Poly(3,4‐Ethylenedioxythiophene): Methylnaphthalene Sulfonate Formaldehyde Condensate: The Effect of Work Function and Structural Homogeneity on Hole Injection/Extraction Properties

Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is widely used as hole injection/extraction material in organic optoelectronics. However, there still exist drawbacks for PEDOT:PSS such as low work function (WF), poor structural and electrical homogeneity. To solve these problems, methylnaphthalene sulfonate formaldehyde condensate (MNSF) is applied, which has excellent dispersion property, branched chemical structure, and low cost, as dispersant and dopant instead of linear PSS to prepare PEDOT:MNSF. The hole injection/extraction capability of PEDOT:MNSF is systematically studied in organic optoelectronic devices. PEDOT:MNSF‐1:6 exhibits unexpected high device performance with a maxima current efficiency of 33.4 cd A−1 in blue phosphorescent organic light‐emitting diode and a power conversion efficiency of 13.1% in CH3NH3PbIxCl3−x‐based inverted perovskite solar cell, respectively. Compared with PEDOT:PSS, the relatively higher efficiency of PEDOT:MNSF‐1:6 is attributed mainly to its higher WF of 5.29 eV, structural and electrical homogeneity. Our research displays a promising future of MNSF as a cheap and widely available alternative of PSS. Moreover, a clear map is provided for the design of dopant for PEDOT considering the structure of dopant. Comparing with poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), methylnaphthalene sulfonate formaldehyde condensate‐doped PEDOT with higher work function, excellent homogeneity, but low conductivity exhibits higher hole injection/extraction capabilities in organic light‐emitting diodes/perovskite solar cells. The semiconductivity of dopant and structural homogeneity are both key factors. The results demonstrate a panoramic prospect for the future design of dopant for PEDOT.