Physics and design for 20% and 25% efficiency nanowire array solar cells

Bottom-up fabricated single-junction III-V nanowire array solar cells have shown efficiency up to 15.3%, which is approximately half of the conventional Shockley-Queisser detailed balance efficiency limit of 33.6%. Here, based on numerical and analytical opto-electronics modeling and analysis, we give guidelines for (i) geometry that gives strong absorption as well as (ii) the design of efficient p-n junction and electrical contacts in the nanowires to reach 20% and 25% efficiency. We exemplify the impact of eight different optical and electrical loss mechanisms in a 15% and a 25% design. We also provide an analytical equation for estimating the efficiency drop due to resistive losses in the top contact layer for varying cell size.