Quantum dot loading in strong alkaline: improved performance in quantum-dot sensitized solar cells

For the first time, we demonstrate that the conversion efficiency of CdTe quantum-dot sensitized solar cells could be effectively improved by using a strong alkaline environment during deposition of quantum dots (QDs) onto the TiO2 mesoporous electrode. Alkalis play three unique roles during the deposition: (i) decreasing the inter-particle electrostatic force between TiO2 nanoparticles and QDs to improve QD deposition; (ii) spontaneous formation of Cd(OH)(2) during the deposition, which contributes to improvement of device efficiency; (iii) enhancing QD stability by hindering ligands' detachment from QD surface. With these advantages, improved QD loading onto a TiO2 photoanode has been achieved, from barely loading to dense, uniform QD loading with an optimized NaOH addition. Using this method, the overall efficiency of CdTe sensitized solar cell exceeds 2.1% when coupled with a Cu2S cathode-an almost 40% increase of efficiency compared with QDs deposited under a relatively low pH environment.