Harnessing Lead-free Rb₃Sb₂I₉ Perovskite Derivative Towards Higher Photovoltaic Performance

Lead-halide perovskites boast outstanding optoelectronic properties,extremely attractive,for instance,for solar harvesting.However,they are characterized by limited stability and substantial toxicity,which limits their commercial deployment.Recently,a promising route for lead replacement has come to the fore,which involves the use of antimony.The potential of antimony-based perovskites(ABPs)follows from preliminary indications on their superior stability with respect to the lead-based counterparts,and their similarity in terms of magnitude of the absorption coefficient and character of the frontier energy bands.While ABP performance reported to date has been unsatisfactory,the preliminary stage of the studies so far suggests that their potential is yet to be fully unraveled,particularly in relation to film morphology and interfaces.In this work,we focus on a special Sb-based perovskite,Rb3Sb2I9,which is particularly attractive due to its higher-dimensionality(2D)than other ABPs synthesized to date.Aiming towards higher photovoltaic performance,we explore different deposition strategies towards higher-quality films,and different transport layers towards superior charge extraction.In particular,our work consists of the following parts:1.Extensive study of different processing methods aiming to increase the grain size of Rb3Sb2I9 thin films.These methods rely on either a supersaturation-controlled strategy or on SbI3-vapor-assisted high-temperature annealing.The resulting thin films are characterized in terms of absorption,structure,and energy levels.2.Experimental assessment of Rb3Sb2I9 solar cell performance using the range of thin-film deposition conditions developed within this work.We find that the photoelectric conversion efficiency reaches up to 1.35%,which is the highest reported to date for Rb3Sb2I9 thin film solar cells.Additionally,we address the challenge posed by the high-lying conduction band of Rb3Sb2I9,and explore different strategies to improve electron extraction(work function tuning with PEIE and self-assembled monolayers,and doped metal-oxide electron transport layer with adjusted work function).3.Analysis of spectral and voltage dependence of the photocurrent in Rb3Sb2I9 solar cells.We obtain insight into the functioning of our ABP devices by relating the observed solar cell performance to their external and internal quantum efficiencies(EQE and IQE),and by analyzing the voltage dependence of the photocurrent.