Simple benzothiadiazole derivatives as buried interface materials towards efficient and stable n–i–p perovskite solar cells

Abstract

The state-of-the-art electron transport materials (ETMs) in n–i–p perovskite solar cells (PSCs) strongly rely on inorganic metal oxides (e.g. TiO₂), but they often require high-temperature fabrication and complicated manufacturing. Moreover, little attention has been paid to understanding the influences of the ETM surface nature on the upper perovskite microstructures. Here, we developed a series of organic benzothiadiazole (BT) derivatives as ETMs with simple synthesis and facile fabrication. Fine modulation of the pendant groups in BT-based ETMs enables effective optimization of the upper perovskite layer in terms of crystallinity, microstructures, morphology, and conductivity. F-substituted BTF–BA as a buried interface material produces a perovskite thin film with high uniformity, enhanced conductivity, suppressed nonradiative recombination and remarkable film stability, all of which are superior to conventional TiO₂ and PCBM. Significantly, the resulting devices with BTF–BA yield a remarkable power conversion efficiency (PCE) of 19.6%, representing the record efficiency for organic non-fullerene ETMs in n–i–p devices, which is an over 10% efficiency enhancement compared to conventional TiO₂ (17.8%) and PCBM (16.3%). Furthermore, the hydrophobic nature of F-substituted BTF–BA mitigates the water induced degradation mechanism and simultaneously improves the environmental stability of PSCs. The unencapsulated PSCs with BTF–BA exhibit promising stability by retaining over 90% of their initial performance after 1500 hours in air with 30% humidity. This work provides a deep understanding of buried ETM interfaces and offers an effective strategy of molecular engineering to optimize the device performance.