Surface Passivation and Carrier Collection in {110}, {100} and Circular Si Microwire Solar Cells

Surface recombination is a major bottleneck for realizing highly efficient micro/nanostructure solar cells. Here, parametric studies of the influence of Si microwire (SiMW) surface-facet orientation (rectangular with flat-facets, {110}, {100} and circular), with a fixed height of 10 µm, diameter (D = 1.5–9.5 µm), and sidewall spacing (S = 2.5–8.5 µm), and mesh-grid density (1–16 mm−2) on recombination and carrier collection in SiMW solar cells with radial p-n junctions are reported. An effective surface passivation layer composed of thin thermally grown silicon dioxide (SiO2) and silicon nitride (SiNx) layers is employed. For a fixed D of 1.5 µm, tight SiMW spacing results in improved short-circuit current density (Jsc = 30.1 mA cm−2) and sparse arrays result in open-circuit voltages (Voc = 0.552 V) that are similar to those of control Si planar cells. For a fixed S, smaller D results in better light trapping at shorter wavelengths and higher Jsc while larger D exhibits better light trapping at larger wavelengths and a higher Voc. With a mesh-grid electrode the power conversion efficiency increases to 15.3%. These results provide insights on the recombination mechanisms in SiMW solar cells and provide general design principles for optimizing their performance.