AgInS2/CdSe type-II core/shell quantum dot-sensitized solar cells with an efficiency of 11.75% under 0.1 sun

We report the fabrication and photovoltaic performance of new type-II AgInS2/CdSe core/shell quantum dot-sensitized solar cells (QDSSCs). AgInS2 core and CdSe shell QDs are grown using the successive ionic layer adsorption and reaction (SILAR) method. X-ray diffraction reveals the orthorhombic and cubic structures for AgInS2 and CdSe, respectively. Optical spectra reveal the bandgaps of 1.91, 1.78, and 1.57 eV for AgInS2, CdSe, and AgInS2/CdSe, respectively. Cyclic voltammetry measurements show a type-II band alignment for the AgInS2/CdSe QDs. Liquid-junction AgInS2/CdSe QDSSCs are fabricated using a polysulfide electrolyte. Single-layered AgInS2 and CdSe QDSSCs are prepared simultaneously for comparison. The AgInS2/CdSe cell yields a PCE of 8.39% (Voc = 0.64 V, FF = 56.0%) under 1 sun, significantly higher than the single-layered AgInS2 (3.04%) and CdSe (3.67%) QDSSCs. Moreover, the Jsc increases from 7.72 in single-layered AgInS2 to 23.28 mA cm−2 in core/shell AgInS2/CdSe. The PCE of AgInS2/CdSe further increases to 11.75% under 0.1 sun. The PCE of 8.39% is comparable to the best PCE (8.26%) of Dy-doped CdTe/CdS for all type-II core/shell QDSSCs reported. The improved performance of the core/shell QDSSCs is attributed to the spatial separation of electron/hole, cascade energy structure, broader absorption band, and a possible indirect interfacial transition.