The dynamic CsBr treatment on α-CsPbI3 significantly improves the power conversion efficiency, reproducibility, and stability of all-inorganic CsPbI3−xBrx perovskite solar cells.

Graphene has recently attracted much interest as a material for flexible, transparent electrodes or active layers in electronic and photonic devices. However, realization of such graphene-based devices is limited due to difficulties in obtaining patterned graphene monolayers on top of materials that are degraded when exposed to a high-temperature or wet process. We demonstrate a low-temperature, dry process capable of transfer-printing a patterned graphene monolayer grown on Cu foil onto a target substrate using an elastomeric stamp. A challenge in realizing this is to obtain a high-quality graphene layer on a hydrophobic stamp made of poly(dimethylsiloxane), which is overcome by introducing two crucial modifications to the conventional wet-transfer method – the use of a support layer composed of Au and the decrease in surface tension of the liquid bath. Using this technique, patterns of a graphene monolayer were transfer-printed on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate and MoO3, both of which are easily degraded when exposed to an aqueous or aggressive patterning process. We discuss the range of application of this technique, which is currently limited by oligomer contaminants, and possible means to expand it by eliminating the contamination problem.

Compositional engineering of recently arising methylammonium (MA) lead (Pb) halide based perovskites is an essential approach for finding better perovskite compositions to resolve still remaining issues of toxic Pb, long-term instability, etc. In this work, we carried out crystallographic, morphological, optical, and photovoltaic characterization of compositional MASnPbIBr by gradually introducing bromine (Br) into parental Pb-Sn binary perovskite (MASnPbI) to elucidate its function in Sn-rich (Sn:Pb = 6:4) perovskites. We found significant advances in crystallinity and dense coverage of the perovskite films by inserting the Br into Sn-rich perovskite lattice. Furthermore, light-intensity-dependent open circuit voltage (V) measurement revealed much suppressed trap-assisted recombination for a proper Br-added (x = 0.4) device. These contributed to attaining the unprecedented power conversion efficiency of 12.1% and V of 0.78 V, which are, to the best of our knowledge, the highest performance in the Sn-rich (≥60%) perovskite solar cells reported so far. In addition, impressive enhancement of photocurrent-output stability and little hysteresis were found, which paves the way for the development of environmentally benign (Pb reduction), stable monolithic tandem cells using the developed low band gap (1.24-1.26 eV) MASnPbIBr with suggested composition (x = 0.2-0.4).

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