Reducing the excess energy offset in organic/inorganic hybrid solar cells: Toward faster electron transfer

The photoexcited electron transfer rate represents one of the most important properties required for photovoltaic devices. However, the fabrication of solar cells with a faster electron transfer remains a technological challenge. Regulating the energy level alignment of acceptor-donor system by the incorporation of foreign ions is one of the most promising strategies to achieve this aim. Herein we demonstrate that the incorporation of silver ions into TiO2 nanocrystals results in a remarkable reduction of energy offset between the conduction band edge of acceptor and the lowest unoccupied molecular orbital of donor. In particular, the electron transfer life time was shortened from 30.2 to 18.3 ps, i.e., almost 40% faster than pure TiO2 acceptor, thus leading to a notable enhancement of power conversion efficiency by almost 38% in organic/inorganic hybrid solar cells. The reduction of the 'excess' energy offset accelerates the electron transfer, which is expected to have an important role in applications of solar energy conversion and photon detectors. (C) 2014 Elsevier B.V. All rights reserved.