CdSe quantum dots as co-sensitizers of organic dyes in solar cells for red-shifted light harvesting

Abstract

We first demonstrated an application of CdSe quantum dots (QDs) as co-sensitizers of organic dyes in solar cells with a polysulfide electrolyte for obtaining red-shifted light-harvesting. Firstly, the loading of QDs on the co-sensitized electrodes was found to have little influence on the electron transport properties, which mainly depended on the organic dye adsorption. IPCE spectra of the co-sensitized solar cells extended from 570 nm, the organic dye (JK24 and JK28) absorption threshold, to 650 nm due to the adsorption of 4.2 nm diameter CdSe QDs. Secondly, the photovoltaic performance of co-sensitized solar cells correlated significantly with the electrode architecture. With a spatially-organized electrode, on which QDs were mainly located on the back side of TiO2 film and organic dye molecules covered on the front side, the co-sensitized solar cells can maintain IPCE values as high as those obtained from the singly dye sensitized solar cells at short wavelengths of the organic dye photoresponsive region. As the result of the IPCE extension to longer wavelengths and retention at short wavelengths, the co-sensitized solar cells with QDs presented dramatically improved photocurrent and power conversion efficiency. The open-circuit voltage of co-sensitized solar cells was also improved due to an enhanced retardation of charge recombination. Although the photovoltaic performance in our system is still inferior to the best dye-sensitized solar cell system, the success in utilizing QDs as co-sensitizers open up an alternative way to the design of next-generation solar cells.