation is reproduced and local light coupling is identified as the mechanism which determines the local photocurrent response. Our results suggest that a-SNOM-based measurements of any sample with material inhomogeneity will be superimposed by the local light-coupling effect if surface topography variation exists. This effect should always be taken into consideration for an accurate interpretation of the measurement results.

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 SnO 2 :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.

Impact of periodicity was studied for micro- and nano-pyramids fabricated by low-cost nanoimprint lithography process. Investigations by photoluminescence imaging displayed excellent anti-reflection and wavelength-selective light-trapping properties.

Light scattering OLED substrates relying on disordered self-assemblies are fabricated by microsphere and polymer blend lithography and used for light extraction. We report on a device efficiency enhancement of up to 50 %.

Thin-film silicon solar cells often rely on a metal back reflector separated from the silicon layers by a thin rear dielectric as a back reflector (BR) design. In this work, we aim to obtain a better insight into the influence of the rear-dielectric/Ag BR design on the optical performance of hydrogenated microcrystalline silicon (µc-Si:H) solar cells. To allow the application of a large variety of rear dielectrics combined with Ag BRs of diverse topographies, the solar cell is equipped with a local electrical contact scheme that enables the use of non-conductive rear dielectrics such as air or transparent liquids of various refractive indices n. With this approach, detached Ag BRs having the desire surface texture can be placed behind the same solar cell, yielding a direct and precise evaluation of their impact on the optical cell performance. The experiments show that both the external quantum efficiency and the device absorptance are improved with decreasing n and increasing roughness of the BR. Calculations of the angular intensity distribution of the scattered light in the µc-Si:H are presented. They allow for establishing a consistent picture of the light trapping in the solar cell. Copyright © 2013 John Wiley & Sons, Ltd.

We present three different working modes of scanning near-field optical microscopy which provide complementary information about the electro-optical properties of solar cells. Those working modes allows to study the local light scattering and trapping in textured solar cells, the local light propagation inside the cell and the impact of lateral inhomogeneity on a nanoscopic scale. Due to the presence of evanescent light modes, the presented techniques give access to important physical effects which is only possible in the optical near-field.

In the present work, we investigate light-management concepts applied subsequent to the passivation of the Si wafer of planar Si heterojunction solar cells. As a first concept, we apply amorphous silicon based nanophotonic textures at the back side of the Si wafer to realize efficient light trapping. As a second concept, we use a nanoimprint lithography based front side anti-reflection coating to improve the incoupling of light into the solar cell absorber. Both concepts allow for efficient improvements in the short-circuit current densities without degrading the planar passivation layers. As the highlight of this work, we demonstrate planar silicon heterojunction solar cells (thickness ∼ 280 μm) with high passivation quality as well as a short-circuit current density of 38.8 mA/cm2.

In thin-film silicon solar cell devices randomly textured interfaces are used to achieve light scattering sufficient for efficient light trapping. We use near-field scanning optical microscopy (NSOM) for visualizing wave guiding mechanisms experimentally by measuring the evanescent modes. Their impact on the light trapping efficiency and the link to topographic structures will be addressed.

Light scattering at randomly textured interfaces in tandem solar cells consisting of hydrogenated amorphous silicon (a-Si:H) and hydrogenated microcrystalline silicon (μc-Si:H) is studied in the optical near-field experimentally by near-field scanning optical microscopy (NSOM) and theoretically by a rigorous solution of Maxwell's equations using a Fourier ansatz. The work concentrates on the influence of evanescent light modes on the absorption in the a-Si:H top cell. It is found that the improvement of solar cell efficiency due to the surface texturing is borne by evanescent light modes. For both, the theoretical and the experimental study, techniques are developed to extract the evanescent part of the light from the obtained data. From the theoretical results, the principal mechanism of light scattering in the optical near-field regime is studied and, in particular, light which is trapped in the a-Si:H top cell by total internal reflection is visualized. From the experimental results, a map of the local light trapping efficiency is generated and the correlation to morphological properties is studied.

Light trapping in thin-film silicon solar cell arising from randomly textured ZnO front contact layers is investigated in the optical near-field experimentally and theoretically. The experimental data are obtained from near-field scanning optical microscopy, theoretical data are calculated using rigorous diffraction theory. The surface of the randomly textured ZnO consists of statistically distributed craters with different shapes. Along the rims of the craters light localizations are found. Photon jets emerge from the vertices of the surface profile. From the theoretical study, the local absorption enhancement is calculated. The results provide important insight into the local effects of light trapping in thin-film optoelectronic devices and strategies for optimizing the external quanturn efficiency in thin-film silicon solar cells are discussed.

The electric field intensity above the surface of opal photonic crystals (PCs) and its alteration due to ‘crystallographic’ defects is investigated by using near-field scanning optical microscopy (NSOM). The photonic crystals are developed by dip coating in a liquid solution with PMMA opals. Highly regular hexagonal planes with lattice constants of about 260 nm grow on the glass substrate. During the drying process several crack lines are formed that correspond to defects in the crystal structure. The transmitted light intensity at wavelengths inside and outside of the stop band of the PC is studied with NSOM using a tapered fiber tip scanning in all three dimensions. By this technique, a 3D image of the electric field intensity can be measured with a resolution better than 100 nm. The results show that the local optical field distribution is strongly dominated by the defect states in all directions in space over a length scale of several μm. Above the crack lines, the intensity of light is strongly reduced. Beams of light are observed emerging from the edges of the crack lines and propagate in air with heights of more than 3 μm. In between two different crack lines, periodic repetitions of the beams are observed. These results are interpreted as light diffraction on a microscopic scale.

We report on near-field scanning optical microscopy measurements on randomly textured ZnO thin films. These films are commonly used as transparent conducting oxide in thin-film solar cells. Textured interfaces are used to increase the scattering of light, which leads to a better light trapping in the solar cell. Here, both the topography and the local transmission are measured with a tapered fiber tip with very high spatial resolution. By varying the distance of the tip and the wavelength of the incident light, the optical profile is visualized and reveals a strong confinement of light on a subwavelength scale which corresponds to ridges in the surface structure. The confinement of light results from guided optical modes in the ZnO which are accompanied by a modulated evanescent field in air. No corresponding structure to this modulation is found in the topography. These results give new insight for further improvement of light trapping in solar cells.

Nanophotonic light management concepts are essential building blocks of advance photovoltaic technologies. These concepts make use of light coupling to waveguide modes supported by the photoactive absorber material of the solar cell. In this contribution, we will explain on the basis of our recently published results the development of scanning near field optical microscopy as a new method that enables the direct nanoscale observation of light coupling to an individual waveguide mode in a nanophotonic thin-film silicon solar cell. Beyond this, we present a new detailed study based on this new method on the polarization dependence of the light coupling to an individual waveguide mode.

Cellulose substrates for PV applications present a fibrous surface texture that is not suitable for the uniform deposition of thin-film solar cells causing poor device performance. However, uniform thin-film deposition and efficient light management for solar cells can be achieved on cellulose substrates by transferring well-known surface textures that provide an adequate surface for thin film solar cell deposition and also, provide light scattering properties into the cellulose surface. In this work, we study the properties of crater-like textures transferred onto cellulose substrates by nanoimprint lithography and the corresponding effect on the J–V and EQE characteristics of amorphous silicon thin-film solar cells. The prototype solar cells are deposited on cellulose substrates and the results are compared with the results of such solar cells deposited on flat glass substrates. The results show that the J–V characteristics of solar cells deposited on planar as well as textured glass substrates are well reproduced. Due to the process routine, the solar cells on the cellulose substrate with nanoimprinted textures show an increase in the short circuit current density and power conversion efficiency over previous results in our laboratory.

We investigate light-scattering textures for the application in thin-film solar cells which consist of a random texture, as commonly applied in thin-film solar cells, that are superimposed with a two-dimensional grating structure. Those textures are called photonic random texture. A scalar optical model is applied to describe the light-scattering properties of those textures. With this model, we calculate the angular resolved light scattering into silicon in transmission at the front contact and for reflection at the back contact of a microcrystalline silicon solar cell. A quantity to describe the light- trapping efficiency is derived and verified by rigorous diffraction theory. We show that this quantity is well suitable to predict the short-circuit current density in the light-trapping regime, where the absorptance is low. By varying the period, height and shape of the unit cell, we optimize the grating structure with respect to the total generated current density. The maximal predicted improvement in the spectral range from 600-900 nm is found to be about 3 mA/cm² compared to the standard random texture and about 6 mA/cm² compared to a flat solar cell. Different light-trapping concepts were applied in silicon-based thin-film solar cells to overcome the limitations due to the low absorptance near the band gap for flat devices 1,2 and the limited device thickness due to light-induced degradation. Differently textured interfaces improve light coupling into the absorber material and provide light guidance in the layer. Mostly, random textures were incorporated that scatter incoming light diffusely prolonging the effective light path. 3-6 Recent work was done by several groups where periodic structures, e.g. gratings or photonic crystals, were incorporated at different interfaces of the device. 7-12 The complex surface structures demand for rigorous optical models with high computational effort and huge memory in order to describe their impact on light absorption. With such models, optimizations are only possible in strictly limited parameter spaces to fix into computer capacities availably nowadays. We recently demonstrated that the angular resolved scattering in transmission and reflection inside the silicon absorber material can be sufficiently described by a simple scalar approach. 13-15 This simple model allows optimization of the interface structure in a huge parameter space with low computational effort. We found that the amount of light scattered beyond the critical angle of total internal reflection correlates nicely to the external quantum efficiency. Therefore, this investigation was done in the spectral range, where light trapping is mostly efficient (600-900 nm) and the short-circuit current density was derived for this spectral range (jsc,600-900). We interpret this quantity as a benchmark for the efficiency of the light-trapping texture and carry out the optimum. In this work, we investigated in detail the combination of both, random texture and periodic structure. Starting with a randomly textured ZnO:Al layer, that is well-known to provide high-efficiency microcrystalline silicon (µc-Si:H) solar cells, we superimposed a two-dimensional periodic structure with optimized period and height to the random texture. The design of the structure was done by applying the scalar approach. Our results from the simple scalar approach were verified by Finite-Difference Time-Domain (FDTD) simulations of the real layer stack for selected structures. In detail, we optimized the period and height of different unit cell geometries. Those gratings were applied to flat interfaces, leading to photonic textures, and the randomly textured ZnO:Al layer, leading to photonic random textures. The jsc,600-900 for the flat and random reference cell were found to be 6.48 mA/cm² and 9.32 mA/cm², respectively. The largest short-circuit current density we found is jsc,600-900=12.40 mA/cm². This is an improvement of about 6 mA/cm² compared to the flat cell and still about 3 mA/cm² compared to the standard random texture.

In this study, light propagation in textured hydrogenated microcrystalline silicon (μc-Si:H) thin-film solar cells is investigated on a sub-micron-scale by means of dual-probe scanning near-field optical microscopy (SNOM). Applying advanced modes of operation - exclusively available at dual probe SNOMs - light propagation is analyzed with subwavelength resolution. Measurements at μc-Si:H thin-film solar cells layer are presented visualizing the influence of local surface features on light propagation. Furthermore, the intensity decay of light guided inside the solar cell is mapped. The observed intensity decay agrees well with theory, verifying the validity of the method.

Periodic or random nanostructures in thin-film solar cells at the front, rear and as interlayer enhance solar cell efficiencies. The underlying effect of dielectric or plasmonic light scattering will be discussed combining experiments and theory.

The scattering of light by the textured transparent conductive oxide (TCO) in thin-film silicon solar cells is frequently described by transmission haze and angular intensity distribution (AID) at the interface between the TCO and air. The scattering is expected to improve the light trapping and, therefore, the absorption of the solar cell. Using these scattering properties as input parameters for the electrical modeling of thin-film solar cells leads to significant deviations from the measurements for short circuit current densities. The major disadvantage of the AID measurement at the TCO/air interface is that in real thin-film silicon solar cells the TCO/Si interface is relevant. We use a model that is based on scalar scattering theory to calculate the scattering properties at the transition into air and into silicon. The model takes into account the measured surface topography and the optical constants of the adjacent media. For a series of μc-Si:H cells on ZnO:Al with different surface topographies, AID and the transmission haze into a μc-Si:H half space are calculated. From these results, a quantity is derived that describes the scattering efficiency. This quantity is compared to the short circuit current densities of μc-Si:H solar cells showing good agreement. It will be shown that for artificially modified textures an increase in the short-circuit current density and thus, the efficiency of thin-film silicon solar cells can be achieved.

In order to obtain efficient light trapping within a thin-film silicon solar cell, randomly textured interfaces are used. The texture can be introduced by wet-chemical etching in diluted hyrdofluoric acid (HF). By varying of the HF concentration, a continuous transition to smaller surface structures can be achieved. Near-field scanning optical microscopy is applied to measure scattered light with sub-wavelength resolution. On those different surfaces, using Fourier high-pass filters on the measured near-field images, surface features with a high light trapping potential are identified. Finally, criteria for optimized scattering surfaces are obtained.

We analyze the absorption enhancement in single and tandem solar-cells comprising nanostructures that increase the path of the photons inside the solar cell. For this purpose we exploit different physical phenomena in different material systems.

Randomly textured zinc oxide surfaces with and without amorphous silicon deposited on top are studied by near-field scanning optical microscopy. By virtue of a three dimensions it allows to access the local light intensity in the entire spatial domain above the structures. Measurements are compared with large scale finite-difference time-domain simulations. This study provides new insight into light trapping in thin-film silicon solar cells on a nanoscopic scale. Light localization on the surface of the textured interface and a focusing of light by the structure further away are observed as the key features characteristic for such surfaces.

We report on nano-scale optical effects of amorphous silicon layer conformally deposited on randomly textured zinc oxide layers on glass substrates investigated by near-field scanning microscopy. Such textured layers are used in thin-film photovoltaic devices to enhance light trapping. Experimental results are compared to theoretical data, obtained from large scale finite-difference time-domain simulations. Light localization on the surface of the textured interface and a focusing of light by the structure further away are observed. The measurements are compared with simulations, which provide additional insight into the light intensity distribution inside the solar cell on a nm-scale. It will be shown how this information can be used to optimize light trapping in thin-film solar cells using an amorphous silicon solar cell as an example.

By using a rigorous diffraction theory, the localization of light near textured zinc oxide (ZnO) surfaces is theoretically investigated and compared with experimental data obtained from scanning-near-field-optical microscopy. Although random by nature, these surfaces show well-defined geometrical features, which cause the formation of localized light patterns near the surface. Particularly, photon jets are observed to emerge from conical surface structures. Because these structures are of primary importance for applications in photovoltaics, we analyze the "real" surface topography of textured ZnO used in silicon solar cells. With this work, valuable insight is provided into the mechanism of light coupling through randomly textured interfaces. (C) 2007 American Institute of Physics.

We experimentally investigate the light-trapping effect of plasmonic reflection grating back contacts in prototype hydrogenated amorphous silicon thin-film solar cells in substrate configuration. These back contacts consist of periodically arranged Ag nanostructures on flat Ag reflectors. We vary the period, unit cell, and width of the nanostructures to identify design strategies for optimized light trapping. First, a general correlation between the reduction of the period of the nanostructures down to 550 nm and an increase of the absorptance, as well as external quantum efficiency is found for various unit cells formed by nanostructures. Second, increasing the width of the nanostructures from 200 to 350 nm, an enhanced light-trapping effect of the thin-film solar cells is found independent of the period. As a result, we identify a design for improved light trapping for the given solar cell parameters within the considered variations. It consists of thin-film solar cells applying a combination of a period of 600 nm and a structure width of 350 nm. The implementation of back contacts with this configuration yields enhanced power conversion efficiency as compared to reference solar cells processed on conventionally used randomly textured substrates. In detail, the enhancement of the short-circuit current density from initially 14.7 to initially 15.6 mA/cm2 improves the power conversion efficiency from 9.1 to 9.3%.

Using rigorous diffraction theory we investigate the scattering properties of various random textures currently used for photon management in thin-film solar cells. We relate the haze and the angularly resolved scattering function of these cells to the enhancement of light absorption. A simple criterion is derived that provides an explanation why certain textures operate more beneficially than others. Using this criterion we propose a generic surface profile that outperforms the available substrates. This work facilitates the understanding of the effect of randomly textured surfaces and provides guidelines towards their optimization.