Epitaxially grown quantum well and quantum dot solar cells suffer from weak light absorption, strongly limiting their performance. Light trapping based on optical resonances is particularly relevant for such devices to increase light absorption and thereby current generation. Compared to homogeneous media, the position of the quantum layers within the device is an additional parameter that can strongly influence resonant absorption. However, this effect has so far received little attention from the photovoltaic community. We develop a theoretical framework to evaluate and optimize resonant light absorption in a thin slab with multiple quantum layers. Using numerical simulations, we show that the position of the layers can make the difference between strong absorption enhancement and completely suppressed absorption, and that an optimal position leads to a resonant absorption enhancement two times larger than average. We confirm these results experimentally by measuring the absorption enhancement from photoluminescence spectra in InAs/GaAs quantum dot samples. Overall, this work provides an additional degree of freedom to substantially improve absorption, encouraging the development of quantum wells and quantum dots-based devices such as intermediate-band solar cells.
Quantum-dot solar cells are a promising high-efficiency concept, but suffer from low absorption. Resonant light trapping can enable to absorb most of the incident light while maintaining good device quality. In this paradigm, the absorption depends critically on the vertical position of the quantum dot layers, but this has been largely ignored so far (this also applies to quantum wells). Here, we show the importance of the position of 10 InAs layers in a GaAs Fabry-Perot cavity. We then extend this approach to multi-resonant absorption, showing the potential absorption gain from optimizing the position of quantum dots in full devices.
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