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 TiO$_2$. We explore theoretically the optimal quantum efficiency of IBSCs based on non-compensated n-p codoped TiO$_2$ 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 TiO$_2$ 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.