[en] Highlights: • A simple solution process was exploited to obtain perovskite nanostructure assembly. • The perovskite solar cell with nanostructure assembly yields a PCE of 19.16%. • The adoption of perovskite nanostructure assembly leads to photon management. • The photon management is due to the localized gratings and fluorescence effect. • The presentation of fluorescence resonance energy transfer in perovskite solar cell. Organic-inorganic perovskite solar cells have been highlighted as one of the most competitive thin film photovoltaics recently. It is promising to further raise the power conversion efficiency if high quality absorber is coupled with rational optical design for effective photon management. Here we demonstrate the implementation of perovskite nanostructure assembly by simple solution process to interfere the propagation of light inside the adjacent absorber. It enhances light harvesting to obtain higher attainable photocurrents and photovoltage in the resultant devices, achieving a decent power conversion efficiency (PCE) over 19% consequently. The presented nanostructure assembly integrates perovskite materials with desirable processibility and chemical compatibility by chemical synthesis and interface modification. For the first time, a synergetic localized “gratings” and enhanced fluorescence effect was demonstrated to govern photon management in perovskite solar cells. These findings may serve as a general guide to design and construct perovskite thin solar cells with efficiency approaching Shockley-Queisser limit.

[en] It is widely believed that excess/residual lead iodide (PbI${}_2$) can affect the performance of perovskite solar cells . Moderate PbI${}_2$ can enhance efficiency by passivating defects, while extremely active PbI${}_2$ leads to non-negligible hysteresis effects and reduces device stability. Although several efforts are made to investigate the role of excess PbI${}_2$, its impact is still underestimated. Recent advances further demonstrate the extraordinary potential of modifying excess PbI${}_2$; however, a comprehensive study is required to obtain a deeper understanding. Herein, the important breakthroughs regarding excess PbI${}_2$ are reviewed and the mechanism of excess PbI${}_2$ in terms of efficiency and stability is rethought. In addition, the origins, verification, and regulation of residual PbI${}_2$ are summarized. (© 2023 Wiley‐VCH GmbH)

[en] Highlights: • We developed a strategy based on phase transition induced (PTI) crystal rearrangement. • Uniform grain size, low surface potential barrier and self-passivation in PTI-films. • This strategy enables fabrication of inorganic CsPbBr₃ perovskite solar cells. • Such perovskite solar cells show a high PCE of 10.91% and long-term stability -- Abstract: High efficiency and long-term stability are vital for further development of perovskite solar cells (PSCs). PSCs based on cesium lead halide perovskites exhibit better stability but lower power conversion efficiencies (PCEs), compared with organic-inorganic hybrid perovskites. Lower PCE is likely associated with trap defects, overgrowth of partial crystals and irreversible phase transition in the films. Here we introduce a strategy to fabricate high-efficiency CsPbBr₃-based PSCs by controlling the ratio of CsBr and PbBr₂ to form the perovskite derivative phases (CsPb₂Br₅/Cs₄PbBr₆) via a vapor growth method. Following post-annealing, the perovskite derivative phases as nucleation sites transform to the pure CsPbBr₃ phase accompanied by crystal rearrangements and retard rapid recrystallization of perovskite grains. This growth procedure induced by phase transition not only makes the grain size of perovskite films more uniform, but also lowers the surface potential barrier that existsbetween the crystals and grain boundaries. Owing to the improved film quality, a PCE of 10.91% was achieved for n-i-p structured PSCs with silver electrodes, and a PCE of 9.86% for hole-transport-layer-free devices with carbon electrodes. Moreover, the carbon electrode-based devices exhibited excellent long-term stability and retained 80% of the initial efficiency in ambient air for more than 2000 h without any encapsulation.