Dual functions of light-emission and light-harvesting using organic donor and acceptor co-deposition

Abstract

The device working principles of light emission and light harvesting using p-n (or donor-acceptor) heterostructures are reciprocal relations in terms of thermodynamics and charge transfer mechanisms. The dual-functional optoelectronic systems of organic light-emitting diodes (OLEDs) and organic photovoltaic cells (OPVCs) including organic photodiodes (OPDs) were obtained by fabricating the devices with bi-layer (BL) and triple-layer (TL) structures through the co-deposition of p-type rubrene and n-type NDI-C6 molecules using organic molecular beam deposition. The concentration ratio of rubrene:NDI-C6 for the co-deposition layers (CDLs) was controlled by deposition rates of 3:7, 5:5, and 7:3, resulting in the distinctive performance of the devices. The OLEDs with rubrene/CDL 3:7/NDI-C6 TL structures show considerably broad and enhanced electroluminescence emission by approximately 40 times including a drastic increase in the exciplex EL peak at 695 nm, compared to those of the OLEDs with rubrene/NDI-C6 BLs or other TL structures. As the concentration of n-type NDI-C6 in the CDL increased, the driving voltage decreased, and the current increased for the OLED with the TL structure. The fill factor and power conversion efficiency of the OPVCs and photodetectivity using the same devices increased with increasing concentration of n-type NDI-C6. The dual performance of the OLED and OPVC, including the OPD of the elaborated co-deposition of organic molecules, was clearly observed, even though the efficiencies of the devices were relatively low. In our optoelectronic devices, the optimal concentration ratio of p-type rubrene and n-type NDI-C6 of the CDL in the TL devices was 3:7 for the dual function of light emission and light harvesting.