E-beam evaporated Nb2O5 as an effective electron transport layer for large flexible perovskite solar cells

E-beam evaporated Nb2O5 film is directly used as an effective electron transport layer (ETL) for perovskite solar cells without needing any posttreatment. The effect of Nb2O5 thickness on optical and electronic properties of the perovskite layer deposited thereupon are studied in detail. It is found that 60 nm thick Nb2O5 ETL delivers the best photovoltaic performance with PCE as high as 18.59%. In particular, e-beam evaporated Nb2O5 is found to be advantageous in large area flexible perovskite solar cells, with larger area cells showing comparable Jsc and Voc values as smaller area devices, and the PCE loss is mainly caused by increased series resistance leading to reduced FF. With proper cell design to limit the resistance and associated FF loss, it is expected that the large area cells should present respectable FF and PCEs as their smaller area devices.