  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. In this work, 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 an absorption enhancement twice 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.
