In this study, for the first time, the quaternary Cu2AgInSe4 (CAISe) quantum dots (QDs) were synthesized in an aqueous solution using the chemical precipitation method at 90 ◦C. It was observed that increasing the heating time led to a redshift in the absorption edge wavelength and a decrease in the band gap energy. The synthesized QDs, subjected to different heating durations ranging from 1 to 5 h, were employed as light absorbers in quantum dots sensitized solar cells (QDSSCs). The best performance was achieved for the QDSSC with a TiO2/CAISe(1 h)/ ZnS photoanode, yielding a power conversion efficiency of 1.72 %. It is worth noting that in this study, a ZnS blocking layer was applied to all photoanodes. Subsequently, to enhance the power conversion efficiency, a CdS nanoparticles layer was deposited on the TiO2 mesoporous sublayer using a successive ionic layer adsorption and reaction (SILAR) method. Considering the alignment of the conduction and valence band edges of CdS and CAISe, the CdS layer is deposited first, followed by formation of the CAISe layer. For comparison, each QD was also deposited individually on TiO2 to evaluate its photovoltaic response. Then, different photoanode structures i.e., the TiO2/CdS(Xc)/CAISe/ZnS, (X = 1–8), photoanodes were fabricated and applied in corresponding QDSSCs. It was observed that the highest power conversion efficiency (PCE) of 4.0 % was achieved by the cell with the TiO2/ CdS(7c)/CAISe/ZnS photoanode.
