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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:

Metal-halide perovskites are emerging as promising semiconductors for next-generation (opto)electronics. Due to their excellent optoelectronic and physical properties, as well as their processing capabilities, the past decades have seen significant progress and success in various device applications, such as solar cells, photodetectors, light-emitting diodes, and transistors. Despite their performance now rivaling or surpassing that of silicon counterparts, halide-perovskite semiconductors still face challenges for commercialization, particularly in terms of toxicity, stability, reliability, reproducibility, and lifetime. In this Roadmap, we present comprehensive discussions and perspectives from leading experts in the perovskite research community, covering various perovskite (opto)electronics, fundamental material properties and fabrication methods, photophysical characterizations, computing science, device physics, and the current challenges in each field. We hope this article provides a valuable resource for researchers and fosters the development of halide perovskites from basic to applied science.

Abstract:

Substantial VOC loss and halide segregation in wide-bandgap (WBG) perovskite sub-cells pose significant challenges for advancing all-perovskite tandem solar cells (APTSCs). Regarding this, one of the most impactful developments is the application of hole-selective self-assembled monolayers (SAMs), leading to the advancement in APTSC technology. However, SAMs with poor polar-solvent resistance would be inevitably delaminated from substrates during perovskite precursor coating, remaining great challenge in achieving a complete SAMs coverage with derivatization issues, e.g. defective perovskite and considerable interface energy loss. Here, we introduced an in-situ molecular compensation strategy to address the inherent flaw of SAMs within WBG perovskites via incorporating 5-ammonium valeric acid iodide (5-AVAI). The larger-dipole 5-AVAI spontaneously accumulates toward the buried interface to compensate the SAMs-deficient sites when depositing WBG perovskite, effectively minimizing interfacial energy loss. Simultaneously, amphoteric 5-AVAI with amino and carboxyl groups can compensate the defects at grain boundaries for solid passivation. Consequently, a champion efficiency of 20.23% with a record VOC of 1.376 V was realized on WBG devices, enabling an efficiency of 28.9% for the APTSCs. Encouragingly, the tandems showed good operational stability and retained 87.3% of their efficiency after 800 hours of tracking.

Abstract:

Halide perovskite solar cells are approaching commercialization, with solution processing emerging as a key method for large‐scale production. This study introduces a significant advancement: using non‐toxic solvents like water and alcohol in perovskite precursor inks facilitated by the protic ionic liquid methylammonium propionate (MAP). MAP effectively dissolves perovskite precursors such as lead acetate and methylammonium iodide, enabling the first stable water‐based perovskite precursor ink suitable for one‐step slot‐die coating. This new ink formulation contrasts with conventional dimethylformamide (DMF) and dimethylsulfoxide (DMSO)‐based inks, as evidenced by in‐situ grazing incidence wide‐angle X‐ray scattering (GIWAXS), which revealed an intermediate‐free liquid‐to‐solid transition. In‐situ mass spectrometry also showed that organic molecules evaporate during annealing, resulting in a crystalline perovskite phase. Optimization of the solvent mixture to H2O/IPA/MAP enabled successful slot‐die coating, yielding perovskite solar cells with an efficiency of up to 10%. This eco‐friendly ink reduces toxicity and environmental impact compared to DMF‐based inks, offering a longer shelf life and the possibility of using the ink in ambient conditions. This pioneering work represents the first report of a water‐based green ink formulation for one‐step thin film coating at room‐temperature conditions by slot‐die coating, highlighting its potential for sustainable commercial applications.

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.