PEDOT:PSS (or Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) is a transparent conductive polymer. It is a mixture of the ionomer poly(3,4-ethylenedioxythiophene), carrying positive charges, and polystyrene sulfonate, carrying negative charges. Due to its unique combination of conductivity, transparency, ductility, and ease of processing, PEDOT:PSS has become a benchmark material in thin-film electronic fabrication. There are many types of PEDOT dispersions, including PEDOT:PSS AI 4083 and PEDOT:PSS PH 1000.
In organic light emitting diodes, organic photovoltaics, and perovskite photovoltaics, PEDOT:PSS can be used as an interfacial layer for hole transport. It can also be used as a replacement for transparent conductors such as ITO or FTO. Commonly, it is used in applications where the underlying substrate is flexible.
The properties of PEDOT:PSS vary between dispersions, hence its versatility. The key properties of PEDOT:PSS are its conductivity and the size of its work function. Since PEDOT is conductive and PSS is insulating, the conductivity of the resulting polymer depends on the ratio between the two ionomers and the microstructure of the film. Similarly, a higher presence of PSS at the surface will result in a deeper work function.
PEDOT:PSS is typically available as a water-based emulsion. It is created via the polymerization of PEDOT monomers in a polystyrene sulfonic acid solution.
PEDOT:PSS is the subject of a considerable amount of research and is used for a range of applications within thin-film electronic fabrication. This includes perovskite photovoltaics, organic photovoltaics, organic light emitting diodes, transparent conductors, organic electrochemical transistors, flexible electronics, thermoelectric generators, supercapacitors, and energy storage.
PEDOT:PSS has been used as a hole extraction material in inverted devices. This material facilitates the extraction of charge carriers at the interface between the transparent conductive oxide and the active perovskite layer. Inverted perovskite devices using PEDOT:PSS typically show lower hysteresis than standard architecture devices. In addition, recent work on standard architecture devices shows that the toluene-based PEDOT:PSS can be used as a cheap alternative to Spiro-OMeTAD.
PEDOT:PSS has long been used as a standard material in device fabrication. It has been extensively used with materials such as P3HT and PCDTBT to form the backbone of fundamental research into polymer solar cells. In addition, PEDOT:PSS is being used in combination with state-of-the-art organic photovoltaic materials to push new efficiency limits。
Organic Light Emitting Diodes：
The use of PEDOT:PSS in organic light emitting diodes, as a well-established standard hole injection material, has been widespread for over a decade. Recent work still uses PEDOT:PSS due to its deep work function. This allows for efficient charge injection into white emitting polymers as well as host materials for thermally activated delayed fluorescence materials.
PEDOT:PSS is a potential replacement for expensive transparent metal oxides, such as ITO and FTO. Its effectiveness in both organic photovoltaic and perovskite photovoltaic devices has been demonstrated. In addition, in combination with metallic grid structures, it is possible to achieve sheet resistances comparable to metallic films.
Substrate surfaces should be prepared before the deposition of PEDOT:PSS to ensure that they are clean. This can be done using deionised (DI) water, Hellmanex III, isopropyl alcohol and a UV ozone cleaner. Once the surface is ready, a PEDOT:PSS thin film can be formed using a spin coater.
To ensure a uniform coating, it is important that the surface of your substrate is as clean as possible before you begin the deposition process. To prepare a substrate for PEDOT:PSS deposition:
- Choose a substrate (FTO glass, ITO glass, or silicon) and place it in a substrate rack.
- Sonicate your substrate for 5 minutes in hot (70°C) DI water with 1% Hellmanex III.
- Dump-rinse twice in boiling DI water.
- Sonicate your substrate for 5 minutes in isopropyl alcohol.
- Dump-rinse twice in boiling DI water.
- Dry your substrate using filtered compressed gas.
- Place the substrate into a UV ozone cleaner and leave for 10 minutes.
Thin Film Deposition of PEDOT:PSS
For the deposition of thin films of PEDOT:PSS on a freshly prepared surface, we recommend using a vacuum-free spin coater and following this five-step process:
- Filter your PEDOT:PSS solution through a0.45 µm0.45 PES filter (or hydrophobic PTFE filter for HTL Solar 3) into an amber vial.
- Preheat a hot plate to 120 °C.
- Place your freshly prepared substrate into an Ossila Spin Coater and set to the desired spin speed.
- The substrates should be spun until the films are dry; for PEDOT:PSS films this is typically >30 seconds.
- Once the spin coating has finished, place the samples on a hotplate for 15 minutes to fully dry.
For speeds below 1000 rpm we recommend static spin coating. For higher speeds, dynamic spin coating can be used。
Obtaining a Uniform Coating
The coating quality of the PEDOT:PSS is dependent on several factors. These include the PEDOT formulation you are using, the deposition technique, the surface you are depositing onto, and the cleanliness of the surface. Ideally, the film should be highly uniform across the entire surface although variations at the ends of your sample can occur due to edge effects.
Due to the wetting conditions of the PEDOT formulation on the surface, the coating may not always be uniform. If this occurs there are several things that can be done. The first is to ensure that the surface of your sample is clean, if possible use a combination of solvent cleaning steps and UV ozone or oxygen plasma treatments to ensure a completely clean surface. If this does not improve the quality of the surface, secondary solvents can be added. For AI 4083 and PH 1000, the addition of approximately 10% isopropanol can improve the wetting on surfaces