Polymer solar cells: P3HT: PCBM and beyond

For the last two decades, polymer solar cells (PSCs) have been a cynosure of the photovoltaic community, as evidenced by the growing number of patent applications and scientific publications. Efforts to achieve high power conversion efficiency in PSC, propelled by advances in device architecture, material combination, and nanomorphology control, evolved into poly(3-hexylthiophene-2,5-diyl) (P3HT): phenyl-C61-Butyric-Acid-Methyl Ester (PCBM) bulk heterojunction PSCs, which had been the best seller in PSC research for a decade. Subsequently, PSC research was redirected towards the synthesis of low bandgap materials and optimization of tandem cells, which led to a power conversion efficiency of similar to 13%. Even though this efficiency may not be sufficient enough to compete with that of inorganic solar cells, unique properties of PSCs, such as mass roll-to-roll production capability, as well as flexibility and lightness, suggest their niche market opportunities. In this review, an overview of developments in PSCs is presented during the last three decades encompassing pre- and post-P3HT: PCBM era. Emphasis is given on evolution in device architecture, coupled with material selection for pre-P3HT: PCBM era, and synthesis of low-bandgap materials, coupled with a tandem structure for post-P3HT: PCBM era. Last but not least, efforts toward the longer operational lifetime of PSCs by encapsulation are reviewed. Published by AIP Publishing.