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Junwoo Lee1 Taewan Kim1 Guan-Woo Kim1 Minjun Kim1 Taiho Park1

1, Pohang University of Science and Technology, Pohang, , Korea (the Republic of)

Existing hole transport material in perovskite solar cells has only been applied to toxic solvents such as chlorobenzene due to solubility problems. These solvents result in limitation for the practical use. Therefore, substitution to non-halogen solvents is important to commercialize organic eletctronics. Here, we studied on asymmetric alkyl substitution to approach high efficient polymeric semiconductors with green processing. The concept resulted in asymmetry in the monomer itself, leading to irregularity, disturbing molecular packing. We synthesize and characterize asymmetric polymer named asy-PBTBDT and fabricate hole transport layers of perovskite solar cells using applicable green solvents from Hansen solubility parameters. The green solvent is named 2-methyl anisole that is used in food additives, which is edible and no harmful in human body. The device using asymmetric polymer leads to a PCE of around 20 % using food additive solvent (2-MA) with additives (Li-TFSI and t-BP) and a PCE of 18 % without additives Furthermore, the polymeric HTM leads to longer stability than common spiro-OMeTAD. The polymeric HTM may be a promising material to replace spiro-OMeTAD due to a green processing process for commercialization, stability and high efficiency.

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