Charge separation dynamics in a narrow band gap polymer-PbS nanocrystal blend for efficient hybrid solar cells.

We have demonstrated efficient hybrid solar cells based on lead sulfide (PbS) nanocrystals and a narrow band gap polymer, poly[{2,5-bis(2-hexyldecyl)-2, 3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl}-alt-{[2,2′-(1, 4-phenylene)bis-thiophene]-5,5′-diyl}], (PDPPTPT). An opportune mixing of the two materials led to the formation of an energetically favorable bulk hetero-junction with a broad spectral response. Using a basic device structure, we reached a power conversion efficiency of ∼3%, which is one of the highest values reported for this class of solar cells. Photo-physical measurements carried out on the device provided insights into the working mechanism: the comparison between the time decay of the pristine polymer and the polymer-PbS blend allows us to conclude that efficient charge transfer is taking place in this hybrid system.