Phenoxazine Derivative Operates as an Efficient Surface-Grafted Molecular Relay to Enhance the Performance and Stability of CdS- and CdSe-Sensitized TiO2 Solar Cells.

We report on a new phenoxazine derivative, 10-butyl-phenoxazine-3-carboxylic acid (BPCA), that we designed to operate as a molecular relay in semiconductor-sensitized solar cells (SSCs). After BPCA surface modification and in the presence of a cobalt-bipyridyl complex acting as a redox mediator, both TiO2 /CdS/BPCA and TiO2 /CdSe/BPCA SSCs exhibit enhanced photovoltaic performance and stability. In particular, the power conversion efficiencies of CdS and CdSe-based solar cells are improved by 90 % and 57 %, respectively. Furthermore, after 300 s the JSC of TiO2 /CdS/BPCA SSCs is stabilized at 30 % of its initial value, while in the same time CdS-based devices retain only 1 % of their initial JSC . The origin of the improvement arises from the excellent electron-donating property of BPCA and its role as a powerful molecular relay in non-polysulfide based SSCs.