Columnar Structure in Bulk Heterojunction in Solution-ProcessableThree-Layered p-i-n Organic Photovoltaic Devices Using TetrabenzoporphyrinPrecursor and Silylmethyl60fullerene

摘要

Organic photovoltaic (OPV) devices based on the single activelayer bulk heterojunction (BHJ) concept~1 offer a realistic possibilityof low-cost photoenergy conversion systems.~2However, there aretwo issues that need to be resolved: One is the rather narrowrepertoire of materials,~3especially acceptor materials, and the otheris the lack of precise structural information on the BHJ layer, theheart of the device,~4where photoexcitation and charge separationoccur.~5The presumed structures of an ideal BHJ are the following:the BHJ should consist of interdigitated donor and acceptormolecular aggregates,~6and the aggregates should be comparablein size to the exciton diffusion length.~7 We report here that a newsolution-processable, small-molecule based fabrication processallows us to obtain a three-layered p-i-n structure~8in which the i-layer possesses a clearly defined interdigitated structure formedby spontaneous crystalline phase separation during thermal process-ing. This device shows a power-conversion efficiency (PCE) of5.2, a value that ranks among the best of those reported forsolution-processed small-molecule based OPV cells.~9