Solution-processed infrared photovoltaic devices with >10% monochromatic internal quantum efficiency

Large-area, physically flexible, solution-cast photovoltaics are of urgent interest to realize low-cost solar cells. Polymer, polymer-fullerene, and polymer-nanocrystal photovoltaics absorb light only to wavelengths as long as 750 nm, with the exception of one recent report out to 1000 nm. Half of the sun's power spectrum lies beyond 700 nm; one third beyond 1000 nm; and infrared emitters of growing interest in thermal photovoltaics emit predominantly in the 1-3 μm range. We report herein a processible infrared photovoltaic device active beyond 1 μm. Our best devices exhibit external quantum efficiencies exceeding 1% and estimated monochromatic internal quantum efficiencies greater than 10%. This represents an improvement by more than 1000 compared to the best previously reported processible >1 μm infrared photovoltaics. We employ a novel device architecture in which the infrared-absorbing active layer is based purely on semiconductor nanoparticles with no semiconducting polymer matrix. The replacement of a polymer-quantum dot composite with a pure nanoparticle layer, combined with improvements in control of organic ligands passivating nanoparticle surfaces, facilitates improved electronic transport, enhancing carrier extraction prior to recombination.