Efficient photovoltaic energy conversion in tetracene-C60 based heterojunctions

We report organic solar cells fabricated with small-molecule organic semiconductor tetracene∕C60 heterojunction as the photoactive layer. The external power conversion efficiency of the devices under AM 1.5 solar illumination at 100mW∕cm2 (1 sun) is 2.3±0.5% with relatively high open-circuit voltage (Voc=0.58±0.06V) compared to most of the other small-molecular donor-acceptor (D-A) heterojunction solar cells reported so far. Using atomic force microscopy and x-ray diffraction we found that tetracene thin films consist of submicron-sized grains with rough surface and well defined molecular order. Therefore, using high mobility polycrystalline tetracene thin films for D-A heterojunction devices dramatically increases area of tetracene and C60 interface for exciton diffusion to reduce the recombination.