Solution processed p-i-n solar cells based on P3HT:PCBM bulk heterojunctions

A high potential development in organic photovoltaic technology is the production of p-i-n structure, through the controlled doping of the active layer regions close to the electrodes. Here, an opening study on p-i-n structure formation by electrochemical doping with ionic liquids, namely 1-butyl-3-methylimidazolium hexafluorophosphate and tetra-n-butylammonium tetraphenylborate, on the P3HT:PCBM system was done. We demonstrate the possibility to increase the PCE of the device, even though a decrease of performance is also shown before the proposed formation of the p-i-n structure. The IL addition produces large changes in the morphology of the film before biasing. Upon formation of a p-i-n structure, a reduction of the non-geminate recombination and an increase of the charge carriers mobilities are observed. Active layer s thickness, ionic liquid concentration and nature of the ionic liquid are parameters that must be optimized in order to further increase PCE.