Chlorophyll Derivative-Sensitized TiO₂ Electron Transport Layer for Record Efficiency of Cs₂AgBiBr₆ Double Perovskite Solar Cells

The power conversion efficiency (PCE) of Cs₂AgBiBr₆-based perovskite solar cells (PSCs) is still low owing to the inherent defects of Cs₂AgBiBr₆ films. Herein, we demonstrate a carboxy-chlorophyll derivative (C-Chl)-sensitized mesoporous TiO₂ (m-TiO₂) film as an electron transport layer (ETL) to enhance and extend the absorption spectrum of Cs₂AgBiBr₆-based PSCs. The C-Chl-based device achieves a significantly improved PCE, exceeding 3% for the first time, with an increase of 27% in short-circuit current density. Optoelectronic investigations confirm that the introduction of C-Chl reduces the defects, accelerates the electron extraction, and suppresses charge recombination at the interface of ETL/perovskite. Moreover, the unencapsulated PSCs display restrained hysteresis and great stability under ambient conditions.