Chlorine‐modified SnO 2 electron transport layer for high‐efficiency perovskite solar cells

A high‐quality electron transport layer (ETL) is a critical component for the realization of high‐efficiency perovskite solar cells. We developed a controllable direct‐contact reaction process to prepare a chlorinated SnO 2 (SnO 2 ‐Cl) ETL. It is unique in that (a) 1′2‐dichlorobenzene is used to provide more reactive Cl radicals for more in‐depth passivation; (b) it does not introduce any impurities other than chlorine. It is found that the chlorine modification significantly improves the electron extraction. Consequently, its associated solar cell efficiency is increased from 17.01% to 17.81% comparing to the pristine SnO 2 ETL without the modification. The hysteresis index is significantly reduced to 0.017 for the SnO 2 ‐Cl ETL.