We report a significant enhancement of the electron injection from n-Si bottom cathodes to organics by using a thin layer
of Cs2CO3 as electron injection layer, leading to the reduction of the turn-on voltages and the improvement of the
efficiencies in Alq3 based inverted top-emitting OLEDs with n-Si directly as cathodes. With structure of n-Si/ Cs2CO3 (2
nm)/TPBi (10 nm)/ Alq3 (40 nm)/ NPB (40 nm)/ MoO3 (2 nm)/Ag (20 nm)/ Alq3 (40 nm), where the 10 nm TPBi is hole
blocking layer for improving charge balance in emission zone and the 40 nm Alq3 layer on Ag anode is the capping layer
for improving light out-coupling efficiency, the inverted top-emitting OLEDs show a turn on voltage of 6 V and a
driving voltage of 10 V for 100 cd/m2 with a maximum efficiency of around 1.5 cd/A, which are superior compared to
the relevant results ever reported.
We report improved efficiency in Alq based top-emitting OLEDs with p-Si anode by using an effective electron injection layer and a hole blocking layer to realize better charge balance and recombination. With structure of p-Si/SiO2/MoO3 (2 nm)/NPB (40 nm)/Alq (40 nm)/TPBI (10 nm)/Cs2CO3 (2 nm)/Ag (20 nm)/Alq (40 nm), where the 40 nm Alq capping layer on top Ag cathode was used to improve out-coupling efficiency, the devices show a turn on voltage of 5.5 V and a driving voltage of 10 V for 100 cd/m2 with a maximum efficiency of exceeding 1.2 cd/A and a maximum power efficiency of 0.4 lm/W, which are comparable with the conventional OLEDs and encouraging and promising for Si based OLEDs and optoelectronics.
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