Mn doped quantum dot sensitized solar cells with power conversion efficiency exceeding 9%

Abstract

Transition metal ion (especially Mn²⁺) doping has been proven to be an effective approach to modify the intrinsic photo-electronic properties of semiconductor quantum dots (QDs). However, previous works to directly grow Mn doped QDs on TiO₂ film electrodes at room temperature resulted in the potential of the Mn dopant not being fully demonstrated in quantum dot sensitized solar cells (QDSCs). Herein, Mn doped CdSe_0.65Te_0.35 QDs (simplified as Mn : QD) were pre-synthesized via a “growth doping” strategy at high temperature. A QD-sensitized photoanode with the configuration TiO₂/Mn : QD/Mn : ZnS/SiO₂ was prepared and corresponding cell devices were constructed using Cu₂S/brass counter electrodes and polysulfide electrolyte, together with reference cells with the photoanode configurations TiO₂/Mn : QD/ZnS/SiO₂, TiO₂/QD/Mn : ZnS/SiO₂, and TiO₂/QD/ZnS/SiO₂. The photovoltaic performance results indicate that TiO₂/Mn : QD/Mn : ZnS/SiO₂ cells exhibit the best photovoltaic performance among all the studied cell devices with a power conversion efficiency (PCE) for the champion cell of 9.40% (J_sc = 20.87 mA cm⁻², V_oc = 0.688 V, FF = 0.655) under AM 1.5 G one full sun illumination, which is among the best results for QDSCs. The open circuit voltage decay (OCVD), impedance spectroscopy (IS) and transient absorption (TA) measurements confirm that the Mn²⁺ dopant can suppress charge recombination and improve the photovoltage and PCE of the resulting cells.