Influence of deposition strategies on CdSe quantum dot-sensitized solar cells: a comparison between successive ionic layer adsorption and reaction and chemical bath deposition

Deposition and synthesis strategies of quantum dots (QDs) exert appreciable influences on the photovoltaic properties of quantum dot-sensitized solar cells (QDSCs). In this paper, a systematic characterization of morphology, optical and electrochemical properties has been carried out to correlate the assembling of QDs with the performance of the resultant QDSCs. CdSe sensitized TiO2 solar cells were investigated focusing on the influences of two commonly used in situ QD deposition methods, i.e., successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD). By applying a pre-assembled CdS seed layer prior to CdSe deposition, a power conversion efficiency up to 4.85% has been achieved for CdS/CBD-CdSe cells, which is appreciably higher than 3.89% for the CdS/SILAR-CdSe cell. TEM images revealed that CdS seeded SILAR is only capable of less than full coverage, in contrast, the CdS seeded CBD technique secures full conformal coverage of QDs on TiO2. The full conformal coverage of QDs offers two benefits, (1) high loading of QDs for efficient photon capturing, contributing to the increase of photocurrent, and (2) suppression of interfacial charge recombination, resulting in high open-circuit voltage and a large fill factor. Our success in achieving the perfect coverage of QDs based on CdS seeded CBD highlights strong implications for the performance optimization of QDSCs.