An energy level alignment strategy to boost the open-circuit voltage via a Mg:TiO2 compact layer in the planar heterojunction CsPbBr3 solar cells

Abstract

The suitable energy level alignment between the electron transport layer (ETL) and perovskite absorber for facilitating electron extraction and transfer is essential for planar heterojunction perovskite solar cells (PSCs) to achieve high power conversion efficiency (PCE). The planar heterojunction CsPbBr3 PSCs have attracted increasing attention due to their high stability in ambient in which TiO2 is often used as the ETL. Actually, there is a large energy barrier between the conduction bands of TiO2 and CsPbBr3, which limits the open-circuit voltage (VOC) and PCE of PSCs. Herein, we effectively optimized the energy level alignment between CsPbBr3 and TiO2 by tuning the Mg incorporation level in the latter. The Fermi level of TiO2 ETL was gradually shifted upward using Mg incorporation, which led to a favorable band bending between TiO2 and CsPbBr3 and reduced the interfacial band offset. Consequently, the VOC of the devices was effectively increased from 1.36 to 1.49 V, and the corresponding PCE was also increased from 6.87% to 8.76%. This work highlights the importance of the energy level alignment between ETLs and perovskite absorbers for high-performance devices and offers an effective means to address the large energy barrier between the conduction bands of TiO2 and CsPbBr3.