Dependence of power conversion properties of perovskite solar cells on operating temperature

Power conversion properties of perovskite solar cells are studied in the temperature range of 310 K to 240 K (and recovering back). As the temperature lowers down, the fill factor (FF) decreases while the open circuit voltage (VOC) increases in the case of reverse scans (scanning from positive voltages to negative ones). The decreased FF is ascribed to the increased resistance of charge transport materials (both TiO2 and Spiro-OMeTAD) as well as the increased interfacial charge transfer resistance, while the increased VOC is due to retarded recombination which is revealed by the transient photovoltage decay measurement. Hysteresis appears in the current-voltage curves, but it shrinks with temperature decreasing and even vanishes as the temperature becomes lower than 270 K. Mott-Schottky capacitance analysis shows that ion migration exists in the device, especially for temperatures >270 K. The “S shape” current-voltage characteristic is observed at lowered temperatures, which is caused by retarded charge extraction across the interface between the active layer and charge-transport materials. Similar power conversion properties are observed when elevating the temperature from 240 K to 310 K; thus, the temperature-sensitive behavior is reversible. The observed behavior is compared with silicon solar cells. The study shows that lowering the temperature is harmful to the charge extraction processes of perovskite solar cells. Highly conductive charge-transport materials are needed for the devices to operate in a colder environment.