We present a highly efficient monolithic perovskite/silicon tandem solar cell and analyze the tandem performance as a function of photocurrent mismatch with important implications for future device and energy yield optimizations.

Perovskite–silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite–silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%.

will enable fully textured perovskite/silicon tandem solar cells by co-evaporation that are on par with state-of-the-art devices employing solution-processed perovskites.

For methylammonium lead iodide perovskite solar cells prepared by co-evaporation, power conversion efficiencies of over 20% have been already demonstrated, however, so far only in n-i-p configuration. Currently, the overall major challenges are the complex evaporation characteristics of organic precursors that strongly depend on the underlying charge selective contacts and the insufficient reproducibility of the co-evaporation process. To ensure a reliable co-evaporation process, it is important to identify the impact of different parameters in order to develop a more detailed understanding. In this work, we study the influence of substrate temperature, underlying hole transporting material (polymer PTAA versus self-assembling monolayer molecule MeO-2PACz) and perovskite precursor ratio on the morphology, composition and performance of co-evaporated p-i-n perovskite solar cells. We first analyse the evaporation of pure precursor materials and show that the adhesion of methylammonium iodide (MAI) is significantly reduced with increased substrate temperature, while it remains almost unaffected for lead iodide (PbI2). This substrate temperature-dependent evaporation behaviour of MAI is also transferred to the co-evaporation process and can directly influence the perovskite composition. We demonstrate that the optimal substrate temperature window for perovskite deposition is close to room temperature. At high temperature not enough MAI for precise stoichiometry is incorporated even with very high MAI rates While at temperatures below -25 °C the conversion of MAI with PbI2 is inhibit and an amorphous yet unreacted film is formed. We observe that perovskite composition and morphology vary widely between the organic hole-transport layer (HTLs) PTAA and MeO-2PACz. For all substrate temperatures MeO-2PACz enables higher solar cell PCEs than PTAA. Through the combination of vapourdeposited perovskites and self-assembled monolayer, we achieve a stabilised power conversion efficiency of 20.6 %, which is the first reported PCE above 20% for evaporated perovskite solar cells in p-i-n architecture.

We present a three-terminal (3T) tandem approach for the interconnection of a perovskite top cell with an interdigitated back contact (IBC) silicon heterojunction (SHJ) bottom cell. The general viability of our cell design is further verified with drift-diffusion simulations indicating efficient charge carrier transport throughout the whole device and an efficiency potential of ≈27% using readily available absorber and contact materials. Our experimental proof-of-concept device reaches a combined PCE of 17.1% when both subcells are operating at their individual maximum power point. To emulate different operation conditions, the current-voltage characteristics of both cells were obtained by measuring one subcell while the other cell was set to a fixed bias voltage. Only a slight mutual dependence of both subcells was found. As determined by electrical simulations, it likely stems from the resistance of the electron contact on the cell's rear side, which is shared by both subcells. The optimisation of this contact turns out to be a major design criterion for IBC 3T tandems. We demonstrate that our current proof-of-concept cells are limited by this series resistance as well as by optical losses, and we discuss pathways to approach the simulated efficiency potential by an optimised device design.