We report extremely high light out-coupling efficiency from a transparent organic light-emitting diode (OLED) integrated with microstructures on both sides of the device. The OLED having a metal free structure offers dramatically reduced surface plasmonic loss and absorption loss. To extract the confined light inside the device, a high refractive index light extraction pattern was directly fabricated on the top side transparent conducting oxide electrode using a simple evaporation method, and a micro lens array sheet was simultaneously attached on the bottom side of the glass substrate. As a result, the external quantum efficiency of the device increased from 18.2% to 47.3% by using the microstructures, and was additionally enhanced to 62.9% by attaching an index-matched hemisphere lens instead of the micro lens array on the glass side in order to reduce additional light guiding loss inside of the device. These values showed very good agreement with the simulation performed by a combination of the dipole model and a 3-dimensional geometrical simulation.
We reported a couple of methods to improve electron injection from the ITO electrode, thereby to fabricate efficient
inverted bottom emission organic light emitting diodes (IBOLEDs). The first method is to use an n-doped electron
transporting layer (ETL) as the electron injection layer. Electron only device characteristics and UPS measurements
confirmed that B3PYMPM homo-junction has the lowest injection barrier at the interface among three different ETLs,
resulting in the highest maximum EQE of 19.8% at low voltage in IBOLEDs. The energy barrier between n-ETL and
ETL is one of the most important factors for high performance inverted OLEDs. The second method is to use an organic
p-n junction as an electron injection layer, where the p-n junction generated electrons and holes under reverse bias,
which corresponds to the forward bias in the OLEDs. The organic p-n junction composed of a p-CuPc/n-Bphen layer
shows almost the same electron injection characteristics for the cathodes with different work functions whereas the
injection characteristics of the n-Bphen EIL significantly depend on the work function of the cathode. These facts
indicate that the organic p-n junction can be efficiently applied as an electron injection layer for high performance
flexible organic electronics, regardless of the electrodes.
High efficiency near-infrared (NIR) absorbing solar cells based on lead phthalocyanine (PbPc) are reported using copper
iodide (CuI) as a templating layer to control the crystal structure of PbPc. Devices with CuI inserted between the ITO
and PbPc layers exhibit a two times enhancement of the JSC compared to the case in the absence of the CuI layer. This is
due to the increase of crystallinity in the molecules grown on the CuI templating layer, which is investigated via an x-ray
diffraction study. Moreover, fill factor is also enhanced to 0.63 from 0.57 due to low series resistance although the
additional CuI layer is inserted between the ITO and the PbPc layer. As a result, the corrected power conversion
efficiency of 2.5% was obtained, which is the highest one reported up to now among the PbPc based solar cells.
We demonstrated that an organic p–n junction was successfully adapted to inverted organic light emitting diodes
(IOLEDs) as an electron injection layer (EIL). The organic p–n junction composed of a ReO3 doped copper
phthalocyanine (CuPc)/Rb2CO3 doped 4,7-diphenyl-1,10-phenanthroline (Bphen) layer showed very efficient
charge generation under a reverse bias reaching to 100 mA/cm2 at 0.3 V and efficient electron injection from
indium tin oxide (ITO) when adopted in IOLEDs. Moreover, the organic p–n junction resulted in the same
current density–voltage–luminance characteristics independent of the work function of the cathode, which is a
valuable advantage for flexible displays.