Low-cost Flexible Transparent Electrodes based on Amorphous Ag–ZTOF (Zn–Sn–O–F) Composites
Hazen Research, Inc., in collaboration with the National Renewable Energy Laboratory (NREL), developed a new class of amorphous transparent conductive electrodes (TCEs). The TCEs are based on zinc tin oxyfluoride–silver nanowire (ZTOF–AgNW) and zinc tin oxyfluoride–silver nanowire–zinc oxide (ZTOF–AgNW–ZnO) composites. The ZTOF bottom layer is amorphous and showed a columnar thin film growth mode. ZTOF is a wide bandgap semiconductor (Eg approximately 3.6 eV) and is a solid solution of ZnF2 with high optical transmittance and SnO2 with high refractive index. ZTOF is expected to improve internal light extraction and could serve as an internal light extraction layer (IEL) to improve the organic light-emitting diode (OLED) efficiency. The intermediate AgNW layer provides high conductivity, and the top ZnO layer protects the AgNW from degradation. Three types of TCE films were deposited on Corning Eagle XG glass substrates by spin-coating at process temperatures below 325°C: ZTOF onlyZTOF–AgNW ZTOF–AgNW–ZnO Thin film TCEs with a total thickness of approximately 250 nm were grown using a low-cost, nonvacuum, low-temperature, metal–organic deposition method. More than 100 thin film TCE samples were deposited and processed by Hazen, and more than 25 TCE samples were characterized by NREL. The ZTOF thin films showed about 95% transmittance (T), 10 nm root mean square (RMS) surface roughness, and very high sheet resistance (Rs). ZTOF–AgNW films had an Rs of about 15 ohms/sq, a T of 80%, and an RMS surface roughness of 50–75 nm. The ZTOF–AgNW–ZnO films had an Rs of 15 ohms/sq, a T of 80%, and an RMS surface roughness of approximately 20 nm. The OLEDs fabricated using ZTOF–AgNW composite TCEs (under the solid-state lighting testing program at OLEDWorks) did not produce a functional device. We believe the high RMS surface roughness of the ZTOF–AgNW (approximately 50–75 nm) could have resulted in a discontinuous cathode organic layer (approximately 100 nm). The plan to continue the OLED testing using a smoother ZTOF–AgNW–ZnO composite is under review. This new class of composite TCEs has the potential to be a combined IEL–TCE for OLEDs as ink jet printable patterns. Through further development and demonstration, these new TCEs are expected to meet the solid-state lighting program’s technical, performance, and cost targets set by the US Department of Energy (DOE). Potentially, the TCEs can be mass produced and commercialized as low-cost, efficient, and large-area OLED light sources.
- Research Organization:
- Hazen Research
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Science (SC)
- Contributing Organization:
- National Renewable Energy Laboratory (NREL)
- DOE Contract Number:
- SC0018834
- OSTI ID:
- 1524220
- Type / Phase:
- STTR (Phase I)
- Report Number(s):
- 12569-Hazen-NREL Project Report; 3032794501
- Country of Publication:
- United States
- Language:
- English
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