Synthesis and electrochemical performance of α-Al2O3 and M-Al2O4 spinel nanocomposites in hybrid quantum dot-sensitized solar cells

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, Al 2 O 3 NPs, CoAl 2 O 4 , CuAl 2 O 4 , NiAl 2 O 4 , and ZnAl 2 O 4 were successfully synthesized. The formation of Al 2 O 3 NPs and MAl 2 O 4 (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 CoAl 2 O 4 has a smaller crystallite size (12.37 nm) than CuAl 2 O 4, NiAl 2 O 4 , and ZnAl 2 O 4 . 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 Al 2 O 3 NP s have a lower energy gap (1.37 eV) than synthesized MAl 2 O 4 under UV–Vis irradiation. Due to the well separation between the light-generated electrons and the formed holes, the cell containing ZnAl 2 O 4 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 NiAl 2 O 4 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 ZnAl 2 O 4 and NiAl 2 O 4 nanocomposites have the highest life times of the photogenerated electrons ( τ n ) of 11*10 −2 and 96*10 −3 ms , respectively, and the lowest diffusion rates (K eff ) of 9.09 and 10.42 ms −1 , respectively.