Spin-enhanced organic bulk heterojunction photovoltaic solar cells

TL;DR

This paper introduces a spin-based doping method using galvinoxyl radicals to suppress polaron pair recombination in organic solar cells, significantly enhancing their efficiency by leveraging spin-flip mechanisms supported by experimental and theoretical evidence.

Contribution

It presents a novel spin doping technique with galvinoxyl radicals that reduces recombination losses and improves organic photovoltaic efficiency, supported by experimental and computational analysis.

Findings

Efficiency increased by 18% at optimal doping

Spin-flip mechanism reduces polaron pair recombination

Magneto-photocurrent and DFT support the proposed mechanism

Abstract

Recently, much effort has been devoted to improve the efficiency of organic photovoltaic solar cells based on blends of donors and acceptors molecules in bulk heterojunction architecture. One of the major losses in organic photovoltaic devices has been recombination of polaron pairs at the donor/acceptor domain interfaces. Here, we present a novel method to suppress polaron pair recombination at the donor/acceptor domain interfaces and thus improve the organic photovoltaic solar cell efficiency, by doping the device active layer with spin 1/2 radical galvinoxyl. At an optimal doping level of 3 wt%, the efficiency of a standard poly(3-hexylthiophene)/1-(3-(methoxycarbonyl)propyl)-1-1-phenyl)(6,6)C61 solar cell improves by 18%. A spin-flip mechanism is proposed and supported by magneto-photocurrent measurements, as well as by density functional theory calculations in which polaron pair recombination rate is suppressed by resonant exchange interaction between the spin 1/2 radicals and charged acceptors, which convert the polaron pair spin state from singlet to triplet.