Improved Efficiency of Perovskite Solar Cells Using a Nitrogen-Doped Graphene-Oxide-Treated Tin Oxide Layer

Tin oxide (SnO₂) is widely adopted as an electron transport layer in perovskite solar cells (PeSCs) because it has high electron mobility, excellent charge selective behavior owing to a large band gap of 3.76 eV, and low-temperature processibility. To achieve highly efficient SnO₂-based PeSCs, it is necessary to control the oxygen vacancies in the SnO₂ layer, since the electrical and optical properties vary depending on the oxidation state of Sn. This study demonstrates that the performance of PeSCs may be improved by using 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 used to assess their performance, including X-ray photoelectron spectroscopy, dark current analysis, and the dependence of the open-circuit voltage on light intensity. Compared with the average power conversion efficiency (PCE) of control devices, PeSCs with SnO₂:NGO composite layers exhibit greater PCEs with less deviation. Therefore, the introduction of NGO in a SnO₂ layer can be regarded as an effective method of controlling the oxidation state of SnO₂ to improve the performance of PeSCs.