(342c) Interfacial Modification of CdSe-Based Quantum Dot Solar Cells for Rapid Hole Scavenging

Quantum dot solar cells offer much potential to provide transformative light-harvesting and conversion technology. However, limitations in the transfer and transport of electrons and holes in these nanostructured solar cells lead to low power conversion efficiencies. In particular, even though electron transfer from CdSe quantum dots to TiO2 occurs on the order of 1010-1011 s-1, hole transfer to polysulfide electrolyte is much slower with rate constants approaching 108 s-1. The back transfer of electrons to the oxidized polysulfide species is also a hindrance in obtaining higher photocurrents. Here we present an interfacial modification of CdSe with a thin CuxS layer to serve as a hole mediator between CdSe and polysulfide, which leads to higher power conversion efficiency. Transient absorption spectroscopy was used to demonstrate the hole transfer from CdSe to CuxS. Flash photolysis further shows on longer timescales the rate of electron-hole recombination is suppressed. These results confirm the transfer of holes from CdSe to CuxS and improved charge separation are responsible for the increased power conversion efficiency.