The aim of this study is to describe the performance of the aluminum oxide nanoparticle and metal aluminate spinel nanoparticle as photo-anodes in quantum dot photovoltaic. By using a sol-gel auto combustion method, Al2O3 NPs, CoAl2O4, CuAl2O4, NiAl2O4, and ZnAl2O4 were successfully synthesized. The formation of Al2O3 NPs and MAl2O4 (M=Co, Cu, Ni, Zn) nanocomposite was confirmed by using several characteristics such as XRD, UV-Vis, FTIR, FE-SEM, and EDX spectra. The XRD shows that the CoAl2O4 has a smaller crystallite size (12.37 nm) than CuAl2O4, NiAl2O4, and ZnAl2O4. The formation of a single-phase spinel structure of the calcined samples at 1100 °C was confirmed by FTIR. Our studies showed that the pure Al2O3 NPs have a lower energy gap (1.37 eV) than synthesized MAl2O4 under UV-Vis irradiation. Due to the well separation between the light-generated electrons and the formed holes, the cell containing ZnAl2O4 nanocomposite with CdS QDs has the highest efficiency of 8.22% and the current density of 22.86 mA cm-2, while the cell based on NiAl2O4 as a photoelectrode, six cycles of CdS/ZnS QDs, and P-rGO as a counter electrode achieved the best (PCE) power conversion efficiency of 15.14% and the current density of 28.22 mA cm-2. Electrochemical impedance spectroscopy shows that ZnAl2O4 and NiAl2O4 nanocomposites have the highest life times of the photogenerated electrons (τn) of 11*10-2 and 96*10-3 ms, respectively, and the lowest diffusion rates (Keff) of 9.09 and 10.42 ms-1, respectively.
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