Improving Interfacial Charge Recombination in Planar Heterojunction Perovskite Photovoltaics with Small Molecule as Electron Transport Layer

Although perovskite solar cells (PSCs) have emerged as a promising alternative to widely used fossil fuels, the involved high-temperature preparation of metal oxides as a charge transport layer in most state-of-the-art PSCs has been becoming a big stumbling block for future low-temperature and large-scale R2R manufacturing process. Such an issue strongly encourages scientists to find new type of materials to replace metal oxides. Except for expensive PC61BM with unmanageable morphology and electrical properties, the past investigation on the development of low-temperature-processed and highly efficient electron transport layers (ETLs) has met some mixed success. In order to further enhance the performance of all-solution-processed PSCs, we propose a novel n-type sulfur-containing small molecule hexaazatrinaphtho[2,3-c][1,2,5] thiadiazole (HATNT) with high electron mobility up to 1.73 x 10(-2) cm(2) V-1 s(-1) as an ETL in planar heterojunction PSCs. A high power conversion efficiency of 18.1% is achieved, which is fully comparable with the efficiency from the control device fabricated with PC61BM as ETL. This superior performance mainly attributes from more effective suppression of charge recombination at the perovskite/HATNT interface than that between the perovskite and PC61 BM. Moreover, high electron mobility and strong interfacial interaction via S-I or S-Pb bonding should be also positive factors. Significantly, our results undoubtedly enable new guidelines in exploring n-type organic small molecules for high-performance PSCs.