No abstract

CF3PEAI, an amphipathic passivation agent, can passivate multiple perovskite defects leading to high performance and stability of perovskite solar cells.

Metal-halide perovskite-based green and red light-emitting diodes (LEDs) have witnessed a rapid development because of their facile synthesis and processability; however, the blue-band emission is constrained by their unstable chemical properties and poorly conducting emitting layers. Here, we show a trioctylphosphine oxide (TOPO)-mediated one-step approach to realize bright deep-blue luminescent FAPbBr3 nanoplatelets (NPLs) with enhanced stability and charge transport. The concentration of NPL surface ligands is shown to be progressively tuned via varying the amount of intermediate TOPO due to the acid–base equilibrium between protic acid and TOPO. By effectively optimizing the concentration of surface ligands, the structural integrity of NPL solids can be preserved in ambient air for a week, mainly because of the highly ordered and dense solid assembly and the reduced defects. The removal of excess organic ligands also enables the improvement of charge mobility by orders of magnitude. Ultimately, ultrapure deep-blue perovskite LEDs (439 nm) with a narrow emission width of 14 nm and a peak EQE of 0.14% are achieved at low driving voltage. Our finding expands the current understanding of surface ligand modulation in the development of pure bromide deep-blue perovskite optoelectronics.

Perovskite solar cells (PSCs) are considered one of the most promising nextgeneration examples of high-tech photovoltaic energy converters, as they possess an unprecedented power conversion efficiency with low cost. A typical high-performance PSC generally contains a perovskite active layer sandwiched between an electron-transport layer (ETL) and a hole-transport layer (HTL). The ETL and HTL contribute to the charge extraction in the PSC. However, these additional two layers complicate the manufacturing process and raise the cost. To extend this technology for commercialization, it is highly desired that the structure of PSCs is further simplified without sacrificing their photovoltaic performances. Thus, ETL-free or/and HTL-free PSCs are developed and attract more and more interest. Herein, the commonly used methods in reducing the defect density and optimizing the energy levels in conventional PSCs in order to simplify their structures are summarized. Then, the development of diverse ETL-free or/and HTL-free PSCs is discussed, with the PSCs classified, including their working principles, implemented technologies, remaining challenges, and future perspectives. The aim is to redirect the way toward low-cost and high-performance PSCs with the simplest possible architecture.

Metal halide perovskites witness a huge development in light‐emitting diodes (LEDs) triggered by their unique optical and optoelectronic properties. However, blue emission perovskite LEDs lag behind their red and green counterparts in efficiency, due to the difficulties in synthesizing stable materials and maintaining quantum efficiency in thin films as high as in solution. The nanoplatelets (NPLs), with exciton binding energies up to several hundreds of meV, exhibit fundamentally different excitonic behavior from 0D nanocrystals. Meanwhile the bandgap tunability with thickness makes them promising for blue optoelectronic devices. Here, a brief review on recent progress in perovskite light emission, and the opportunities and challenges in pure bromide‐based perovskite NPLs for the blue‐emitting regime are provided. In particular, the important roles of surface ligands and emitting layer quality on devices are highlighted. The trade‐off between well surface passivation and efficient charge transportation is analyzed. Furthermore, it is recommended that more efforts should be put on exploring the carrier dynamics in NPLs, which act as guidelines for optimization of materials and improvement of devices.