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

Abstract 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 (SiO 2 ) and silicon nitride (SiN x ) layers is employed. For a fixed D of 1.5 µm, tight SiMW spacing results in improved short‐circuit current density ( J sc = 30.1 mA cm −2 ) and sparse arrays result in open‐circuit voltages ( V oc = 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 J sc while larger D exhibits better light trapping at larger wavelengths and a higher V oc . 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.