Impact of concentration variation and thermal annealing on performance of multilayer OSC consisting of sandwiched P3HT layer between PEDOT:PSS and P3HT:PCBM

Abstract

In this paper, comprehensive study on variation in composition ratio and thermal annealing of multilayer organic solar cells (OSC) has been demonstrated. Our previous work reported that in comparison to the conventional OSC structure, multilayer OSC consisting of the pure donor phase between the hole transport layer and active layer has shown a significant improvement in the power conversion efficiency (PCE). Since photovoltaic performance of the OSC strongly influenced by composition ratio, the impact of poly 3-hexylthiophene (P3HT) and 6,6-phenyl-C61-butyric acid methyl ester (PCBM) weight ratio has been analyzed. It has been found that, the short-circuit current density (JSC) of the device is highest for the P3HT:PCBM composition ratio of 1.0:0.8 and decreases slightly for 1.0:1.0 weight ratio. This study has also been accompanied with the thermal annealing on spin coated P3HT:PCBM which further enhances the PCE of the device. The maximum JSC and the PCE of 9.47 mA/cm2 and 3.26% has been achieved for the multilayer OSC having P3HT:PCBM composition ratio of 1.0:0.8 and thermally annealed at 140 °C. This is attributed largely by the tuned phase morphology of the donor-acceptor. It has been found that, the P3HT:PCBM weight ratio of 1.0:0.8 results into efficient photon absorption and charge separation in the bulk heterojunction OSC. The reduced concentration of PCBM in 1.0:0.8 weight ratio leads to the strong interchain interaction of P3HT molecules which enhances the charge separation and collection ability of the bulk heterojunction OSC.