Enhanced photovoltaic efficiency in TiO2-based CdS quantum dot-sensitized solar cells by the introduction of ZnO:Al3+ nanoparticles

•A technique to fabricate quantum dots-sensitized solar cells (QDSSCs) based on TiO2 and ZnO nanoparticles is reported.•ZnO was doped with Al3+ to enhance the PCE by promoting electron mobility to form an efficient photoelectrode added to TiO2.•A maximum PCE of 3.4% was achieved with five layers of ZnO nanocubes with a 0.0005M Al3+ doping concentration.•Changes in current densities by internal resistances (Rs, Rrec and Rsh) were analyzed by fitting the diode equation.•A study of the beta factor (type of recombination) and tao (life time) are presented. A technique to fabricate quantum dots-sensitized solar cells (QDSSCs) based on Titanium Oxide (TiO2) and Zinc Oxide (ZnO) nanoparticles (NPs) is reported. ZnO nanocubes of around 65 nm were synthesized by the sol–gel precipitation method. ZnO was doped with Al3+ to enhance the photovoltaic efficiency by promoting electron mobility to form an efficient photoelectrode added to TiO2. Current density–voltage (J-V) characterizations indicate that the addition of Al3+ doping in ZnO crystalline structure in the photoelectrode can significantly improve current densities and consequently the photoconversion efficiency (η) of the QDSSCs, achieving maximum η of 3.4 % with five ZnO nanocubes layers with a 0.0005 M Al3+ doping concentration. While with the undoped sample and bare TiO2, the obtained ήs were 2.85 and 1.93 %, respectively. The improved QDSSC photovoltaic performance was attributed to the increased light harvesting due to a large surface area by introducing Al-doped ZnO nanocubes into the available places of the TiO2 lattice. On the other hand, the increased electrical conductivity due to the Al3+ ion doped into the ZnO lattice at the divalent Zn2+ site allows electrons to move readily into the Al-doped ZnO conduction band. Additionally, according to electron lifetime studies, the Al-doped ZnO nanocubes act as a dielectric layer, enhancing the photogenerated charge extraction process due to the introduction of lattice defects, causing intermediate levels to obtain higher electron recombination resistance.