Comparing Front- and Rear-Junction GaInP Photovoltaic Devices Through Detailed Numerical and Analytical Modeling

Achieving record efficiencies in multijunction and spectrally split photovoltaics requires maximal performance in wide-bandgap top junctions. Recent advances in single-junction wide-bandgap GaInP photovoltaic devices have been driven by a rear-junction design, in which the p-n junction is placed near the back contact. This approach is the opposite of usual front-junction designs and is also counterintuitive since carriers are now generated further away from the space charge region. In this paper, we aim to understand the advantages and disadvantages of rear-junction designs from both numerical and analytic perspectives. This allows us to point out the tradeoffs between the two photovoltaic device configurations and to generically identify the parameters where the optimal configuration flips. This understanding explains the historical development of GaInP photovoltaic technology and helps predict the most promising paths toward further improvements. Our general approach may also aid in designing other thin-film photovoltaic devices.