Free carrier generation and recombination in PbS quantum dot solar cells

Time Delayed Collection Field and Bias Assisted Charge Extraction (BACE) experiments are used to investigate the charge carrier dynamics in PbS colloidal quantum dot solar cells. We find that the free charge carrier creation is slightly field dependent, thus providing an upper limit to the fill factor. The BACE measurements reveal a rather high effective mobility of 2×10−3 cm2/Vs, meaning that charge extraction is efficient. On the other hand, a rather high steady state non-geminate recombination coefficient of 3×10−10 cm3/s is measured. We, therefore, propose a rapid free charge recombination to constitute the main origin for the limited efficiency of the PbS colloidal quantum dots cells.