Photoactive Zn‐Chlorophyll Hole Transporter‐Sensitized Lead‐Free Cs₂AgBiBr₆ Perovskite Solar Cells

The lead‐free double perovskite, Cs₂AgBiBr₆, has received keen attention as photovoltaic absorber with nontoxicity and highly stabilities. However, the large bandgap (2.1 eV) and low optical absorption property of Cs₂AgBiBr₆ have limited its power conversion efficiency (PCE) in perovskite solar cells (PSCs) to low values around 2% due to the lack in short‐circuit current density (J_sc). Herein, Cs₂AgBiBr₆ perovskite is combined with a photoactive zinc chlorophyll derivative (Zn‐Chl) as a hole‐transporting layer (HTL) that is capable of sensitizing the perovskite absorber. The Zn‐Chl‐sensitized Cs₂AgBiBr₆ device exhibits a PCE up to 2.79%, the highest value for double perovskite‐based solar cells to date, with a J_sc of 3.83 mA cm⁻², which is 22–27% higher than that of the devices with conventional nonphotoactive HTLs such as 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD), poly(3‐hexylthiophene) (P3HT), and poly(triarylamine) (PTAA). Through photophysical investigation, it is found that the Zn‐Chl not only plays the role of an HTL but also the role of a photoactive layer in the PSC devices. Moreover, the Zn‐Chl‐based device shows a much higher extinction coefficient than those based on Spiro‐OMeTAD, P3HT, and PTAA. This work demonstrates promise toward the realization and application of environmentally friendly solar cells.