Why Organic Electronic Devices Comprising PEDOT:PSS Electrodes Should be Fabricated on Metal Free Substrates

Abstract

Poly(3,:polystyrene sulfonate (PEDOT:PSS) is up to date the most popular and commercially most successful conductive polymer. It is being used not only for antistatic, anticorrosion, and even antifouling coatings on one hand, but also, owing to its plasma frequency residing within the far-infrared region, for semi-transparent electrodes or charge extraction layers in solar cells on the other hand. The work function of an electrode plays an important role in the performance of any electronic device. Therefore, proper tuning of electrode work functions in semiconductor devices is crucial. It is worth mentioning that the work function of electrodes can be impacted by uncontrolled conditions during film processing because even monomolecular adsorbates may cause noticeable changes. Due to its ionic properties governed by the sulfonate group and its counterion, PEDOT:PSS is strongly hygroscopic, which may influence its functionality. Furthermore, the acidity of the same may lead to the release of additional ions from the neighboring layer. In this contribution, the work function of PEDOT:PSS films, cast from various commercial formulations, was monitored in dependence of the impact of (a) post-production thermal annealing and (b) storage under wellcontrolled relative humidity conditions for (c) certain durations. Indeed, work functions could be correlated with the surface concentration of metal ions, which clearly depended on the mentioned processing conditions. Finally, the impact of processing conditions on the performance of organic solar cells was demonstrated.

Optimized Stoichiometry for CuCrO2 Thin Films as Hole Transparent Layer in PBDD4T-2F:PC70BM Organic Solar Cells

“…This polymeric material has been selected due to its solubility in water [ 5 ], which allows its synthesis through solution-based processes, and to its high transparency, around 90%. However, this polymer presents several disadvantages such as heterogeneous electrical properties [ 6 ], inefficient electron blocking function as proved by results from polymer light-emitting devices [ 7 ], with a Lowest Unoccupied Molecular Orbital (LUMO) at 3.5 eV [ 8 , 9 ] and a Highest Occupied Molecular Orbital (HOMO) around 5.2 eV [ 10 , 11 , 12 ]. This polymer is also characterized by a strong acidity, which promotes the corrosion of the Indium Tin Oxide (ITO) layer used as transparent electrode [ 13 , 14 , 15 ].…”

Introduction of a Novel Figure of Merit for the Assessment of Transparent Conductive Electrodes in Photovoltaics: Exact and Approximate Form

“…PEDOT:PSS consists of a conductive part, the conjugated polymer PEDOT, and an insulating polyelectrolyte PSS that encapsulates the former. [ 46 ] PSS is generally used in formulations to bring PEDOT into an aqueous processable form. While as‐prepared PEDOT:PSS films have low conductivity, doping or post‐processing treatments with solvents, surfactants, salts, etc., have shown to increase the conductivity of PEDOT:PSS films.…”

“…While as‐prepared PEDOT:PSS films have low conductivity, doping or post‐processing treatments with solvents, surfactants, salts, etc., have shown to increase the conductivity of PEDOT:PSS films. [ 46 ] For example, dimethyl sulfoxide (DMSO) is a commonly used polar solvent for inducing enhanced phase separation between PEDOT and PSS. This leads to increased interactions between individual PEDOT chains and decreases the interaction with the PSS segments, which yields an overall improved phase connectivity of the charge conducting PEDOT.…”

Improved Hole Extraction Selectivity of Polymer Solar Cells by Combining PEDOT:PSS with WO3

“…On the one hand, PEDOT:PSS has the advantage of being solution processable at room temperature, but on the other hand, this material is also known to contribute to device degradation by unwanted reactions with the photoactive material and indium tin oxide (ITO) anode in the conventional architecture. [ 5–10 ] Alternatively to PEDOT:PSS, several solution‐processable metal oxides (NiO x , MoO x , and WO 3 ) have been introduced, either directly as crystalline nanoparticles or derived from sol–gel processes. [ 11–14 ] They combine the advantages of simple synthesis, high optical transparency, and good environmental stability.…”