Parametric study of micropillar array solar cells

Micro/nano pillar arrays are a promising architecture for high-efficiency solar cells that employ inexpensive photovoltaic materials with short minority carrier diffusion lengths (L _{n, p}). To investigate design tradeoffs of the radial junction array solar cells, we fabricated 25 μm tall c-Si pillar array devices having different diameters and pillar filling ratios. The high-aspect-ratio radial n ⁺-p ⁺ junctions were formed by gas phase diffusion of an n-type dopant into etched p-type Si pillars. The c-Si pillar arrays showed clear rectifying properties. The spectral reflectance decreased as the pillar filling ratio increased from 0.2 to 0.5, and no subsequent decrease was observed above a filling ratio of 0.5. Approximately two times higher cell efficiency was obtained with an 8 μm diameter (<1 L _n) pillar array than with a 32 μm diameter (>3 L _n) pillar array having the same pillar filling ratio.