Surface modification of halide perovskite using EDTA-complexed SnO2 as electron transport layer in high performance solar cells

Abstract

The long-term performance of metal halide perovskite solar cells (PSCs) can be significantly improved by tuning the surface characteristics of the perovskite layers. Herein, low-temperature-processed ethylenediaminetetraacetic acid (EDTA)-complexed SnO₂ (E-SnO₂) is successfully employed as an electron transport layer (ETL) in PSCs, enhancing the efficiency and stability of the devices. The effects of EDTA treatment on SnO₂ are investigated for different concentrations: comparing the solar cells' response with 15%–2.5% SnO₂ and E-SnO₂ based ETLs, and it was found that 7.5% E-SnO₂ provided the best results. The improved surface properties of the perovskite layer on E-SnO₂ are attributed to the presence of small amount of PbI₂ which contributes to passivate the defects at the grain boundaries and films' surface. However, for the excess PbI₂ based devices, photocurrent dropped, which could be attributed to the generation of shallow traps due to excess PbI₂. The better alignment between the Fermi level of E-SnO₂ and the conduction band of perovskite is another favorable aspect that enables increased open-circuit potential (V_OC), from 0.82 V to 1.015 V, yielding a stabilized power conversion efficiency of 15.51%. This complex ETL strategy presented here demonstrates the enormous potential of E-SnO₂ as selective contact to enhance the perovskite layer properties and thereby allow stable and high-efficiency PSCs.