Highly Transparent BiEDOT‐Based Conducting Polymers as Tailorable Hole Transport Materials for Perovskite Solar Cells

The development of new transparent conducting polymers is critical for advancing next‐generation optoelectronic technologies. Here, we introduce a new class of highly transparent BiEDOT‐based conducting polymers as an alternative to PEDOT:PSS, obtained via in situ oxidative polymerization of the BiEDOT dimer within a polymethylmethacrylate (PMMA) matrix using Cu(ClO 4 ) 2 . This interpenetrating polymer network (PBiEDOT‐PMMA) combines the high conductivity of PBiEDOT with the excellent film‐forming ability and chemical robustness of PMMA, yielding uniform, pinhole‐free films with tunable conductivity and superior optical transparency across the visible and near‐infrared regions. When used as a hole transport material (HTM) in inverted perovskite solar cells, PBiEDOT‐PMMA delivers a marked enhancement in open‐circuit voltage (V oc ) compared to PEDOT:PSS. Ultraviolet photoelectron spectroscopy (UPS) reveals a more favorable energy‐level alignment between the perovskite valence band and PBiEDOT‐PMMA than with PEDOT:PSS, which directly facilitates more efficient hole extraction and reduces interfacial energy barriers. The enhancement of V oc is the most direct fingerprint of the superior interfacial quality achieved with PBiEDOT‐PMMA, underscoring its potential as a robust alternative to PEDOT:PSS for high‐efficiency perovskite solar cells. Complementary analyses (PL, TRPL, quasi‐Fermi level splitting, ideality factor, and impedance spectroscopy) consistently confirm reduced recombination losses. Beyond photovoltaics, the simplicity, scalability, and cost‐effectiveness of this synthetic strategy, together with the ability to formulate processable inks, make PBiEDOT‐PMMA a promising candidate for a wide range of optoelectronic applications, including flexible electronics, OLEDs, sensors, and transparent conductive coatings.