Determination of the Thin-Film Structure of Zwitterion-Doped Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate): A Neutron Reflectivity Study

Abstract

Doping poly (3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is known to improve its conductivity, however little is known about the thin film structure of PEDOT:PSS when doped with an asymmetrically charged dopant. In this study, PEDOT:PSS was doped with different concentrations of the zwiterion 3-(N,N Dimethylmyristylammonio)propanesulfonate (DYMAP), and its effect on the bulk structure of the films characterized by neutron reflectivity. The results show that at low doping concentration, the film separates into a quasi bi-layer structure with lower roughness (10%), increased thickness (18%), and lower electrical conductivity compared to the undoped sample. However when the doping concentration increases the film forms into a homogeneous layer and experiences an enhanced conductivity by more than an order of magnitude, a 20% smoother surface, and a 60% thickness increase relative to the pristine sample. Atomic force microscopy and profilometry measurements confirmed these findings, and AFM height and phase images showed the gradually increasing presence of DYMAP on the film surface as a function of the concentration. Neutron reflectivity also showed that the quasi bi-layer structure of the lowest concentration doped PE-DOT:PSS is separated by a graded rather than a well defined interface. Our findings provide an understanding of the layer structure modification for doped PEDOT:PSS films that should be prove important for device applications.

Humidity‐Induced Nanoscale Restructuring in PEDOT:PSS and Cellulose Nanofibrils Reinforced Biobased Organic Electronics

“…For example, pure and differently doped PEDOT:PSS electrodes were recently studied with neutron reflectometry and a humidity induced swelling of the PEDOT:PSS films was observed. [5][6][7] The massive swelling of the organic electrodes can significantly affect related devices in applications.…”

Improved Performance and Stability of Organic Solar Cells by the Incorporation of a Block Copolymer Interfacial Layer

“…Figure a,d shows the 2D and 3D height images, respectively, of PEDOT:PSS which has an average root mean square roughness (RMS) of 1.49 ± 0.13 nm, a value that is consistent with literature. [ 45,82 ] Meanwhile, the 10 nm P3HT 50 ‐ b ‐PSS 16 (Figure 7b,e) and 13 nm P3HT 50 ‐ b ‐PSS 23 (Figure 7c,f) films have a very similar RMS of 0.49 ± 0.05 and 0.51 ± 0.05 nm, respectively, which is three times lower than that of PEDOT:PSS. The smoother surface of the block copolymers will allow the formation of an enhanced contact with the P3HT:PCBM layer improving the fill factor of the device.…”

“…Several efforts to improve the interface between PEDOT:PSS and P3HT have been made mainly by doping PEDOT:PSS with different substances in order to change its physical and chemical properties such as selective carrier blocking and mobility, PSS content, and morphology resulting in the improved performance and stability of the device. [ 41–44 ] However, since the morphological changes that PEDOT:PSS experiences after being doped are complex, [ 45 ] and to an extent not completely understood, this route toward improving the compatibility between PEDOT:PSS and P3HT:acceptor can be unreliable. Therefore, a different approach to improving the compatibility between PEDOT:PSS and P3HT:PCBM is adopted here.…”