SUMMARY Conventional and inverted organic solar cells of poly[9,9‐dioctyl‐fluorene‐co‐bithiophene] (F8T2) as liquid‐crystal semiconducting polymer and fullerene as electron acceptor were fabricated and characterized. An effect of thermal treatment of the films on annealing condition near glass transition was investigated for tuning optimization and improving the photovoltaic and optical properties. Annealing treatment below the glass transition improved the photovoltaic performance and carrier diffusion in crystal growth of active layer. The X‐ray diffraction patterns indicate a crystalline structure with molecular order of F8T2 in crystal index, 100 as a layer distance between sheets of F8T2 chains. The photovoltaic properties were based on molecular interactions with molecular ordering in active layer at crystal state. As the photovoltaic mechanisms, the F8T2 thin film as p‐type semiconducting polymer worked for electron‐donor layer to support light‐induced generation, carrier diffusion and charge transfer near interface in active layer. Copyright © 2014 John Wiley & Sons, Ltd.

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[6,6]-phenyl C 61-butyric acid methyl ester (PCBM) and poly(3-hexylthiophene) (P3HT) bulk heterojunction solar cells added with zinc-tetra-tertiary-butyl-phthalocyanine (ZnPc) and 1,8-diiodooctane (DIO) were fabricated and characterized. Incident photon-to-current conversion efficiencies in the range of 400-650 nm were increased by the ZnPc addition, and the absorption range of ZnPc overlapped with the photoluminescence range of P3HT. Photovoltaic properties of the solar cells with an inverted structure were improved by the ZnPc and DIO addition. Microstructures of the thin films were analyzed by X-ray diffraction. The improvement would be due to the Förster energy transfer mechanism the direct charge transfer from ZnPc to PCBM, and the phase separation of PCBM and P3HT by the DIO addition would also contribute the improvement.

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Fullerene-based photovoltaic devices with an inverted structure containing silicon 2,3naphthalocyanine bis(trihexylsilyloxide) (SiNc) were fabricated and characterized. SiNc worked as a donor material, and showed optical absorption at ~800 nm. C60 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were used as acceptor materials, and C60 or PCBM/SiNc system solar cells showed incident photon to current conversion efficiency in the range of 700~800 nm. The PCBM/SiNc solar cell provided high open circuit voltage of 0.74 V. From the energy level diagram, the higher lowest unoccupied molecular orbital level of PCBM contributed to the high open circuit voltage. The surface roughness at the C60/SiNc interface is larger compared to that at the PCBM/SiNc interface, which resulted in the high short circuit current density of the C60/SiNc solar cell.