Recently, stamping transfer process using by thin films or soft mold has been considered by advanced technology to overcome limits of wet coating such as spin or dip coating, which are composed of deposition of large area and specific region, the material loss, and penetration of solvents. Although the adhesion energy between stamp and targets was minimized for a successful transfer process, many researches have not discussed this factor. In this research, we introduced wetting coefficient related with the adhesion energy. We investigated the adhesion energy depending on the surface energy of the stamp. We applied polyurethane acylate (PUA) as the stamp, of which the surface energy was modified to increase the transfer reproducibility. As a results, high-surface-energy PUA was used to form organic bulk hetero junction (BHJ) layer onto PEDOT:PSS/ITO substrates. The transferred device revealed a comparable efficiency, 95% relative to spin coating device. In order to find a decrease of fill factor of transferred device, we observed charge recombination and resistance through impedance spectroscopy. Second, we applied stamping transfer to formation of inter-layer in planer-type perovskite photovoltaics. We have successfully fabricated the device with transferred inter-layer, 6,6-phenyl-C71 butyric acid methyl ester (PC71BM), onto perovskite layer by dry stamping transfer condition. The device exhibited enhanced Jsc and efficiency, which were caused by improved coverage of inter-layer on perovskite layer, correlated with increased electron mobility and exciton dissociation. Finally, we fabricated organic photodetectors (OPDs) by stamping transfer process for photo sensitive BHJ layer. We confirmed a comparable performance of the transferred OPD, compared to the device from spin coating. Especially, the dry transferred device exhibited a superior durability (over 90%) for 350 hours to the spin coated device, because of morphology stabilization of photo sensitive layer, which led to suppression of degradation of the layer and burn-in loss. This work provides a promising alternative process which can improve the device operation durability without burn-in loss by a simple and controllable transfer films.
K. M. Kim, W. Jang, S. C. Mun, S. Ahn, J. J. Park, Y. Y. Kim, E. Kim, O O. Park and D. H. Wang, Org. Electron., 2016, 31, 295.
S. Ahn, W. Jang, S. Park, D. H. Wang, ACS Appl. Mater. Interfaces, 2017, 9, 15623
W. Jang, D. H. Wang, ACS Appl. Mater. Interfaces, 10.1021/acsami.8b13375