Electron Injection from a CdS Quantum Dot to a TiO2 Conduction Band as an Efficiency Limiting Process: Comparison of QD Depositions between SILAR and Linker Assisted Attachment

Sensitization of TiO2 by semiconductor quantum dots (QDs) initiates a primary charge separation in semiconductor quantum dot sensitized solar cells (QDSSCs), and thus is a key fundamental process controlling their solar cell performance. However, despite extensive researches on QD deposition methods, correlation between the solar cell performance and charge transfer dynamics modulated by the different deposition method has rarely been studied. Here, we demonstrate influence of a CdS QD deposition method on their solar cell performance and charge transfer dynamics. Two deposition methods, (i) in-situ QD synthesis directly on the TiO2 surface using a Successive Ionic Layer Adsorption and Reaction (SILAR) method, SILAR-CdS/TiO2, and (ii) linker assisted attachment of pre-synthesized QDs on the TiO2 surface, PSM-CdS/TiO2, were investigated. The electron injection efficiency of SILAR-CdS/TiO2 is estimated to be 96%, while that of PSM-CdS/TiO2 is 40 similar to 50%. The charge recombination dynamics are similar for both films Therefore, the QDSSC efficiency is essentially controlled by the electron injection process from a CdS QD to the TiO2 conduction band.