Comparative studies on fluorescent emission of organic semiconductors between optical and electrical pumping*

Light-emitting devices of organic semiconductors (OSCs), such as organic light-emitting diodes, have widely been used in daily life. Especially, light-emitting organic field effect transistors (LE-OFETs) are considered as candidates for efficient light-emitting devices, such as OSC lasers, in the future. However, the detailed understanding of electroluminescence (EL) by electrical pumping has not fully been understood when it is compared to photoluminescence (PL) by optical excitations. For realizing such a highly performed light-emitting device, the fundamental understanding on the difference between EL and PL is necessary. Here, we report accurate comparative studies on the difference between PL and EL of 5,5’’-Bis(4-biphenylyl)-2,2’:5’,2’’-terthiophene (BP3T). The result shows that the spectrum shapes are different between PL- and EL- mode in the case of single-crystal thin films of BP3T and quenching of fluorescent emissions occurs in high current region in the EL-mode. In order to realize highly efficient light-emitting OFETs towards OSC lasers in the future, such annihilation would become a significant obstacle.