Blend ratio and applied voltage effects on the charge recombination in bulk heterojunction polymer solar cells based on anthracene-containing poly(arylene-ethynylene)-alt-poly(arylene-vinylene) studied using magnetoconductance

Abstract

We have investigated the magnetic field effect on the current in bulk heterojunction polymer solar cells made of blends of an anthracene-containing poly(arylene-ethynylene)-alt-poly (arylene-vinylene) (AnE-PVstat) and fullerene molecules prepared in various ratios (1:1, 1:2, 1:3 and 1:4) and different applied voltages ranging from 0.7 to 0.95 V in steps of 0.05 V. The efficiencies and fill factors of the resulting devices improved upon increasing the PCBM content. The highest efficiency obtained was 2.7% for the device prepared using 75% PCBM. The measured magnetoconductance (MC) is positive and monotonic over the full range of the blend ratios and applied voltages studied. We analyzed the MC effect using a magnetoconductance model controlled by interconversion of the singlet and triplet (MIST) electron-hole (e-h) pairs states based on density matrix formalism using the stochastic Liouville equation considering that the singlet and triplet e-h pairs have different recombination and dissociation rates to theoretically reproduce the line shape of MC. For all the applied voltages studied, the recombination and dissociation rates of the e-h pairs on the singlet and triplet states decreased upon increasing the fullerene content until it reached a maximum with a PCBM content of 75 wt%. After this PCBM content, the rates started to increase. However, for each blend ratio, the recombination and dissociation rates of the singlet and triplet e-h pairs increase when the voltage is increased.