Vertical Interaction between Thiourea and Perovskite Surface Results in Obviously Enhanced Performance with PCE Surpassing 24% Efficiency

Thiourea has been employed for the modification of perovskite (PVK) films and demonstrates favorable modification effects. However, few studies have addressed the binding mode of thiourea (Th) with perovskite crystal facets. In this work, DFT calculations reveal that thiourea exhibits a perpendicular binding orientation to the (100) facet of perovskite, enabling the lone pair electrons of the S atom in the C═S bond to interact with undercoordinated Pb atoms. Meanwhile, due to charge transfer, the −NH2 group and the S atom form bonds with positively charged sites in perovskite. PL, TRPL, SCLC, and KPFM results indicate a significant reduction of defects in the PVK. Eventually, the Th-perovskite device yielded a notable improvement in performance: open-circuit voltage (VOC) increased from 1.12 to 1.16 V, short-circuit current density (JSC) rose from 24.48 to 25.13 mA/cm2, the fill factor (FF) reached 82.35%, and the power conversion efficiency (PCE) was enhanced from 21.90% to 24.01%. Importantly, the devices retained 80% of their initial efficiency after operating for 15 days under 50% relative humidity, demonstrating significant progress in moisture tolerance for practical applications. This work highlights that vertical binding of small organic molecules to the perovskite facet surface can more effectively enhance the performance of photovoltaics.