Role of MoO3-modified organic photovoltaic-type charge generation layer in tandem organic light-emitting diodes

- Role of each part in C60/CuPc/MoO3 charge generation layer (CGL) was studied.
- Charge generation mainly occurs at MoO3/NPB not C60-CuPc interface upon biases.
- C60-CuPc heterojunction shows excellent charge generation in the presence of light.
- Charges are also generated at CuPc/MoO3 interface at relatively high electric field.
- The results agree well with properties of tandem OLEDs with various MoO3-based CGLs.

The role of each part in MoO3-modified organic photovoltaic (OPV)-type charge generation layer (CGL) was investigated by incorporation into hole-only devices. The OPV heterojunction (HJ) consists of fullerene (C60) and copper phthalocyanine (CuPc). According to the electrical characteristics of hole-only devices, it was found that charge generation mainly took place at the interface between MoO3 and hole transport layer rather than the interface of C60-CuPc HJ under an electric field. The C60-CuPc HJ exhibited good charge generation in the presence of photons due to photovoltaic effect, despite its poorer charge generation upon an application of electric field. In addition, charges can be also generated at CuPc/MoO3 interface upon a relatively high electric field since the absorption band of charge transfer complex formed by CuPc and MoO3 is within visible region. These results, which had been rarely reported in the previous studies on OPV-type CGL, can well explain the experimental results of tandem organic light-emitting diodes (OLEDs) with MoO3 modified OPV-type CGLs.

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