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

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 inter-conversion 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.

Automated summary

The study showed that increasing the fullerene content in the blend improved the efficiencies and fill factors of the bulk heterojunction polymer solar cells. The highest efficiency was achieved with 75% PCBM. The magnetoconductance was found to be positive and monotonic across different blend ratios and applied voltages.