Significantly enhanced energy conversion efficiency of CuInS2 quantum dot sensitized solar cells by controlling surface defects

Aiming at improving the cell performance of colloidal CuInS 2 (CIS) quantum dot sensitized solar cells (QDSCs), a modified synthetic method has been developed to prepare CIS quantum dots (QDs), and Cu/In non-stoichiometric ratios of CIS QDs have been carefully controlled for the first time. It is found that, with the amount of In element increasing, the short-circuit photocurrent density ( J sc ), open-circuit voltage ( V oc ) and fill factor ( FF ) of CIS QDSCs will gradually increase, leading to the cell performance enhanced. Up to 8.54% PCE has been achieved when the Cu/In precursor molar ratio is 1/4, which is a new record for the CIS-based solar cells. Electrochemical impedance analysis, open-circuit voltage-decay (OCVD) and time-resolved photoluminescence analyses further confirm that In-rich CIS QDs can bring about surface defect states significantly reduced, thus leading to the charge recombination at TiO 2 /CIS/electrolyte interfaces efficiently inhibited. Interfacial electron recombination mechanism of the solar cells is proposed that photo-generated carrier recombination in the cell is mainly dominated by the electron transfer process from the conduction band of TiO 2 to unoccupied defect states of CIS, which has a great influence on the FF of the device. This work provides a new and simple way to reduce the loss of photo-generated carriers, improve the interfacial carrier collection and achieve highly efficient QDSCs.