Morphology Reversal of a Non-Fullerene Acceptor Via Surface Controlled Decal-Printing Technique for Efficient Photo-Conversion and Detection in Organic Optoelectronic Device

Recently, the dry film transfer process using polymer mold has been attracted by advanced technology to overcome the limitation of the conventional wet coating process such as spin or dip coating. To demonstrate the transfer process, the soft polymer mold as process mediator is key factor. Polydimethylsiloxane (PDMS) is widely introduced to transfer the thin films previously, but it is difficult to adopt in the organic solvent filed due to the poor chemical resistance. To alternate this, polyurethane acrylate (PUA) material is introduced having proper physical and chemical property to the organic solvent such as chlorobenzene (CB) which is extensively used in organic optoelectronic devices. In this study, a novel thin film transfer technique is highlighted, named decal-printing process, using the surface controlled PUA mediator by introduced hydrophilic 2-hydroxyethyl methacrylate (2-HEMA) as reactive diluent.[2] By controlling the adhesion of the mediator based-on wetting coefficient theory, the decal-printing process is successfully demonstrated by transferring the organic photoactive layer composed of the polymer donor, poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th) and narrow bandgap non-fullerene acceptor (NFA), 2,2′-[[4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl]bis[[4-[(2-ethylhexyl)oxy]-5,2-thiophenediyl]methylidyne(5,6-difluoro-3-oxo-1H-indene-2,1(3H)-diylidene)]]bis[propanedinitrile] (IEICO-4F).[3] This process induces a sharp morphology of the thin film, prevents damage to the underlying layer by suppressing the solvent penetration because of this technique enable to dry-transfer process. Both photovoltaic cells and photodetectors prepared by the decal-printed photoactive layers containing fluorinated NFAs showed higher performance (power conversion efficiency = 10.69% and specific detectivity = 1.27 × 10¹² A cm Hz^1/2 W⁻¹, respectively) than those of devices prepared by the conventional spin-coating process owing to morphology reversal and smoother interface that led to suppressed internal resistance and enhanced charge flow in normal structure. Thus, the reproducible decal-printing process using a customized elastomeric polymer mediator is an important thin film fomration technique for efficient next-generation organic optoelectronic materials.[4]<br/><br/>[1] H. Xu, F. Qiu, Y. Wang, W. Wu, D. Yang, Q. Guo, Progress in Organic Coatings 2012, 73, 47.<br/>[2] M. S. Kim, W. Jang, S. C. Mun, B. G. Kim, D. H. Wang, J. Power Sources. 2022, 528, 231206.<br/>[3] M. S. Kim, W. Jang, T.-Q. Nguyen, D. H. Wang, Adv. Funct. Mater. 2021, 31, 2103705.<br/>[4] W. Jang, D. H. Wang, ACS Appl. Mater. Interfaces 2018, 10, 44, 38603.