The improvement on the performance of quantum dot-sensitized solar cells with functionalized Si

Quantum dots (QDs) have been attractive recently with their multiple exciton generation characteristics. QD solar cells can more effectively use the incident energy because one or more electrons are generated with the photon of high energy. They have less heat loss and higher theoretical efficiency (44%) than single exciton generation solar cells (33%). This work focused on Si as alternative to conventional QD materials. Si has QD's unique characteristics such as the quantum size effect and quantum confinement with non-toxicity and abundance. Si QDs were fabricated by the multi-hollow discharge plasma chemical vapor deposition and applied to QD-sensitized solar cells (QDSCs). Contrary to the good characteristics of Si QDs, Si QDSCs had poor performance as compared with conventional QDSCs because of the weak combination between Si QDs and TiO2. Small amounts of adsorbed Si QD on TiO2 made low photocurrent and TiO2 surface widely exposed to redox electrolyte caused charge recombination, the decrease of open-circuit voltage, and low fill factor. For improving their combination, Si QDs were functionalized. The electron transfer from Si to TiO2 and the bonding with TiO2 were improved and more Si QDs were adsorbed by the functionalization. In the functionalization process, the linking source is one of the key parameters. Therefore, 4-vinylbenzoic acid was controlled and its effect was analyzed. The change in the photovoltaic parameters according to the concentration of 4-vinylbenzoic acid and the performance dependence were investigated. In order to verify their characteristics, the effects in terms of the photovoltaic performance, electrochemical impedance, and optical properties were examined.