Methodology for Improved Adhesion for Deposited Fluorinated Transparent Conducting Oxide Films on a Substrate
Transparent conducting films (TCF) are typically used in various photovoltaic and display devices. Inorganic films typically consist of transition metal materials with a variety of compositions and doping to achieve a transparent conducting film, such as a transparent conductive oxide (TCO). In solar cell applications, the TCO may act as a transparent coating for light to pass through unimpeded to the active absorber material underneath the conducting oxide and/or as an ohmic contact for carrier transport out of a device incorporating the conducting oxide and/or as a barrier layer to keep out atmospheric contaminants (e.g., water, oxygen, dirt, etc.). Similarly, in display applications, TCOs act as a transparent top contact that allows the visible light to pass through it unimpeded out of the device and may also serve as a permeation barrier.
Fluorine doped metal oxides, such as fluorine doped tin oxide (FTO), are also used in the generation of TCOs. However, extreme operating conditions (>500 C) are necessary to generate transparent fluorine doped metal oxide films using existing current commercial manufacturing methods such as spray pyrolysis or chemical vapor deposition processes. These known commercial manufacturing methods when employed at standard atmospheric pressures tend to yield oxide films with rough and/or diffusive surface morphologies. This produces a great disadvantage to the resulting conducing oxides because the transmittance of these materials can be dramatically decreased by light scattering at defects and grain boundaries on the oxide film. Such defects can also limit the conductive performance of electrical devices such as semiconductor chips.
Achieving the high temperatures necessary for the deposition process such as spray pyrolysis or chemical vapor deposition requires a large amount of energy and can be expensive to maintain for long periods of time. Additionally, such elevated temperatures tend to cause damage to underlying layers and or substrate in or under the multilayer devices having a conducing oxide top layer. Fluorinated metal oxide films, like FTOs, can also be produced via sputter deposition at room temperature. However, commercial use of sputtered fluorinated metal oxides, like FTOs, is further limited because these particular fluorinated metal oxides tend to delaminate from a substrate surface. For these reasons the use of fluorine doped metal oxides as a top layer conductor for semiconductors, photovoltaic cells, and similar devices has been limited.Description
NREL scientists have developed a new method for magnetron sputter or atomic layer deposition of fluorinated metal oxides, specifically tin oxide. The process starts by first putting an ‘adhesion layer’ of 10-30 nm non-fluorinated oxide down, followed by a sputter deposition of the FTO improved by the addition of CF4 gas. The process results in films that have improved conductivity and do not delaminate from the substrate surface. This allows for sputter deposition of fluorinated metal oxides at greatly reduced temperatures with properties to those currently done by spray pyrolysis at >500 C.Benefits
- Lower temperature deposition
- Stronger forming adhesion of fluorinated metal oxides
- Screen Displays
- Field Effect Transistors (FETs)
- Micro-Electro-Mechanical Systems (MEMS) Devices
- Thin Layer Energy Devices
|Title and Abstract||
METHODOLOGY FOR IMPROVED ADHESION FOR DEPOSITED FLUORINATED TRANSPARENT CONDUCTING OXIDE FILMS ON A SUBSTRATE
A method and device for improving the adhesion of fluorinated transparent conducting oxide films by incorporating a non-conducting, non-fluorinated adhesion layer between a substrate and a transparent conducting oxide.
|National Renewable Energy Laboratory||11/14/2014
|Technology ID||Development Stage||Availability||Published||Last Updated|
|NREL ROI 12-76||Prototype||Available||03/06/2015||03/06/2015|