Synthesis and electrochemical performance of α-Al(2)O(3) and M-Al(2)O(4) 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.