CuInSe2 and CuInSe2–ZnS based high efficiency “green” quantum dot sensitized solar cells

Abstract

CuInSe₂ (CISe) based quantum dots (QDs), are perceived to be promising alternatives to those of cadmium or lead chalcogenide based QDs in serving as light-harvesting sensitizer materials in quantum dot sensitized solar cells (QDSCs) due to their near-infrared (NIR) absorbing capacity and low toxicity. Herein, we have synthesized high quality CISe QDs via the organic phase high temperature route, and then alloying with ZnS to form the CISe–ZnS QDs with higher chemical stability and superior optoelectronic properties. The obtained “green” CISe and CISe–ZnS QD sensitizers were immobilized onto TiO₂ film electrodes with high loading amount through the linker molecule assisted post synthesis assembly approach with the use of MPA-capped water-soluble QDs. Hindered charge recombination in the built CISe–ZnS QD based solar cells in comparison with reference CISe cells has been confirmed by impedance spectroscopy, as well as transient photovoltage decay measurements. With the combination of high QD loading and passivated trap-state defects, the resulting regenerative sandwich CISe–ZnS QD based champion solar cells exhibited an efficiency of 6.79% (J_sc = 22.61 mA cm⁻², V_oc = 0.583 V, FF = 0.515) under AM 1.5 G full one sun irradiation. The obtained efficiency was among the best performances for liquid-junction QDSCs and also demonstrated comparable photovoltaic performance of “green” CISe based QDs to the toxic cadmium and lead chalcogenide QDs.