InGaN Quantum Dot Superlattices as Ratchet Band Solar Cells

In this article, we investigate the construction of ratchet band solar cells using InGaN quantum dots. The strong piezoelectric potentials can spatially separate electron and hole states. This spatial separation reduces both radiative and nonradiative recombination within the quantum dot, providing one of the key characteristics of a ratchet band system. Ratchet band solar cells have proven difficult to realize experimentally, and the piezoelectric potential in InGaN quantum dots could provide a spatial ratchet that can operate at room temperature with broadband absorption. We use a
$\mathbf {k}{\cdot }\mathbf {p}$
model to calculate the electronic structure and absorptance of a superlattice of InGaN/GaN quantum dots. We present an improved method to calculate the absorptance for the bound-to-continuum transition by using bulk
$\mathbf {k}{\cdot }\mathbf {p}$
states to approximate the host material continuum states. We show an example dot structure that could act as a ratchet band solar cell. Using the absorptances of the quantum dot array, we calculate a detailed balance efficiency of 36% for the system. Optimizing the dot geometry and alloy fraction allows detailed balance efficiencies up to 42% but at the cost of losing the spatial ratchet.