Fig. 1: Current spectrum calculated in a thin film (180 nm) GaAs solar cell. The corresponding PCE is 8.8%. In addition to the expected positive current we show a negative contribution at the device edges (labeled as LEC for Large Energy Contribution). Carriers generated at energy larger than the junction barrier are less sensitive to electric field and may diffuse in the wrong contact.
Third-generation solar cells based on quantum effects represent promising candidates to overcome the Schockley-Queisser limit. Most of the solar cell simulations consider carrier transport from a semi-classical point of view. However, semi-classical models are no longer suitable to describe electronic transport in nano-structured devices. So far, few quantum simulations have been reported. These models, computationally challenging, have been applied to specific studies with generally a monochromatic incident light. However, assuming the entire sun spectrum is essential to model solar cells and calculate the power conversion efficiency (PCE). We present a quantum transport model considering the black-body spectra for the incident light. Inspired by the excellent results achieved by Alta Device, we focus on thin GaAs p-i-n junctions. We analyze the different negative contributions to photovoltaic (PV) current versus the applied voltage. This work is the first step towards the study of nano-scale solar cells.
Fig. 2: Our theoretical approach permits to show a reduction of LEC (see Fig. 1) due to the use of AlGaAs in p-type contact. The corresponding barrier in conduction band reflects a part of electron diffusing in the wrong direction and then PCE is increased (10%).