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    Key factors to improve the efficiency of roll-to-roll printed organic photovoltaics

    Year: 2013

    Journal: Organic Electronics, 14, pp 1744-1748, 20130926

    Authors: Christos Koidis, Stergios Logothetidis, Apostolos Ioakeimidis, Argiris Laskarakis, Christos Kapnopoulos

    Organizations: Aristotle University of Thessaloniki, Physics Department, Lab for Thin Films-Nanosystems and Nanometrology (LTFN), GR-54124 Thessaloniki, Greece

    In order to achieve the cost-efficient scalability of flexible organic photovoltaics (OPVs), theoptimization of key factors related to the materials and roll-to-roll (R2R) processes is necessary.The limited drying during the R2R printing process induces a vertical phase separationleading to the formation of a P3HT-rich top region on the photoactive layer which actsas an electron barrier in normal geometry. We show that the increase of R2R drying timeand/or post-annealing can enhance the OPV efficiency by the diffusion of PCBM towardsthe photoactive layer surface forming an electron transport network. It is estimated thatthe volume fraction of PCBM at the top region of the films triples from about 9% to 30%.In addition, the direct exposure of PEDOT:PSS to air after printing leads to morphologicalchanges that negatively affect the efficiency. Therefore, the protection of PEDOT:PSS fromair in combination to the increase of the R2R drying time enables the significant increase ofthe R2R printed OPVs efficiency to 1%.