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Metal halide perovskite solar cells (PSCs) are infamous for their batch-to-batch and lab-to-lab irreproducibility in terms of stability and performance. Reproducible fabrication of PSCs is a critical requirement for market viability and practical commercialization. PSC irreproducibility plagues all levels of the community; from institutional research laboratories, start-up companies, to large established corporations. In this work, the critical function of atmospheric humidity to regulate the crystallization and stabilization of formamidinium lead triiodide (FAPbI3) perovskites is unraveled. It is demonstrated that the humidity content during processing induces profound variations in perovskite stoichiometry, thermodynamic stability, and optoelectronic quality. Almost counterintuitively, it is shown that the presence of humidity is perhaps indispensable to reproduce phase-stable and efficient FAPbI3-based PSCs.

Advances in renewable and sustainable energy technologies critically depend on our ability to design and realize materials with optimal properties. Materials discovery and design efforts ideally involve close coupling between materials prediction, synthesis and characterization. The increased use of computational tools, the generation of materials databases, and advances in experimental methods have substantially accelerated these activities. It is therefore an opportune time to consider future prospects for materials by design approaches. The purpose of this Roadmap is to present an overview of the current state of computational materials prediction, synthesis and characterization approaches, materials design needs for various technologies, and future challenges and opportunities that must be addressed. The various perspectives cover topics on computational techniques, validation, materials databases, materials informatics, high-throughput combinatorial methods, advanced characterization approaches, and materials design issues in thermoelectrics, photovoltaics, solid state lighting, catalysts, batteries, metal alloys, complex oxides and transparent conducting materials. It is our hope that this Roadmap will guide researchers and funding agencies in identifying new prospects for materials design.

In our paper, we reported a previously unobserved Raman-like band centered at around 550 cm-1 [e.g., Figs. 2(a) and 3(a)] and found that it diminished after the material degraded. Our latest study has revealed that the assignment of the 550 cm-1 band as a Raman band was erroneous, and this Raman-like peak was in fact the result of stray light of the unusually strong photoluminescence (PL) signal, peaked at around 770 nm, in the pristine sample. The strongest band-edge PL intensity was on the order of (0.5-1.0) × 105 cps [e.g., Figs. 2(b) and 3(d)] at the same or comparable power as the Raman measurements. Assuming a typical stray-light suppression ratio of 10-4 to 10-5 for a single grating spectrometer (an exact value is not available from the manufacturer of the instrument), the stray-light level would be comparable to that of the observed "Raman" peak typically on the order of 1 cps. In our new study, this broad band was eliminated after adding an appropriate short-pass filter to block the band-edge PL signal. The broad band at around 1340 cm-1, as shown in Fig. 5(a), has the same origin as the 550 cm-1 band. The observed anticorrelation between the signals of around 100 cm-1 and 550 cm-1 was the result of structure degradation that enhanced the Raman signal near 100 cm-1 and, in the meantime, reduced the PL signal near the perovskite bandgap at around 770 nm but appeared at 550 cm-1 as stray light. The wrong interpretation of 550 cm-1 does not affect the primary conclusion, i.e., the multiple-stage structure transformation and the interpretation of other results.We regret this error and intend to write a paper to report the latest findings in detail in the near future. The effort of Jose F. Castaneda, a new Ph.D. student in Zhang's group, has led to the finding of this error.

In this study, eutectic gallium–indium alloy (EGaIn) liquid metal is used as the rear electrode for perovskite solar cells (PSCs), where the interfacial properties of the device, particularly the beneficial roles of the surface oxide of the liquid metal, are explored. The findings demonstrate that the native oxide of the EGaIn electrode significantly affects the stability of photovoltaic performance and impedance characteristics including series and shunt resistances. Based on the results, the following hypothesis is formulated: the oxide interlayer serves two crucial functions of a barrier against metal diffusion and a tunnel for enhancing charge extraction and transfer. The results of elemental mapping and trap density calculation support the former function of the hypothesis that the oxide film can effectively prevent metal penetration into the perovskite layer. Furthermore, measurements involving capacitance−voltage and time‐resolved photoluminescence confirm that the oxide film on the liquid metal eliminates the interfacial Schottky barrier, promoting efficient charge extraction and transfer processes. Finally, the investigation is extended to develop flexible PSCs using the EGaIn electrode, which consistently exhibits stable performance during repeated bending cycles. Notably, the EGaIn rear electrode can be readily removed and collected through a straightforward acid treatment, offering a promising avenue for efficient cell recycling. [ABSTRACT FROM AUTHOR]

Halide perovskite single crystals (SCs) have attracted much attention for their application in high‐performance x‐ray detectors owing to their desirable properties, including low defect density, high mobility–lifetime product (μτ), and long carrier diffusion length. However, suppressing the inherent defects in perovskites and overcoming the ion migration primarily caused by these defects remains a challenge. This study proposes a facile process for dipping Cs0.05FA0.9MA0.05PbI3 SCs synthesized by a solution‐based inverse temperature crystallization method into a 2‐phenylethylammonium iodide (PEAI) solution to reduce the number of defects, inhibit ion migration, and increase x‐ray sensitivity. Compared to conventional spin coating, this simple dipping process forms a two‐dimensional PEA2PbI4 layer on all SC surfaces without further treatment, effectively passivating all surfaces of the inherently defective SCs and minimizing ion migration. As a result, the PEAI‐treated perovskite SC‐based x‐ray detector achieves a record x‐ray sensitivity of 1.3 × 105 μC Gyair−1 cm−2 with a bias voltage of 30 V at realistic clinical dose rates of 1–5 mGy s−1 (peak potential of 110 kVp), which is 6 times more sensitive than an untreated SC‐based detector and 3 orders of magnitude more sensitive than a commercial α‐Se‐based detector. Furthermore, the PEAI‐treated‐perovskite SC‐based x‐ray detector exhibits a low detection limit (73 nGy s−1), improved x‐ray response, and clear x‐ray images by a scanning method, highlighting the effectiveness of the PEAI dipping approach for fabricating next‐generation x‐ray detectors. [ABSTRACT FROM AUTHOR]