We proposed a simple yet robust film treatment method with methanol having only one hydroxyl group to enhance the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by four orders of magnitude. Different methods of film treatment: immersing PEDOT:PSS film in the methanol solution; dropping methanol on the film; and a combination of these are employed and the results are compared. The conductivity of PEDOT:PSS films was enhanced from 0.3 S cm⁻¹ to 1362 S cm⁻¹ after film treatment with methanol. Other alcohols like ethanol and propanol were also used to treat the PEDOT:PSS film and showed inferior conductivity enhancement compared to methanol. The conductivity enhancement was greatly affected by the hydrophilicity and dielectric constant of the alcohols used. The mechanism of conductivity enhancement was investigated through various characterization techniques including FTIR, XPS and AFM. Removal of the insulator PSS from the film, and morphology and conformational changes are the mechanisms for the conductivity enhancement. The treated films also showed high transmittance and low sheet resistance desirable for a standalone electrode. ITO-free polymer solar cells were fabricated using PEDOT:PSS electrodes treated with methanol and showed almost equal performance to ITO electrodes.

Considerable interest is raised by organic materials owing to their exceptional performance in electronic and optoelectronic applications. Among these, electrochromic materials (EC) that can be switched between a distinct color and a bleached state exhibiting high contrast, multicolor and improved long-term stability are attractive in the fabrication of electrochromic devices (ECDs). Ionic materials, in particular, have received persistent attention owing to their tunable optical and electronic properties. 4,4′-Bipyridinium salts, commonly called viologens (V²⁺), are a well-recognized class of electrochromic materials that exhibit three reversible redox states, namely, V²⁺ (dication, pale yellow colored/colorless) ↔ V⁺˙ (radical cation, violet/blue/green) ↔ V⁰ (neutral, colorless). The electrochromic properties of these materials can be modulated by varying the nitrogen substituents on the pyridyl ‘N’; also, besides this, varying the counter ions with specific functionalities has been shown to enhance the electrochromic behavior, such as switching time, cycling stability and device performance. Although ECDs based on viologens are well regarded for their low operational voltages, they exhibit certain disadvantages such as low cycle life and poor efficiency of the device in the long term. Extensive efforts have been made to fine tune the EC properties of viologens, either through alteration or by adding suitable electrochromic counter electrode materials, which includes the incorporation of conducting polymers in the device set-up and/or the addition of complementary redox species. Optimization of the device parameters has shown that the addition of such external agents has a positive effect on the overall device performance. This review describes recent developments in the synthesis of viologen-based electrochromes with co-redox species and their ECD performance.