Ideal p–n Diodes from Single-Walled Carbon Nanotubes for Use in Solar Cells: Beating the Detailed Balance Limit of Efficiency

Though many technologies exist for improving solar cell efficiencies, there remains an unexplored fundamental parameter, the diode ideality factor (n), that we can exploit. The Shockley–Queisser limit states that the maximum solar conversion efficiency in a single p–n junction is achievable only when it is operated in the ideal diode limit of n = 1. Generation and recombination losses correlate directly to an increase in the dark saturation current and n, both of which have competing effects on the open-circuit voltage. Here, we demonstrate a new approach to improving the efficiency of solar cells beyond the detailed balance limit by gate modulation of the diode’s ideality factor in ideal carbon nanotube p–n diodes. We show that the open-circuit voltage can be tuned in direct proportion to n without impacting the reverse bias leakage current or the short-circuit current. We show that our approach is similar to the enhancement from solar concentrators without actually using them. We achieve an open-circuit voltage that is ∼300% higher than that given by the detailed balance limit.