Subcell Segmentation for Current Matching and Design Flexibility in Multijunction Solar Cells

Abstract

Subcell segmentation is a method to obtain nearly ideal current-matching while employing nonideal bandgap combinations in high-efficiency multijunction solar cells. By splitting each subcell into multiple semitransparent pn junctions, called segments, current-matching can be satisfied by layer design rather than material selection. This architecture replaces the standard requirement for an optimal combination of bandgaps with a simpler requirement for optimal layer thicknesses in each series-connected segment. The total device current is divided across all segments, reducing the resistive power loss especially under nonuniform illumination or high to extreme concentration. Detailed balance-based analysis of three- and four-subcell devices in both terrestrial concentrator and one-sun space applications demonstrates that the segmented architecture can approach the theoretical efficiency peak using a broad range of physically realizable bandgap combinations. For example, detailed-balance analysis reveals a 7.5%–8.1% absolute efficiency improvement for 1-cm2 segmented cells compared with standard InGaP/InGaAs/Ge designs under 1000-suns AM1.5D illumination. Higher-order segmentation multiplies the number of segments in all subcells by a common multiple, which further reduces the device current, resistive power loss, and segment thicknesses.