Synthesis of Polyaniline/Sulfonated Polyaniline (PANI:SPAN) Acid–Base Pair Mimicking PEDOT:PSS Intermolecular Structure as a Hole-Transporting Layer

A conductive polymer made by in situ polymerization of polyaniline in sulfonated polyaniline (PANI:SPAN) was developed to emulate the acid–base interaction framework of PEDOT:PSS. The polymer is proposed as a low-cost alternative to both PEDOT:PSS and PANI:PSS for application as a hole-transport layer (HTL) in optoelectronic devices. Sulfonation of the emeraldine salt form of PANI (PANI-ES) was carried out using chlorosulfonic acid in chloroform, with 20 wt % yielding optimal substitution. Subsequent in situ polymerization in the presence of SPAN produced a green, water- and solvent-soluble PANI:SPAN powder. Acid–base interactions within the polymer were confirmed by vibrational spectroscopy. Conductivity measurements indicate that PANI:SPAN exhibits a sufficient electrical conductivity for HTL operation. UV photoelectron spectroscopy (UPS) analysis further reveals that the work function of PANI:SPAN closely matches that of PANI-ES. This alignment ensures effective hole extraction and transport, supporting its functionality as a charge-selective layer. The HTL properties of PANI:SPAN were evaluated through electrical measurements and compared to those of PEDOT:PSS. The Schottky barrier height at the PANI:SPAN/n-cSi interface was 0.747 eV, slightly lower than the PEDOT:PSS/n-cSi value of 0.769 eV, indicating improved hole injection. The rectification ratio (RR) of the PANI:SPAN/n-cSi device also exceeded that of the PEDOT:PSS counterpart, confirming the enhanced diode performance. These findings highlight the potential of PANI:SPAN as a processable and stable HTL material with favorable surface energetics and electronic characteristics. This study provides insight into acid–base polymer interactions and presents a viable alternative for next-generation conductive polymers in optoelectronic interface engineering.