Abstract

The nanoimprinting of polymer solar cells via soft lithography is an attractive approach for enhancing light absorption in the active layer. Many efficient polymer solar cells utilize a high boiling point solvent additive such as 1,8-diiodooctane (DIO) during active layer deposition to optimize morphology. By studying active layer films based on the PTB7-Th:PC71BM system prepared with different amounts of the solvent additive DIO, it is shown that the soft imprinting of such blends critically relies upon the presence of residual solvent additive that plasticizes the film. In particular, a minimum of ∼ 2 volume % of DIO in the casting solution is found to be necessary to enable effective imprinting. The microstructure of imprinted layers is also comprehensively characterized using atomic force microscopy, grazing incidence wide-angle X-ray scattering and resonant soft X-ray scattering, demonstrating that soft lithography can be used to effectively impart structure on the a photonic length scale without changing the nanoscale morphology and microstructure.

Highlights

  • The direct conversion of solar energy to electricity is becoming an increasingly important means of generating clean, renewable energy

  • The invention of the bulk heterojunction (BHJ) architecture is regarded as a milestone in the development of organic photovoltaic (OPV) technology,4–6 whereby an interpenetrating network of donor and acceptor phases is spontaneously formed during the solution deposition of a blend film

  • The power conversion efficiency (PCE) of organic solar cells based on polymer/fullerene blends has exceeded 10%,12–16 with the development of highperformance non-fullerene acceptors pushing the efficiency of polymer solar cells beyond 13%

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Summary

Introduction

The direct conversion of solar energy to electricity is becoming an increasingly important means of generating clean, renewable energy. Through the development of OPV technology, several effective methods have been developed to optimise nanoscale phase separation including solvent annealing, thermal annealing and solution additives.. The power conversion efficiency (PCE) of organic solar cells based on polymer/fullerene blends has exceeded 10%,12–16 with the development of highperformance non-fullerene acceptors pushing the efficiency of polymer solar cells beyond 13%.17–19. Despite these promising improvements, the low efficiency of organic solar cells compared to other photovoltaic technologies is still an aspect that is hindering their commercialization Through the development of OPV technology, several effective methods have been developed to optimise nanoscale phase separation including solvent annealing, thermal annealing and solution additives. In recent years, the power conversion efficiency (PCE) of organic solar cells based on polymer/fullerene blends has exceeded 10%,12–16 with the development of highperformance non-fullerene acceptors pushing the efficiency of polymer solar cells beyond 13%.17–19 Despite these promising improvements, the low efficiency of organic solar cells compared to other photovoltaic technologies is still an aspect that is hindering their commercialization

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