ZiQi Sun

In article number 1700264, Sven Hüttner, Pablo Docampo, and co-workers give an overview of hybrid metal halide perovskites for solar cell applications. The focus is on the series of challenges that have been overcome and those still remaining to be solved. In particular, the authors lay out their understanding of the perovskite crystallization process and how this knowledge can be harnessed to enable better performing devices; how to overcome reproducibility and hysteresis issues; and the long-term prospects of the technology in terms of stability and sustainability. Image by Criss Hohmann (Nanosystems Initiative Munich).

Recently, due to the possibility of thinning down to the atomic thickness to achieve exotic properties, layered materials have attracted extensive research attention. In particular, PbI₂, a kind of layered material, and its perovskite derivatives, CH₃NH₃PbI₃ (i.e., MAPbI₃), have demonstrated impressive photoresponsivities for efficient photodetection. Herein, the synthesis of large-scale, high-density, and freestanding PbI₂ nanosheets is demonstrated by manipulating the microenvironment during physical vapor deposition. In contrast to conventional two-dimensional (2D) growth along the substrate surface, the essence here is the effective nucleation of microplanes with different angles relative to the in-plane direction of underlying rough-surfaced substrates. When configured into photodetectors, the fabricated device exhibits a photoresponsivity of 410 mA W⁻¹, a detectivity of 3.1 × 10¹¹ Jones, and a fast response with the rise and decay time constants of 86 and 150 ms, respectively, under a wavelength of 405 nm. These PbI₂ nanosheets can also be completely converted into MAPbI₃ materials via chemical vapor deposition with an improved photoresponsivity up to 40 A W⁻¹. All these performance parameters are comparable to those of state-of-the-art layered-material-based photodetectors, revealing the technological potency of these freestanding nanosheets for next-generation high-performance optoelectronics.

High-density, crystalline, and freestanding PbI₂ and MAPbI₃ nanosheets are synthesized on a large-scale through the nucleation of microplanes on rough-surfaced substrates by manipulating the microenvironment during physical vapor deposition. When configured into photodetectors, they exhibit efficient photodetection with excellent performance in responsivity, detectivity, etc.

An alloy-free 2D monolayer WSe₂-MoS₂ lateral p-n heterojunction solar cell is demonstrated to exhibit an extraordinary power conversion efficiency of 2.56%, with excellent omnidirectional light harvesting behavior, by Lih-Juann Chen, Jr-Hau He and co-workers in article number 1701168. Temperature-dependent characteristics are analyzed and the electrode spacing is optimized to achieve gate-tuning controllability and environmentindependent cell properties.