The origin of efficiency enhancement of inorganic/organic Hybrid solar Cells by robust samarium phosphate nanophosphors

An effective energy level regulation of acceptor by doping samarium phosphate nanophosphors (SmPO4 NPs) was reported for inorganic/organic hybrid solar cell applications. SmPO4 NPs doped TiO2/P3HT bulk heterojunction (BHJ) solar cell shows an enhanced power conversion efficiency of approaching 3% as compared with that of its counterpart without SmPO4 NPs (1.98%). The underlying photophysical mechanism was probed by applying femtosecond transient absorption spectroscopy and the results show that the efficiency enhancement was ascribed to the improved hot electron, less energetic electron, hole transports at the interface of BHJ apart from down-conversion photoluminescence of SmPO4 NPs. It has been evidenced that the hot electron transfer life time was shortened by more than 40% (i.e., from tau(hot-e)=30.2 to 17.9 ps) than pure TiO2 acceptor while the hole transfer lifetime was boosted by almost 20% (i.e., from 6.92 to 5.58 ns). Such charge carrier improvements stem from the efficient energy level regulations by SmPO4 NPs. In detail, the conduction band (CB) edge of TiO2 has been elevated by 0.57 eV while the valence band (VB) edge has been elevated by 0.32 eV, thus not only narrowing down the energy offset between CB energy levels of acceptor TiO2 and donor P3HT, but also meanwhile enlarging the band gap of TiO2 itself that permits to inhibit electron-hole recombination within TiO2. This work demonstrates that samarium ions can efficiently facilitate exciton generation, dissociation and charge transport and have an important role in enhancing photovoltaic performance. (C) 2014 Elsevier B.V. All rights reserved.