We present a critical review on optical research in photovoltaics guided by the question: Which topics do we regard as most relevant to accelerate the large-scale implementation of photovoltaics? The following areas were identified: 1) The development of high-performance earth-abundant solar cell materials and the reduction of indium and silver in the device. 2) Color concepts for an appealing optical appearance of solar modules as photovoltaic modules enter urban environments as well as agricultural areas on a large scale. 3) Optical optimization of multijunction solar cells based on perovskite, III-V semiconductors and silicon to overcome the single-junction efficiency limit. 4) Accurate energy yield predictions considering the full complex illumination conditions particularly regarding bifacial and multijunction solar cells. 5) Advanced concepts with strong momentum such as radiative cooling and spectral conversion.

To achieve optimal optical performance and minimal reflection losses, a textured interface between perovskite and silicon sub-cells in perovskite-silicon tandem solar cells is needed. However, the perovskite solar cells fabrication method yielding the highest efficiencies, spin coating, is not compatible with the conventional random micro-pyramidal texture on silicon. This study focuses on creating periodic inverted micro-pyramidal textures in silicon through photolithography, reactive ion etching, and wet-chemical etching, enabling the deposition of fully textured perovskite solar cells with low reflectance on the textured silicon via spin-coating. This breakthrough lays the foundation for the fabrication of optically and electronically optimized perovskite-silicon tandem solar cells.

Dedicated optical models are crucial for advancing the modelling of next-generation solar cells. Incorporating various textures of different shapes and sizes into solar cells significantly improves light management. This study optimizes the optical design and predicts the performance of a novel thin-film tandem solar cell device. The top cell features a hydrogenated amorphous silicon (a-Si:H) absorber layer, while the bottom cell incorporates a low-bandgap tin-lead-based perovskite (Sn-Pb PVK) absorber layer, all supported on a flexible aluminum substrate Optical simulations exhibit 24 mA/cm² as total implied photo-current density when the absorber layer thicknesses are current-matched. The maximum absorptance reaches 80% at 500 nm for a-Si:H and only 62% at 800 nm for Sn-Pb PVK sub-cells. Experimental results show open-circuit voltages of 0.9 V for a-Si:H and 0.85 V for Sn-Pb PVK solar cells. Based on the highest achieved fill factor of 0.77, the researchers estimated a power conversion efficiency exceeding 16%.

In this contribution we study numerically, how sinusoidal nanotextures would affect the (optical) performance of all-perovskite tandem solar cells. The simulations are conducted with the finite element method (FEM) and consider solar cells in glass superstrate configuration. We correct for the multiple interactions between light that is reflected from the solar cell stack and the glass-air interface with an iterative scattering-matrix approach. To achieve current matching, we optimize the perovskite thickness of the top cell using the Newton method. Results show that front texturing improves the photocurrent density with respect to the planar reference. Additional texturing between top and bottom cell hardly improves the performance. Full texturing leads to an increased photocurrent density, which can mostly be attributed to light trapping at the absorption edge of the bottom cell. Our study shows how texturing can help to further increase the efficiency of all-perovskite tandem solar cells.

Glass textures can fulfil various effects in photovoltaic (PV) modules: enhanced in-coupling for large incidence angles, glare reduction or color appearance with high angular tolerance. These effects are of particular interest for integrated PV (e.g. building or vehicle integration). This overview will describe the texture dependent effects, give design guidelines, describe industrial texturing technologies and show exemplary results.

Color aesthetics in photovoltaic modules are essential, especially in design-sensitive applications like building integrated photovoltaics (BIPV). Distributed Bragg reflector-based color filters can modify the appearance of silicon solar cells. This study extends the aesthetic evaluation to emerging perovskite solar cells, typically gray-brown, by integrating them with a MorphoColor® color filter. We present simulated and measured angular resolved reflectance measurements and evaluate the color appearance from varied viewing angles. The used simulation environment is based on wave optics and raytracing. Next, we study the impact of individual layer parameters on the color appearance and the maximum achievable short circuit current density in the perovskite solar cell. Findings show that changes in color filter-perovskite interfacing layers influence the saturation and hue of the color impression as well as the angular color stability. Finally, we present initial concepts of optimizing the specific layer stack, demonstrating its potential to tailor a customized color design.

The MorphoColor concept makes use of multilayer and structure interaction for colored photovoltaic (PV) modules. The photonic effect, inspired by the Morpho butterfly's wing, is optimized to produce saturated colors, a high angular tolerance of the color appearance and to maintain a very high module efficiency. This concept, implemented on textured glass surfaces, has already been applied to integrated photovoltaic modules. As a further development, we investigated implementing the MorphoColor interface on a polymeric film which then can be integrated into a PV module. This MorphoFlex concept enables twofold flexibility: for the production process as well as for curved modules. We will present the process chain for the film structuring, coating and integration, first results on film and module level, and show demonstrators.

Dielectric metasurfaces with tailored disordered have recently emerged as a highly favored light-trapping approach for solar cells compared to traditional techniques like direct nanostructuring and antireflective (AR) coatings. The research interest is due to their superior light-scattering properties, ideal for thin solar cells. Moreover, they successfully overcome the detrimental impact on electrical performance due to texturing and can be produced on macroscopically large wafers using self-assembly nanofabrication methods. This work investigates a graded-index-based design strategy for such disordered metasurfaces where the disordered arrangement is tailored towards a correlated, hyperuniform disorder. Individual scattering elements are designed by drawing inspiration from transformation optics. We numerically and experimentally demonstrate that our disordered graded-index metasurface can significantly improve the light-trapping and antireflective performance of a solar cell stack, especially when compared to structures that implement only one of the two design strategies.

Computational design of perovskite based solar cell devices with enhanced power conversion efficiency. The designs reflect efficient trapping of incident electromagnetic waves.

Solar cells based on perovskite compounds have displayed remarkable efficiency, with a focus on enhancing parameters like short-circuit current (Jsc) and open-circuit voltage (Voc) to maximize their performance. However, Voc is closely related to recombination and optical effects and is an important parameter affecting energy conversion efficiency. To exploit the full potential of perovskite solar cells, photonic management emerges as a key strategy. This study delves into the optical strategies for improving the open-circuit voltage (Voc) and overall efficiency of perovskite solar cells.

We report a light-induced oxyhydroxides-alloy heterostructure reconfigured from a nickel-iron alloy film as a highly catalytic and protective layer on photoanodes for solar water oxidation. The optimized photoanodes exhibit a high applied bias photon-to-current efficiency of 4.24% and long-term stability beyond 250 hours, outperforming the closest competitors by 330% in efficiency and 408% in stability, respectively. This self-generated catalytic-protective oxyhydroxides-alloy layer coating strategy opens the way to implementing large scalable photoelectrochemical devices for solar fuel production with high efficiency and device lifetime.

As solar cells from direct semiconductors improve, i.e. become more radiative, luminescent coupling becomes more and more relevant. This has a strong impact on artifacts in EQE measurements of multi-junction solar cells, which e.g. is a challenge, when characterizing III-V//Si multi-junction solar cells. By measuring the response of these cells under varying illumination conditions, this effect can be understood and EQE measurements can be corrected.

This study introduces an optical approach to enhance the open-circuit voltage (Voc) in organic solar cells (OSCs) characterized by high radiative recombination. By exploring various one-dimensional structurations of the OSC device, we reduce Boltzmann losses arising from the mismatch between absorption and emission cones. This innovative method leads to a significant Voc enhancement, achieving an increase of approximately 30 mV through optical means. Furthermore, our findings establish a novel route in the development of planar geometry single-junction solar cells, surpassing the power conversion efficiency values set by the Shockley-Queisser limit.

Here, is presented the impact of pristine graphene, used as additive in the active layer or as substrate, in Lead Halide Perovskites based Solar Cells and LEDs. A small concentration of graphene nanoplatelets, well above the percolation threshold, either in the PEDOT:PSS hole transport layer or in the MAPbI3 active layer of a SC produces structural changes that improve both the efficiency and the stability of the device. Similarly, adding graphene in MAPbBr3 active layer of LEDs lead to larger grain domain sizes and increased luminance. Finally, for MAPbBr3 thin films grown directly on substrates of graphene/graphene oxide, the concentration of the precursor solution and the nature of the substrate lead to a continuous film, or dispersed particles of nano-to-micrometer sizes. The crystal size and microstrain determines the emission properties, showing hugely enhanced photostabilities compared to MAPbBr3 on glass, capable of enduring light densities up to > 100 kW/cm2 for several minutes. These results open new opportunities for the design of nanoengineered photovoltaic devices based on combined graphene/perovskites with improved stability and performance.

The exceptional magnetic, electrical, and optical properties exhibited by metal halide perovskites (MHPs) have garnered significant interest from the optoelectronic research community in recent decades. Perovskite solar cells (PeSCs) have gained substantial attention due to their inherent advantages, such as solution processability, tunable band gaps, high absorption coefficients, and long carrier diffusion lengths. To optimize the performance and stability of PeSCs, it is crucial to incorporate appropriate charge transport layers (CTLs) and/or interlayers. These CTLs need to possess suitable energy levels for efficient charge injection and transport, while effectively blocking opposite charges. Additionally, the CTL located beneath the perovskite layer plays a critical role as it significantly influences the crystal growth of the perovskite layer and affects the presence of interfacial defects. In this presentation, a new series of conjugated polyelectrolytes (CPEs) will be introduced as ideal interfacial layers and CTLs for various PeSCs devices.