Pressure and thermal annealing effects on the photoconversion efficiency of polymer solar cells

D O Oyewole,K Kushnir,L V Titova,B Agyei-Tuffour,S A Adeniji,T Shi,O V Oyelade,W O Soboyejo,K Evans-Lutterodt,O K Oyewole

doi:10.1063/5.0045694

Abstract

This paper presents the results of experimental and theoretical studies of the effects of pressure and thermal annealing on the photo-conversion efficiencies (PCEs) of polymer solar cells with active layers that consist of a mixture of poly(3-hexylthiophene-2,5-diyl) and fullerene derivative (6,6)-phenyl-C61-butyric acid methyl ester. The PCEs of the solar cells increased from ∼2.3% (for the unannealed devices) to ∼3.7% for devices annealed at ∼150 °C. A further increase in thermal annealing temperatures (beyond 150 °C) resulted in lower PCEs. Further improvements in the PCEs (from ∼3.7% to ∼5.4%) were observed with pressure application between 0 and 8 MPa. However, a decrease in PCEs was observed for pressure application beyond 8 MPa. The improved performance associated with thermal annealing is attributed to changes in the active layer microstructure and texture, which also enhance the optical absorption, mobility, and lifetime of the optically excited charge carriers. The beneficial effects of applied pressure are attributed to the decreased interfacial surface contacts that are associated with pressure application. The implications of the results are then discussed for the design and fabrication of organic solar cells with improved PCEs.

Highlights

Organic solar cells (OSCs) have received much attention over the past three decades.1–8 This is due largely to their potential for low cost processing4,9–12 and applications in scenarios in which low cost, lightweight,3,13 flexibility,6,13–15 and stretchability16–22 are important
This paper presents the results of experimental and theoretical studies of the effects of pressure and thermal annealing on the photo-conversion efficiencies (PCEs) of polymer solar cells with active layers that consist of a mixture of poly(3-hexylthiophene-2,5-diyl) and fullerene derivative for
It has been shown that annealing of P3HT:phenyl-C61butyric acid methyl ester (PCBM) above the glass transition temperature of P3HT drives the diffusion of PCBM into the polymer matrix and promotes polymer self-organization and crystallization

Summary

Introduction

Organic solar cells (OSCs) have received much attention over the past three decades. This is due largely to their potential for low cost processing and applications in scenarios in which low cost, lightweight, flexibility, and stretchability are important. Organic solar cells (OSCs) have received much attention over the past three decades.. Organic solar cells (OSCs) have received much attention over the past three decades.1–8 This is due largely to their potential for low cost processing and applications in scenarios in which low cost, lightweight, flexibility, and stretchability are important. There is, the potential to develop low cost, lightweight, flexible/stretchable OSC structures that can harness solar energy. Since the first bi-layered OSC structures that were explored in 1986,1 OSCs have been produced largely in the form of Bulk HeteroJunction (BHJ) systems.. Since the first bi-layered OSC structures that were explored in 1986,1 OSCs have been produced largely in the form of Bulk HeteroJunction (BHJ) systems.16,27–30 These consist of mixtures of electron donors and electron acceptors that improve the transport of charges across the active layers. Tandem organic solar cells have been produced with PCEs of ∼17.3%.8

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Conclusion