Fabrication of bulk heterojunction photovoltaic cells with controlled distribution of p-n components by Evaporative Spray deposition using Ultradilute Solution

A distribution-controlled bulk heterojunction (dc-BHJ) photovoltaic cell where the distribution of an electron donor and acceptor is controlled across the film was fabricated by Evaporative Spray Deposition using Ultradilute Solution (ESDUS) method, which can build a layered structure of polymer semiconductors soluble in a same solvent, and the energy conversion efficiency, PCE, of the dc-BHJ was significantly improved compared with a conventional BHJ cell. The dc-BHJ cells were fabricated by changing the ratio of a donor, regioregular poly(3-hexyl-thiophene-2,5-diyl) (P3HT), and an acceptor, a fullerene derivative (PCBM), from 2:1 to 1:2. The short circuit current, Jsc, and PCE of a dc-BHJ cell having P3HT-rich BHJ/PCBM-rich BHJ structure was 6.06 mA/cm² and 2.15 %, respectively, while those of a conventional BHJ cell having P3HT:PCBM=1:1 layer were 5.26 mA/cm², 1.71 %. In the dc-BHJ cells, the introduction of composition gradient brought about the increase in conversion efficiency. The transportation of photogenerated charge carriers to the collecting electrodes was improved because the better pathways should be formed in the dc-BHJ cells.