Interface Engineering with Hole Collecting Carbazole Phosphonic Acid (PACz)‐ Self‐Assembled Monolayer: Investigation of Optoelectronic Behavior in Organic Solar Cell

Understanding the device physics of organic solar cell (OSC) requires examining interfacial layers, namely the hole and electron selective layer (HSL and ESL), which improves the performance of OSC by modulating electrical parameters. In this report, we evaluate the family of PACz molecules (2PACz, Br‐2PACz, MeO‐2PACz, and Me‐4PACz) as self‐assembled monolayers (SAMs) conjugated with bulk‐heterojunction (BHJ) OSCs for a sustainable HSL, directly functionalized onto indium tin oxide (ITO) anode. OSCs using PTB7‐Th:PC 71 BM BHJ and ITO/SAMs as anode achieve power conversion efficiency (PCE) of 7.75%. Further, to investigate the versatility of SAMs in OSCs, ITO/SAM anodes are combined with high‐performing photoactive materials (PM6:Y7), resulting in a PCE of 10.84%. The Br‐2PACz‐based OSC outperforms its alternatives due to its higher work function (WF: 5.61 eV) that enhances hole extraction, reduces interfacial resistance, and charge‐carrier recombination while blocking electrons. We attribute improved OSC performance to reduced contact resistance, bimolecular recombination losses, and optimized charge transport inside the BHJ. We assess surface morphology, WF, and optical properties of ITO/SAMs using atomic force microscopy, UV–Vis spectroscopy, and ellipsometry. Further, the electrical properties and charge‐carrier mobility of OSC devices are analyzed using impedance spectroscopy, space‐charge‐limited current, and transient photovoltaic analysis.