Imporved efficiency of perovskite solar cells using a nitrogen doped graphene oxide treated tin oxide layer

Abstract

Due to high electron mobility, excellent charge selective behavior with a large band gap of 3.76 eV, and low temperature processibility, tin oxide (SnO2) is commonly used as an electron transport layer in perovskite solar cells (PeSCs). Since the electrical and optical properties vary depending on the oxidation state of Sn, it is necessary to control the oxygen vacancies in the SnO2 layer in order to reach highly efficient SnO2-based PeSCs, This study demonstrates that PeSCs based on SnO2 can be enhanced by introducing nitrogen doped graphene oxide (NGO) as an oxidizing agent for SnO2. Since NGO changes the oxidation state of the Sn in SnO2 from Sn2+ to Sn4+, the oxygen vacancies in SnO2 can be reduced using NGO. Multiple devices are fabricated and various techniques are analyzed to define their performance, including X-ray photoelectron spectroscopy, dark current analysis, and the change of the open circuit voltage depending on light intensity. PeSCs with SnO2:NGO composite layers show superior Voc with less deviation compared to the average power conversion efficiency (PCE) of control devices. Therefore, introducing NGO in a SnO2 layer can be treated as an simple method of controlling the oxidation state of SnO2 to enhance the performance of PeSCs.