B-S Bae, H-G Im, J. Jung
Keywords: flexible substrate, glass-fabric reinforced plastic (FRP), transparent conducting electrode (TCE), siloxane hybrid material, flexible electronics
Summary:To realize the flexible electronics in place of rigid electronics constructing on PCB substrates or glass substrates, robust film substrate with thermal resistance, strength and low thermal expansion should be developed. Specially, some applications of displays and photovoltaics, transparency is a critical requirement. Optically transparent glass-fabric reinforced plastic (GFRHybrmer) films were developed by impregnating with refractive index matched siloxane hybrid resin. GFRHybrimer films are transparent and low birefringence to be used in the displays. These show low thermal expansion coefficient (10GPa) with high thermal stability up to 350oC. Thus, these can be used as the transparent film substrates for flexible displays and electronics. We have successfully fabricated some flexible devices such as oxide TFT, OLED, and OPV on the GFRHybrimer film to confirm its feasibility. Furthermore, flexible transparent conducting electrode (TCE) substituting indium tin oxide (ITO) film is an essential component for flexible or stretchable opto-electronics. Metal (Ag or Cu) nanowire or nanotough was embedded on the surface of GFRHybrimer film during its compressing process. The fabricated TCE film is composed of a glass-fabric reinforced transparent composite film as the basal substrate and random networks AgNW and CuNW that are monolithically embedded on the film surface. The resulting hybrid structure of the metal NW-GFRHybrimer films represents exceptionally smooth surface roughness (rms ~ 1nm), good thermos-mechanical performance (Tg-less characteristic), and excellent opto-electrical performance (low resistivity and high transparency). Also, the embedment of metal NW in the thermally and chemically robust siloxane resin matrix makes the films to have excellent stability against heat, thermal oxidation and wet chemicals. Thus, the transparency and resistivity of the TCE films are strongly durable during long-term high temperature annealing. In addition to the metal NW on the surface of the GFRHybrimer films, crystalline ITO thin film or metal grid is added to fabricate hybrid TCE. The hybrid structure can enhance the conductivity to be applicable high performance flexible electronics. Using the TCE films based on GFRHybrimers, flexible devices such as OLED, OPV and perovskite solar cell were fabricated to show comparable performances to those fabricated on TCE glass substrate. Recently the flexible perovskite solar cell on c-ITO/Ag NW/GFRHybrimer film was fabricated and exhibits power conversion efficiency (PCE) of approximately 14%. Based on the results, it is expected the robust GFRHybrimer based film can be a promising high performance substrate platform for fabrication of various flexible opto-electronic devices.