Combining the post synthesis ligand-assisted technique and SILAR method to assemble the quantum dots onto the oxide semiconductor photoelectrodes and its applications for solar cells

Highlights: • The CdS-CdSe/CdSe QDs sensitized TiO₂ NWs was successfully prepared. • The preparation method combines PSLA and SILAR techniques for the first time. • The charge transfer dynamics was studied by SPV, TPV and TPC techniques. • The reference QDSCs of PCE is 1.73%. • The maximum PCE of 3.13% was obtained for the optimized QDSCs. The inverted type-I CdS-CdSe core-shell structure quantum dots (QDs) (denoted as CdS-CdSe QDs) applied in QDs sensitized solar cells (QDSCs) has attracted wide attention and researches due to its special photoelectric properties. But this post synthesis ligand-assisted (PSLA) technique need to assemble the previously prepared QDs onto the photoanode, leads to the low loadings of QDs and poor photoelectric performances of solar cells. Hence, we elaborately combine the PSLA technique and successive ionic layer absorption and reaction (SILAR) method to assemble the QDs onto the photoanode to improve the loadings of QDs and photoelectric properties of solar cells. The anatase TiO₂ nanowires (NWs) electrode deposited with CdS-CdSe core-shell QDs and CdSe QDs (denoted as CdS-CdSe/CdSe QDs) was successfully prepared by combining the post synthesis ligand-assisted technique and SILAR method. The surface photovoltage (SPV), the transient photovoltage (TPV) and transient photocurrent (TPC) techniques were applied to systematically study the dynamics of charge separation and transfer. These measurements demonstrate that CdS-CdSe/CdSe QDs sensitized TiO₂ NWs photoelectrodes exhibits favorable separation efficiency due to the increase of sunlight utilization. With the polysulfide electrolyte, the maximum photoelectric conversion efficiency (PCE) with the enhanced short circuit current (J_sc) of 17.76 mA/cm⁻² for the CdS-CdSe/CdSe QDs and the J_sc of 11.4 mA/cm⁻² for pure CdS-CdSe QDs were obtained under illumination at 100 mW/cm². To enhance the PCE, the TiO₂ NWs was optimized by N-doped and the optimized PCE of 3.13% with 18.22 mA/cm² of J_sc was achieved for the QDSCs deposited with CdS-CdSe/CdSe QDs.