Interfacial polymer ferroelectric dipole induced electric field effect on the photovoltaic performance of organic solar cells

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Abstract
Effect of a dipolar electrical field on the photovoltaic properties of polymer solar cell devices in the bulk heterojunction structure based on 1:1 blend of donor-regioregular poly(3-hexylthiophene), P3HT, and acceptor-phenyl-C61-butyric acid methyl ester, PCBM, polymer semiconductor material is studied. With a thin layer of poled ferroelectric P(VDF + TrFE) copolymer film having oriented dipoles inserted at the interface between poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and the P3HT:PCBM composite layer, significant improvement in the short-circuit photocurrent and open circuit voltage was observed consistent with the increase in the poling voltage. Remnant polarization charge due to dipoles produces localized electric field of 300–700 V · μm−1. The presence of the electric field helps increase the charge transfer exciton dissociation rates at the P3HT (donor)–PCBM (acceptor) interfaces, reduces the exciton recombination probability and increases the carrier extraction yield resulting in the enhancement in the photocurrent. Solar cell device in a structure having a poled P(VDF + TrFE) copolymer film sandwiched between the two P3HT:PCBM composite layers shows only a marginal improvement in the photovoltaic properties. This is mainly attributed to shielding of dipolar field from free charge carries and the inferior nanoscale morphology of the P3HT:PCBM composite layer.

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