The effect of Al electrodes on the nanostructure of poly(3-hexylthiophene): Fullerene solar cell blends during thermal annealing

The presence of Al electrodes on P3HT:PCBM blended thin films significantly modifies the structure of the films during thermal annealing processes used to produce organic photovoltaic cells. In the absence of an Al electrode, thermal annealing produces very thin (0.7 nm) P3HT layers with face-on molecular stacking near the surface of the film and vertically oriented rod-like P3HT crystals in the bulk region with edge-on molecular stacking. Thermal annealing in the presence of an Al electrode makes the preferred orientation of P3HT crystals in the films less prevalent, and Al diffuses into the organic films to form an intermediate layer. The absence of very thin P3HT layers and the less favorable P3HT orientation help to form interpenetrating networks in the organic layer, resulting in better device performance in the films annealed with Al electrodes.