Improving the photovoltaic performance of CdSe0.2S0.8 alloyed quantum dot sensitized solar cells using CdMnSe outer quantum dot

Abstract

In this paper, by introducing the Mn-doped CdSe (CdMnSe) layer as outer quantum dot (QD) on ternary CdSe0.2S0.8 QDs surface, we developed an effective way to enhance the power conversion efficiency (PCE) of the CdSexS1-x alloyed quantum dot sensitized solar cells (QDSSCs) when the molar ratio of Se/Na2S·9H2O is 1:4. As a result, a cascade band structure and the midgap states which favorable for electron injection and the hole transport, are obtained when the concentration of Cd2+, Se2+ and Mn2+ ions are 0.5, 0.5 and 0.05 M, respectively, in the CdMnSe outer QD deposited by the successive ionic layer absorption and reaction (SILAR) method with three cycles. Hence, with using polysulfide electrolyte and Cu2S-brass as counter electrode, the measured PCE for the CdSe0.2S0.8/10%CdMnSe QDSSC is 5.420% (Voc = 0.70 V, Jsc = 16.834 mA.cm−2, and FF = 0.460) at AM 1.5G, which is higher than the PCE of 4.327% for the device with bare CdSe0.2S0.8 QDs or a ~25.5% increase. Our findings indicate that such improvement in PCE is caused by the increasing of light-absorption, decrease of the surface roughness, improvement of electrons transfer from QDs to TiO2 CB, reduction of electrons recombination and thereby, the increasing collection of electrons in TiO2 film.