Abstract
Inkjet printing (IJP) of polymer solar cells is ideal for small‐area off‐grid electronics with low power consumption. However, IJP is quite a complex technique compared with techniques such as spin coating or doctor blading. The IJP of polymer blends is reported based on ITIC derivatives as non‐fullerene acceptors (NFAs) using non‐halogenated solvents. The results show that fluorination of NFA is essential to form highly stable inks in o‐xylene, because ITIC has significantly insufficient solubility compared with ITIC‐4F. The importance of tetralin as a multifunctional co‐solvent for printing highly efficient PM6:ITIC‐4F blends is demonstrated, as even at very low concentrations, tetralin not only improves ink jettability and open nozzle time, but also improves drying behavior of the blend layer, resulting in blends with homogeneous micro‐ and nanoscale morphology. The resulting solar cells using inkjet‐printed polymer blends show a maximum efficiency of 10.1%. Moreover, IJP produces significant changes in the nanoscale and microscale morphology. In particular, the formation of a thin PM6 capping layer on the blend surface along with improved phase separation and crystallinity in both the donor and acceptor greatly reduces the recombination of charge carriers in thick blends, making inkjet‐printed photoactive films very promising for industrial applications.
Highlights
Over the last decade, the development of non-fullerene acceptor (NFA) resulted in power conversion efficiencies (PCEs) of organic solar cells (OSCs) exceeding 17%.[1,2] This advances OSCs closer to commercial applications such as powering the off-grid electronics including the Internet of Things (IoT).[3]
Systematical studies of structural, nanoscale, and electronic properties of the printed blends compared with spin-coated layers reveal that Inkjet printing (IJP) leads to clear morphological changes in terms of donor material capping layer formation at the surface and improved phase separation and crystallinity for both donor and acceptors leading to low charge carrier recombination in thick blend layers
IJP is considered as a promising technique for processing of shape-controlled digital-printed OSCs
Summary
The development of non-fullerene acceptor (NFA) resulted in power conversion efficiencies (PCEs) of organic solar cells (OSCs) exceeding 17%.[1,2] This advances OSCs closer to commercial applications such as powering the off-grid electronics including the Internet of Things (IoT).[3]. ITIC-4F has shown high compatibility with non-halogenated solvents such as o-xylene.[32] To adjust the printing parameters, inks based on pure o-xylene and o-xylene–tetralin solvent mixture were studied as demonstrated by Baran and co-workers.[22] Our results reveal that layer formation and nanoscale morphology of inkjet-printed blends depend strongly on the chemical structure of the NFA and, more importantly, on the solvent additives that allow to improve jetting and drying properties of the blend layers. Systematical studies of structural, nanoscale, and electronic properties of the printed blends compared with spin-coated layers reveal that IJP leads to clear morphological changes in terms of donor material capping layer formation at the surface and improved phase separation and crystallinity for both donor and acceptors leading to low charge carrier recombination in thick blend layers
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