Efficient Perovskite Solar Cells over a Broad Temperature Window: The Role of the Charge Carrier Extraction

The mechanism behind the temperature dependence of the device performance in hybrid perovskite solar cells (HPSCs) is investigated systematically. The power conversion efficiency (PCE) of the reference cell using [60] PCBM as electron extraction layer (EEL) drops significantly from 11.9% at 295 K to 7% at 180 K. The deteriorated charge carrier extraction is found as the dominant factor causing this degradation. Temperature dependent spectroscopy and charge transport studies demonstrate that the poor electron transport in the [60] PCBM EEL at low temperature leads to inefficient charge carrier extraction. It is further demonstrated that the n-type doping of [60] PCBM EEL or the use of an EEL (fulleropyrrolidine with a triethylene glycol monoethyl ether side chain) with higher electron transport capability is an effective strategy to achieve HPSCs working efficiently over a broad temperature range. The devices fabricated with these highly performing EELs have PCEs at 180 K of 16.7% and 18.2%, respectively. These results support the idea that the temperature dependence of the electron transport in the EELs limits the device performance in HPSCs, especially at lower temperatures and they also give directions toward further improvement of the PCE of HPSCs at realistic operating temperatures.