| Solar energy harvesting demands low-cost energy conversion in the infrared from 1--2 mum. However, solution-processed photovoltaic devices have remained relatively inefficient in this spectral region.;Herein, lead sulfide colloidal nanocrystal quantum dots are used to facilitate efficient infrared power conversion. Solution-cast nanocrystal films are employed in a simple metal/semiconductor/metal architecture to produce a photovoltaic effect. It is shown that a Schottky barrier is induced, which is responsible for the charge separating action. Through optimization of chemical processes and device fabrication, the photovoltaic response is maximized. The infrared power conversion efficiency reaches 4.2%, which sets a new precedent for solution-processed photovoltaic cells. Furthermore, the devices exhibit efficient broadband solar power conversion and show promise for multijunction cell architectures. Carrier drift through a large depletion region near the Schottky contact is determined to be the dominant transport mechanism. |
