Mixed-SAM interface enables efficient and stable semi-transparent perovskite solar cells for day–night ambient-light energy harvesting

Abstract

Transparent perovskite photovoltaics hold strong promise for energy-harvesting window applications. Yet in inverted (p–i–n) devices, the use of low-concentration precursor solutions to achieve high transparency renders the buried self-assembled monolayer (SAM) vulnerable to polar-solvent erosion, leading to incomplete coverage and interfacial defects. We address this limitation by co-assembling 1,2,4-benzenetricarboxylic acid (trimellitic acid, TMLA) with Me-4PACz to form a mixed SAM that can anchor via multiple carboxylate bonds, improving resistance to solvent erosion. The mixed SAM leads to better wet-film spreading, more uniform nucleation with larger grain growth, and fewer interfacial trap sites, suppressing non-radiative recombination. Semitransparent inverted devices deliver about 21% average visible transmittance with about 15% front-side efficiency (VOC about 1.15 V, FF about 76%) and negligible hysteresis. Unencapsulated cells retain over 93% of initial output after 216 h of continuous illumination and day–night cycling. Under 1000-lux LED illumination, devices reach 19.3% efficiency, highlighting indoor energy harvesting. EnergyPlus simulations of double-pane photovoltaic windows indicate reductions of about 5–24% in annual purchased electricity. By stabilizing the buried interface while preserving transparency, the mixed-SAM strategy enables reliable day–night power generation and provides a general route to ultrathin, high-quality perovskite films for green-building and low-power IoT applications.