Quantum efficiency of intermediate-band solar cells based on non-compensated n-p codoped TiO2

As an appealing concept for developing next-generation solar cells, intermediate-band solar cells (IBSCs) promise to drastically increase the quantum efficiency of photovoltaic conversion. Yet to date, a standing challenge lies in the lack of materials suitable for developing IBSCs. Recently, a new doping approach, termed non-compensated n-p codoping, has been proposed to construct intermediate bands (IBs) in the intrinsic energy band gaps of oxide semiconductors such as TiO2. We explore theoretically the optimal quantum efficiency of IBSCs based on non-compensated n-p codoped TiO2 under two different design schemes. The first preserves the ideal condition that no electrical current be extracted from the IB. The corresponding maximum quantum efficiency for the codoped TiO2 can reach 52.7%. In the second scheme, current is also extracted from the IB resulting in a further enhancement in the maximum efficiency to 56.7%. Our findings also relax the stringent requirement that the IB location be close to the optimum value, making it more feasible to realize IBSCs with high quantum efficiencies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4750981]