Developing efficient small molecule-based organic photo-couplers by optimizing the cathode interfacial layer in the photodetector

An organic photo-coupler (OPC) is one of the optoelectronic devices that is packaged face-to-face with electrically isolated input and output components. Substantially, the performance of OPC depends on the detection capability of an organic photodetector (OPD) when irradiated by an organic light-emitting diode (OLED). When illuminated, a tandem OLED transmits light with a wavelength of 560 nm. Four different hole blocking layers (HBLs) in OPD structures, i.e., BPhen, 10 nm thick C-60, 20 nm thick C-60, and C-60:LiF, are investigated to achieve a low dark current density, high current transfer ratio (CTR), higher cut-off frequency, and fast photo-response pulse of the OPC. Overall, at an applied bias of -3 V, the small molecule-based OPC demonstrates the lowest dark current density (OPC D) down to the level of 3.642 x 10(-9) A cm(-2), CTR (OPC A) above 18%, a wide cut-off frequency in the range of 644 kHz (OPC A) <= f(-3dB) <= 708 kHz (OPC D), and a transient photo-response faster than 500 ns at a frequency of 600 kHz. The thorough electrical and optical characterization carried out in this study is expected to pave the way for developing optimized OPCs for practical applications.