Achieving Thickness‐Insensitive Morphology of the Photoactive Layer for Printable Organic Photovoltaic Cells via Side Chain Engineering in Nonfullerene Acceptors

Abstract

Although high power conversion efficiency of over 14% has been achieved using nonfullerene acceptors (NFAs) in organic photovoltaics (OPVs), securing their insensitive device performance to the thickness of the photoactive layer remains an indispensable requirement for their successful commercialization via printing technologies. In this study, by synthesizing a new series of ITIC‐based NFAs having alkyl or alkoxy groups, it is found that the bulk heterojunction morphology dependence on the thickness of the photoactive layer becomes more severe as the difference in the surface energy of the donor and acceptor increases. It is believed that this observation is the origin that yields the device performance dependence on the thickness of the photoactive layer. Through sensitive control of the surface energy of these ITIC‐based NFAs, it is demonstrated that thickness‐insensitive OPVs can be achieved even using a doctor blade technique under air without using any additives. It is believed that present approach provides an important insight into the design of photoactive materials and morphology control for the printable OPVs using NFAs.

An Alkoxy‐Solubilizing Decacyclic Electron Acceptor for Efficient Ecofriendly As‐Cast Blade‐Coated Organic Solar Cells

“…Here, we synthesized an alkoxy‐substituted A–D–A FREA F10IC2 (chemical structure is shown in Figure a), where the decacyclic core benefited intermolecular interaction and charge transporting between molecules. The alkoxy side chains of F10IC2 not only extended the absorption of FREA due to the inductive effect of oxygen atoms, but also could greatly increase the solubility of F10IC2 relative to the alkyl‐substituted analogue, enabling the process in nonchlorinated solvents. F10IC2 showed complementary absorption and matched energy levels with the commercial polymer donor PTB7‐Th (Figure a).…”

Recent progress in thick‐film organic photovoltaic devices: Materials, devices, and processing

“…76−79 The benzodithiophenedione unit, which has high planarity and conductivity, has been widely studied in recent years, which has high crystallinity and hole mobility, and hence performs very well in a variety of NFA systems and thick-film devices. [80][81][82] Its fluorinated derivative PM6 and chlorinated derivative PM7 also show excellent performance with various NFAs such as the IDIC, 31,[83][84][85] ITIC, 31,86,87 and Y6 derivatives. 1,88-90 A wide range of polymer donors with high planarity and charge mobility have also been included in thick-film devices.…”

“…Copolymers based on fluorinated benzotriazole (FBTA) derivatives have been well studied in thick junctions 76 . − 79 The benzodithiophenedione unit, which has high planarity and conductivity, has been widely studied in recent years, which has high crystallinity and hole mobility, and hence performs very well in a variety of NFA systems and thick‐film devices 80–82 . Its fluorinated derivative PM6 and chlorinated derivative PM7 also show excellent performance with various NFAs such as the IDIC, 31,83–85 ITIC, 31,86,87 and Y6 derivatives 1,88–90 .…”

A Critical Review on Efficient Thick‐Film Organic Solar Cells

“…The charge recombination will become serious along with the increase in active layer thickness, which is mainly due to the low charge mobility of organic photoactive materials and unfavorable morphology in thick active layers. [ 35–38 ] The severe charge recombination in thick active layers will drastically decrease the FF and PCE of thick‐film OSCs. [ 39,40 ] An urgent scheme is needed to find ways to reduce charge recombination in thick active layers for achieving highly efficient thick‐film OSCs.…”