Device engineering for enhanced performance & stability of organic photovoltaics
The effect of metallic (free of surfactants and ligand coated) nanoparticles (NPs) incorporated into different photoactive (P3HT:PCBM, P3HT:ICBA and PCDTBT:PC71BM) and interfacial layers (TiOx) of bulk heterojunction (BHJ) organic photovoltaic (OPV) devices was systematically studied. It was evidenced that the NPs doping gives rise to photovoltaic (PV) efficiency and enhanced stability, thereby lowering device degradation rate during prolonged illumination. Spectroscopic analysis combined with photon-to-electron conversion efficiency measurements indicate that the efficiency improvement can be attributed to enhanced light harvesting and subsequent higher exciton generation rate into the photoactive layer. Therefore, this enhancement is attributed to localized surface plasmon resonant absorption (Au NPs) and scattering effects (Al NPs). Furthermore, it was demonstrated that the device performance was improved only in the case that metal NPs were in close proximity or even better in direct contact with polymer donor (bare or coated with the same ligand as the donor material). On the other hand, the introduction of Au nanorods (NRs) inside the TiOx back contact interfacial layer acts as a mirror in the device structure, increasing exciton generation through back contact scattering and thus charge collection. The most efficient cells produced in this work incorporating Au NRs into TiOx transport layer of a PTB7:PC71BM based photoactive layer, demonstrated power conversion efficiency (PCE) of 8.25 %, with Jsc of 17.46 mA/cm2, Voc of 0.76V and FF of 0.62.