Revealing molecular conformation-induced stress at embedded interfaces of organic optoelectronic devices by sum frequency generation spectroscopy.

Interface stresses are pervasive and critical in conventional optoelectronic devices and generally lead to many failures and reliability problems. However, detection of the interface stress embedded in organic optoelectronic devices is a long-standing problem, which causes the unknown relationship between interface stress and organic device stability (one key and unsettled issue for practical applications). In this study, a kind of previously unknown molecular conformation-induced stress is revealed at the organic embedded interface through sum frequency generation (SFG) spectroscopy technique. This stress can be greater than 10 kcal/mol per nm and is sufficient to induce molecular disorder in the organic semiconductor layer (with energy below 8 kcal/mol per nm), finally causing instability of the organic transistor. This study not only reveals interface stress in organic devices but also correlates instability of organic devices with the interface stress for the first time, offering an effective solution for improving device stability.