Performance enhancement of mesoscopic perovskite solar cells with GQDs-doped TiO2 electron transport layer

Abstract

Electron transport layer (ETL) of perovskite solar cells (PSCs) plays an important role on transferring electrons from perovskite layer to transparent conductive oxide layer, strongly affecting PSC performance. In the present study, effects of adding graphene quantum dots (GQDs) as a dopant to the mesoscopic TiO2 (mp-TiO2) ETL on performance of a PSC were investigated. Different amounts (1.25, 2.5 and 5 vol%) of GQDs were directly added to the TiO2 precursor solution which was subsequently applied as the doped ETL by spin coating. The results showed that Jsc, Voc and FF of the 2.5 vol% GQDs-doped cell were 21.92 mA/cm2, 0.97 V and 0.63, respectively, corresponding to a PCE of 14.36% (champion cell), approximately 50% improvement compared to the un-doped cells (best PCE 9.55%). The perovskite film in the GQDs-doped cell was dense with fewer pinholes which facilitated electron extraction, and accelerated charge mobility in TiO2 layer, consequently promoting Jsc and Voc. Based on EIS results, GQDs doping into the TiO2 ETL significantly suppressed the recombination processes, resulting in a higher FF. Interestingly, the PSC based on 2.5 vol% GQDs-doped TiO2 ETL maintained ~88% of its initial PCE (champion cell), after 500 h under ambient conditions; whereas, the conventional PSC based on pure TiO2 ETL maintained only 61% of its initial PCE under the same conditions, suggesting a dramatic improvement in the device stability. The findings clearly showed that GQDs doping to TiO2 ETL could be a potential and confident approach for improving performance and stability of the mesoscopic PSCs.