Low-Temperature Melting-Crystallization Transition in Perovskites With Self-Trapped Excitons for Photovoltaic Downconversion.

Self-trapped exciton (STE) emitters demonstrate exceptional luminescent downconversion (LDC) performance, achieving near-unity photoluminescence quantum yields (PLQY) and broadband emission that overcomes Stokes shift limitations in conventional fluorophores. While these properties originate from precisely engineered Jahn-Teller distorted centers through optimized ligand fields and quantum confinement, practical challenges in stability and solution processability have hindered photovoltaic integration. In this work, we develop tin-halide perovskite exhibiting unique low-temperature (125°C) reversible melting-crystallization transitions for solution processability, as well as highly efficient (>90% PLQY) broadband LDC through zero-dimensional STE emission. When integrated as the LDC layer, this reversible melting-crystallization STE emitter enhances the external quantum efficiency of silicon solar cells in the short-wavelength region, leading to an absolute improvement in power conversion efficiency of over 0.75%. Our findings establish a new paradigm for low-temperature melt-processed perovskite integration in silicon photovoltaics, offering both economic viability and scalability for performance enhancement beyond current technological limits.