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.