Shuaifeng Hu

Abstract:

Vacuum-based deposition is a scalable, solvent-free industrial method ideal for uniform coatings on complex substrates. However, all vacuum-deposited perovskite solar cells fabricated by thermal evaporation trail solution-processed counterparts in efficiency and stability due to film quality challenges, necessitating advancement and improved understanding. Here, we report a co-evaporation route for 1.67-eV wide-bandgap perovskites by introducing a PbCl2 co-source to optimize film quality. We promote perovskite formation with pronounced (100) “face-up” orientation and deliver a certified all vacuum-deposited solar cell with 18.35% efficiency (19.3% in the lab) for 0.25-cm2 devices (18.5% for 1-cm2 cells). These cells retain 80% of peak efficiency after 1,080 hours under the ISOS-L-2 protocol. Leveraging operando hyperspectral imaging, we provide spatiotemporal spectral insight into halide segregation and trap-mediated recombination, correlating microscopic luminescence features with macroscopic device performance while distinguishing radiative from non-ideal recombination channels. We further demonstrate 27.2%-efficient 1-cm2 evaporated perovskite-on-silicon tandems and outdoor stability of all vacuum-deposited tandems in Italy, retaining ~80% initial performance after 8 months.

Abstract:

Improving the bulk quality of perovskite films is critical for achieving higher-performance photovoltaic devices. Chloride-containing additives, including lead chloride (PbCl₂) and methylammonium chloride (MACl)—standard additives widely adopted in perovskite photovoltaics—are effective for controlling crystallisation kinetics and grain morphology. However, the distinct impacts of different forms of chloride additives on nanoscale phase uniformity and luminescence homogeneity remains underexplored. Here, we provide new insights into how the choice and combination of chloride additives influence phase transitions and spatially uniform carrier dynamics within perovskite films. We demonstrate that strategically combining MACl and PbCl2 improves crystallinity and optoelectronic uniformity across dimensions spanning micrometres to millimetres. Leveraging these findings, we fabricated inverted (p-i-n) perovskite solar cells achieving certified quasi-steady-state efficiencies of 26.4% and 24.5% at device areas of 0.05 and 1 cm², respectively. Furthermore, these devices exhibit robust operational stability, retaining 88% of their initial performance after 1200 hours of continuous maximum power point tracking at elevated temperatures (65 °C) under simulated AM1.5G illumination. Our results elucidate the mechanistic differences between chloride additive forms, providing a viable strategy for advancing large-area, high-efficiency, and thermally stable perovskite photovoltaics.