Influence of water-soluble polythiophene as an interfacial layer on the P3HT/PCBM bulk heterojunction organic photovoltaics

Abstract

Novel HT-poly[3-(6′-N,N,N-trimethylammonium)-hexyl thiophene] (P3HTN) is developed and the use of the water-soluble thiophene as an interfacial layer for low-cost poly(3-hexylthiophene):phenyl-C61 butyric acid methyl ester (P3HT:PCBM) organic photovoltaic cells with high stability in air is investigated. When P3HTN is simply inserted between the active layer and the cathode as an interfacial dipole layer by spin-coating, the open-circuit voltage (V_oc) and short-circuit current density (J_sc) of photovoltaic cells with high work function Al metal cathodes dramatically increase. Resulting from a reduction of the metal work function and improved electron extraction efficiency, the power conversion efficiency (PCE) of the devices annealed in air is enhanced from 1.8% to 3.28%. In particular, the analogue of the active layer as a buffer layer could improve interchain interactions between the P3HT and the P3HTN to modify the interfacial contact, consequently obtaining an unattainable enhancement J_sc, with respect to the interlayer polymer replaced with an unanalogous conjugated polymer. The results would supply useful information to understand the contribution of an interfacial layer on the photovoltaic performance.