미래를 창조하는 포스텍 화학공학과
Crosslinkable additive in organic solar cells has great potential to fix metastable bulk heterojunction, supplying solutions for burn-in loss and long-term instability. New roles of crosslinkable additive as a solvent additive, radical scavenger, and stretchability enhancer beyond its well-known role as a crosslinker with morphology frozen effect are reported. According to the main chain structure between -Br in end groups, crosslinkable additive is divided into two types of alkyl and siloxane main chain, expecting different roles. First, the alkyl moiety molecule, 1,8-dibromooctane (DBr-octane), provides the effects of improved thermal and light stability without any loss in efficiency. The DBr-octane device shows remarkable enhanced results in burn-in-free, maintaining 90% of its initial efficiency after 600 min at 85 °C, and light stability, maintaining 90% of its initial efficiency after 360 min under 1 SUN, in a fullerene system. Second, crosslinkable additive is treated with siloxane main chain molecule, bis(3-bromopropyl)-terminated poly(dimethyl siloxane) (DBr-siloxane), in an active layer to secure stretchability. As a result, the DBr-siloxane-treated film stretches up to 70% and the flexible device of the fullerene system maintains an initial efficiency of over 60% after 1000 bending cycles at a bending radius of 1.8 mm.