N-Type doping in organic electronic devices

Abstract

A facile way to fabricate highly efficient organic light emitting devices (OLEDs) with insulator MnO as an electron injecting and transporting material was devised, which eliminates the problem of the oxidation of reactive dopants. The power efficiency of 1.1 lm/W by inserting 3-nm-thick MnO as the electron injecting layer was obtained, higher than the 0.8 lm/W efficiency for the reference device with 0.5-nm-thick LiF. A thermal co-evaporation layer containing 10% weight of MnO and tris(8-hydroxyquinolato)aluminum (Alq₃) as the electron transporting layer showed more efficient electron transport ability, with turn-on voltage of 3.8 V, lower than 7.4 V for the intrinsic Alq₃. Meanwhile, the insertion of thin MnO layer between organic photoactive layer and inorganic metal electrode significantly improved performance and stability of organic solar cell compared to device without it. The power conversion efficiency (PCE) of 2.91% by inserting 3-nm-thick MnO was obtained, higher than the 0.91% efficiency for the device without it, and 2.59% for the device with 0.5-nm-thick LiF. Charge transport of rhenium trioxide (ReO₃) in organic electronic devices was investigated. The hole injection/transport was blocked and the electron injection/transport was enhanced with doping of ReO₃ in organic electronic devices. Thus the charge balance and efficiency of the OLED were improved, 2.7 cd/A of current efficiency (CE) at 20 mA/cm² for the device with ReO₃ was higher than 1.5 cd/A for the device without it. In the case of organic photovoltaic cells (OPV), the open-circuit voltage (V_oc), 0.58 V, was higher compared to the device without ReO₃ (0.44 V) due to the improvement of interface properties. The PCE was increased to 2.27% by the combination of ReO₃ (increasing V_oc) with poly(3,4-ethylene dioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) (improve hole transport to increase J_sc) on the modification of the anode, higher than 1.85% for the device without ReO₃.