Elements of modelling and design of multi-quantum well solar cells

Multi-quantum wells structures provide some flexibility for adjusting the absorption edge of multi-junction sub-cells. In order to obtain the desirable performance, it is essential to have an accurate model of the MQW properties and of the solar cell as a whole, including the light absorption, carrier extraction and carrier collection mechanisms. In this work, we show that Shockley-Read-Hall (SRH) recombination and insufficient light absorption are the main limiting factors for achieving high currents. The former can be reduced by a smart placement of the QWs inside the structure. By leaving a gap in the MQW stack, where SRH recombination is maximum, an improvement of the current at the maximum power point can be achieved without adding QWs. Increasing their number enhances light absorption but also the thickness of the device and the difficulty for carrier transport across the QW region. In this case, knowing the background doping and the carrier mobilities help to make an optimum solar cell design. In particular, we find than an intentional, low doping might lead to higher currents with short QW stacks than using a longer ones on an intrinsic region.