Bulk Heterojunctions Based on Native Polythiophene

Three different bulk heterojunctions were prepared by solution processing from the same precursor film. The procedure employs standard film-forming processing methods from solution whereby bulk heterojunctions of poly-(3-(2-methylhexan-2-yl)-oxy-carbonyldithiophene) (P3MHOCT) and the fullerene derivatives [60]PCBM or [70]PCBM were prepared. The films were subjected to temperatures of 200 °C whereby P3MHOCT is converted to the more rigid and insoluble poly-3-carboxydithiophene (P3CT); films subjected to a temperature of 310 °C lead to decarboxylation of P3CT giving native unsubstituted polythiophene (PT). The same precursor film prepared by standard solution processing thus gave access to three chemically different bulk heterojunctions that were studied in terms of performance and stability. The device with a bulk heterojunction of PT/[70]PCBM and an active area of 3 cm 2 showed the best efficiency of 1.5% (1000 W m −2, AM1.5G, 70 °C) as well as a slow decay of the performance over 500 h of continuous illumination in a nitrogen atmosphere (330 W m −2, AM1.5G, 25 °C).