On April 14, 2022, Nature Energy reported on the alcohol-dispersed conductive polymer formulation PEDOT by Professor Zhou Yinhua's group from Huazhong University of Science and Technology with the title "An alcohol-dispersed conducting polymer complex for fully printable organic solar cells with improved stability T:F , and realized a high-performance all-printed organic photovoltaic cell based on this formulation. The photo of the fabricated device was selected as the cover image of Nature Energy's April 2022.

The conductive polymer PEDOT:PSS has the advantages of electrical conductivity, optical transparency, and solution coating. Since its invention in 1990, it has been widely used in many fields such as solid capacitors, antistatic coatings, and printed electronics. In fully printed organic photovoltaic cells, PEDOT:PSS undertakes the task of hole collection, which plays a key role in device performance. However, PEDOT:PSS has disadvantages such as strong acidity, easy moisture absorption, and poor wettability on the surface of the active layer, which limit the efficiency and stability of all-printed organic photovoltaic cells.

In order to overcome these shortcomings, Zhou Yinhua's research group adopted a counter ion substitution strategy to develop an alcohol-dispersed conductive polymer formulation. They used perfluorosulfonic acid ionic polymer (PFSI) as a counter ion, the unique advantage of PFSI is that it has two solubility parameters (16.71–17.37cal^0.5cm^-1.5 and 9.61–10.08cal^0.5cm^-1.5), which can be found in Dissolved in water or alcohol, respectively. Based on this, they realized an alcohol-phase dispersed conductive polymer formulation (abbreviated as PEDOT:F). The surface tension of the alcohol solvent is small, and the ionization constant of the acid in the alcohol is small. Therefore, the alcohol phase formulation can effectively improve the processing wettability and inhibit the acidity of the formulation. In addition, the perfluorosulfonic acid structure has strong hydrophobicity, which avoids the problem of moisture absorption. The perfluorosulfonic acid structure improves the work function of PEDOT, which is beneficial to the collection of holes.

The study found that the alcohol phase PEDOT:F has excellent universality in organic photovoltaic cells, and can interact with various organic photovoltaic active layers (fullerene or non-fullerene acceptors, deep or shallow energy level donors) and different devices. structure (trans or formal structure) is compatible, efficient hole extraction, high fill factor and high open circuit voltage are achieved. Further, they realized fully printed organic photovoltaic cells and modules. The energy conversion efficiencies of the achieved cells and modules were 15% and 13%, respectively, and the cells showed good stability.

The silver nanowires used in the electrodes in the organic photovoltaic cells in this article are from XFNANO.

Literature link: https://doi.org/10.1038/s41560-022-00997-9