Single-Component Organic Solar Cells with Competitive Performance

Yakun He,Christoph J Brabec,Ning Li

doi:10.1055/s-0041-1727234

Abstract

Organic semiconductors with chemically linked donor and acceptor units can realize charge carrier generation, dissociation and transport within one molecular architecture. These covalently bonded chemical structures enable single-component organic solar cells (SCOSCs) most recently to start showing specific advantages over binary or multi-component bulk heterojunction concepts due to simplified device fabrication and a dramatically improved microstructure stability. The organic semiconductors used in SCOSCs can be divided into polymeric materials, that is, double-cable polymers, di-block copolymers as well as donor–acceptor small molecules. The nature of donor and acceptor segments, the length and flexibility of the connecting linker and the resultant nanophase separation morphology are the levers which allow optimizing the photovoltaic performance of SCOSCs. While remaining at 1–2% for over a decade, efficiencies of SCOSCs have recently witnessed significant improvement to over 6% for several materials systems and to a record efficiency of 8.4%. In this mini-review, we summarize the recent progress in developing SCOSCs towards high efficiency and stability, and analyze the potential directions for pushing SCOSCs to the next efficiency milestone.

Highlights

Organic solar cells (OSCs) have received great attention due to multiple advantages such as high flexibility, feasible processing by roll-to-roll printing, semi-transparency and light weight applications.[1,2,3,4] In the early years, planar heterojunction (PHJ) concepts were favored where the pure donor layer and pure acceptor layer are stacked on top of each other as a bilayer
We summarize the recent progress in developing single-component organic solar cells (SCOSCs) towards high efficiency and stability, and analyze the potential directions for pushing SCOSCs to the efficiency milestone
The diversified structures of materials applied in SCOSCs will stimulate more research

Summary

Introduction

Organic solar cells (OSCs) have received great attention due to multiple advantages such as high flexibility, feasible processing by roll-to-roll printing, semi-transparency and light weight applications.[1,2,3,4] In the early years, planar heterojunction (PHJ) concepts were favored where the pure donor layer and pure acceptor layer are stacked on top of each other as a bilayer. Carrier generation and carrier separation occurred at the donor–acceptor (D–A) interface and required an energy offset as the driving force to split the excitons.[5,6,7,8,9,10] the typically short diffusion length of excitons ($10 nm) restricted the active layer thickness and led to incomplete light absorption.[11] This problem was overcome with the bulk heterojunction (BHJ)[8] concept where the donor and acceptor materials are rather homogenously mixed and percolated into an interpenetrated network.[12,13] With the development of new kinds of donor and acceptor materials, including push–pull semiconductors,[14,15] low bandgap polymers and small molecules[13,16,17,18,19,20] as well as nonfullerene acceptors (NFAs),[21,22,23,24,25,26,27,28,29] recently developed OSCs have shown efficiencies over 17%21 and the 20% milestone is within reach.[30] When we consider the practical application of solar cells, other factors, i.e., the large-scale processing feasibility and, most importantly, stability, are of equal importance as efficiency.[31,32] Highperformance BHJ OSCs benefit from a precisely adjustable compromise between sufficient interfaces for exciton dissociation and continuous pure domains for efficient charge transport. 78 P6 79 P7 80 P8 81 P9 38 P10 82 P11 83 P12 84 P13 85 P14a 86 P14b 60 P15 87 P16 39 P17a 88 P17b 57 P18a 57 P18b

44 Polymer

Conclusions and Outlook

Findings

Funding Information