Interface passivation using an ammonium salt can effectively improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Despite significant PCE improvement achieved in previous studies, the selection criteria for ammonium salts are not fully understood. Here we apply a machine-learning (ML) method to investigate the relationship between the molecular features of ammonium salts and the PCE improvement of PSCs. We establish an ML model using an experimental data set of 19 salts to predict the PCE improvement after passivation. Three molecular features (hydrogen bond donor, hydrogen atom, and octane−water partition coefficient) are identified as the most important features of selecting an ammonium salt for passivation. The ML model is further used to screen ammonium salts from a pool of 112 salts in the PubChem database. FAMACs and FAMA-based PSCs fabricated with a model-recommended salt (2-phenylpropane-1aminium iodide) achieve PCEs of 22.36% and 24.47%, respectively.

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Electrochromic smart windows can reduce the energy consumption of buildings by managing the light and heat transmission. However, they need external power to work, raising the installation cost and compromising the aesthetics of the buildings. Self‐powered smart windows without external power sources have great potential in practical applications. Transparent solar cells can be integrated with smart windows and serve as their power sources. High optical transmittance, good color neutrality, and high power conversion efficiency (PCE) are required for the transparent solar cells to meet the optical and power requirements of self‐powered smart windows. Herein, an efficient MAPbCl3‐based transparent perovskite solar cell (TPSC) using a solvent‐assisted two‐step approach is developed. The transparency and color‐neutrality of the TPSCs are optimized through delicately selecting and pairing the charge transport layers and transparent electrodes. The TPSCs achieve a PCE up to 1.06% and average visible transmittance up to 72%. Self‐powered smart windows powered by the TPSCs show fast and reversible modulation of visible light from 55% to 5% without external power input. This work demonstrates the prospect of deploying TPSCs in a self‐powered smart window for energy saving and sustainable buildings.

Tremendous progress has been made in lead halide perovskite solar cells (PSCs) with the record power conversion efficiency exceeding 25%. However, poor stability is the most significant obstacle hindering their practical applications. Therefore, improving stability becomes the primary focus of PSC research. Recently, a strategy of modifying the three-dimensional perovskite structures with hydrophobic organic cations for two-dimensional (2D) perovskites has been explored and proven beneficial for both PSC efficiency and stability. Herein, multi-dimensional tuning of the bulk and interfaces of perovskite materials and their influences on device performance and stability are reviewed. In addition, the effects of defect passivation and interface functionalization are discussed. Finally, the mechanisms of stability improvement through 2D modifications are discussed.

The electron transport layer (ETL) plays an important role on the performance and stability of perovskite solar cells (PSCs). Developing double ETL is a promising strategy to take the advantages of different ETL materials and avoid their drawbacks. Here, an ultrathin SnO2 layer of ~ 5 nm deposited by atomic layer deposit (ALD) was used to construct a TiO2/SnO2 double ETL, improving the power conversion efficiency (PCE) from 18.02% to 21.13%. The ultrathin SnO2 layer enhances the electrical conductivity of the double layer ETLs and improves band alignment at the ETL/perovskite interface, promoting charge extraction and transfer. The ultrathin SnO2 layer also passivates the ETL/perovskite interface, suppressing nonradiative recombination. The double ETL achieves outstanding stability compared with PSCs with TiO2 only ETL. The PSCs with double ETL retains 85% of its initial PCE after 900 hours illumination. Our work demonstrates the prospects of using ultrathin metal oxide to construct double ETL for high-performance PSCs.