91̽��

Abstract:

Narrow bandgap lead-tin perovskites are essential components of next-generation all-perovskite multi-junction solar cells. However, their poor stability under operating conditions hinders successful implementation. In this work, we systematically investigate the underlying mechanisms of this instability under combined heat and light stress (ISOS L-2 conditions) by measuring changes in phase, conductivity, recombination and current-voltage characteristics. We find an increased impact of the redistribution of mobile ions during device operation to be the primary driver of performance loss during stressing, with further losses caused by a slower increase in non-radiative recombination and background hole density. Crucially, the dominant degradation mode changes with different hole transport materials, which we attribute to variations in iodine vacancy generation rates. By quantifying the impact of these mechanisms on device performance, we provide critical insights for improving the operational stability of lead-tin perovskite solar cells.

Abstract:

Doping with small densities of foreign ions is an essential strategy for tuning the optoelectronic properties of semiconductors, but the effects of doping are not well-understood in halide perovskites. We investigate the effect of Bi3+ and Sb3+ doping in lead–tin perovskites. Films doped with small amounts of BiI3 and SbI3 show greatly increased non-radiative recombination at precursor doping concentrations as low as 1 ppm for Bi3+ and 1000 ppm for Sb3+. We rationalize such behaviour by density functional theory (DFT) simulations, showing that these metal ions can be incorporated in the perovskite crystal by introducing deep trap levels in the band gap. Having found that very small amounts of Bi3+ greatly reduce the optoelectronic quality of lead–tin perovskite films, we investigate the presence of Bi impurities in perovskite precursor chemicals and find quantities approaching 1 ppm in some. In response, we introduce a facile method for removing Bi3+ impurities and demonstrate removal of 100 ppm Bi from a perovskite ink. This work demonstrates how the incorporation of small concentrations of foreign metal ions can severely affect film quality, raising the importance of precursor chemical purity.

Abstract:

In this work we demonstrate that time-resolved photoluminescence data of metal halide perovskites can be effectively evaluated by combining Bayesian inference with a Markov-Chain Monte-Carlo algorithm and a physical model. This approach enables us to infer a high number of parameters which govern the performance of metal halide perovskite-based devices, alongside the probability distributions of those parameters, as well as correlations among all parameters. Via studying a set of "half-stacks’‘, comprising electron and hole transport materials contacting perovskite thin-films, we determine surface recombination velocities at these interfaces with high precision. From the probability distributions of all inferred parameters, we can simulate intensity-dependent photoluminescence quantum efficiency and compare it to the experimental data. Finally, we estimate mobility values for the "vertical’’ charge carrier transport, that perpendicular to the plane of the substrate, for all samples using our approach. Since this mobility estimation is derived from charge carrier diffusion over the length-scale of the film thickness and in the vertical direction, it is highly relevant to transport in photovoltaic and light emitting devices. Our approach of coupling spectroscopic measurements with advanced, computational analysis will help speed up scientific research in the field of optoelectronic materials and devices and exemplifies how carefully constructed computational algorithms can derive valuable plurality of information from simple datasets. We expect that our approach will be expandable to a variety of other analysis techniques and that our method will be applicable to other semiconductors.

Abstract:

Abstract:

Silver‐bismuth‐based perovskite‐inspired materials (PIMs) are increasingly being explored as non‐toxic materials in photovoltaic applications. However, many of these materials exhibit an ultrafast localization of photogenerated charge carriers that is detrimental for charge‐carrier extraction. In this work, such localization processes are explored for thermally evaporated thin films of compositions lying along the (AgI)x(BiI3)y series, namely BiI3, AgBi2I7, AgBiI4, Ag2BiI5, Ag3BiI6, and AgI, to investigate the impact of changing Ag+/Bi3+ content. A persistent presence of ultrafast charge‐carrier localization in all mixed compositions and BiI3, together with unusually broad photoluminescence spectra, reveal that eliminating silver will not suppress the emergence of a localized state. A weak change in electronic bandgap and charge‐carrier mobility reveals the resilience of the electronic band structure upon modifications in the Ag+/Bi3+ composition of the mixed‐metal rudorffites. Instead, chemical composition impacts the charge‐carrier dynamics indirectly via structural alterations: Ag‐deficient compositions demonstrate stronger charge‐carrier localization most likely because a higher density of vacant sites in the cationic sublattice imparts enhanced lattice softness. Unraveling such delicate interplay between chemical composition, crystal structure, and charge‐carrier dynamics in (AgI)x(BiI3)y rudorffites provides crucial insights for developing a material‐by‐design approach in the quest for highly efficient Bi‐based PIMs.