Synergistic Optimization of Ultrathin Perovskite Buried Interfaces via Tailored Solvent Engineering for High-Performance Semitransparent Perovskite Solar Cells

Semitransparent perovskite solar cells (ST-PSCs) typically require ultrathin perovskite films (<200 nm) to balance photovoltaic performance and optical transmittance, meeting the practical demands of building-integrated photovoltaics (BIPV). However, low-concentration precursor solutions used for fabricating such ultrathin films often result in poor film densification and exacerbate the desorption of self-assembled monolayers (SAMs), leading to instability at the buried interface. This study presents a novel low-sensitivity solvent strategy employing a strategically designed dimethylformamide (DMF)/ N -methyl-2-pyrrolidone (NMP)/chlorobenzene (CB) ternary cosolvent system to finely tune the interaction between perovskite adducts and SAMs, while suppressing excess solvent-induced disruption at the fragile SAM interface. This approach ensures uniform interfacial contact and enables the formation of ultrathin perovskite films with low defect densities. Notably, the enhanced nucleation kinetics and homogeneous grain distribution also promote preferential crystallographic orientation, which is beneficial for carrier transport. The optimized ST-PSCs achieved a champion power conversion efficiency (PCE) of 14.88% and an average visible transmittance (AVT) of nearly 21%, along with outstanding long-term storage stability (T90 = 1100 h) and operational durability under light–dark cycling (T90 = 232 h). Additionally, a thermodynamic-limit-based performance evaluation method was developed to systematically analyze performance losses in semitransparent devices. This work provides new directions for optimizing low-concentration perovskite precursor solutions and lays an important foundation for the application of ST-PSCs in BIPV.