Impedance and Dielectric Relaxation Dynamics in AnE-PVad:PCBM Organic Solar Cell: Insights into Interfacial Polarization and Charge Transport

In this work, we investigated the dielectric behavior of an anthracene-containing poly-(<i>p</i>-arylene-ethynylene)-<i>alt</i>-poly-(<i>p</i>-arylene-vinylene) (AnE-PVad) copolymer blended with fullerene (PCBM). The study was carried out in an organic solar cell structure of ITO/PEDOT:PSS/AnE-PVad:PCBM/LiF/Al using impedance spectroscopy. The real part of the complex impedance (<i>Z</i>') reached high values at low frequencies. This behavior is consistent with space-charge accumulation and interfacial polarization caused by charge buildup in the bulk and at the electrode interfaces. At higher frequencies, dipoles aligned more effectively with the alternating field, which reduced the impedance. The Cole-Cole plots showed clear semicircular arcs that correspond to different relaxation processes and conduction mechanisms. These features were successfully interpreted using an equivalent circuit model. The dielectric constant (ε') displayed strong dispersion at low frequencies due to Maxwell-Wagner interfacial polarization. The dielectric loss (ε″) decreased sharply below approximately 10⁴ rad·s^-1, reflecting dipolar deformation and relaxation effects. Analysis of the complex electric modulus <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo> <mml:msup><mml:mi>M</mml:mi> <mml:mo>*</mml:mo></mml:msup> <mml:mo>=</mml:mo> <mml:msup><mml:mi>M</mml:mi> <mml:mo>'</mml:mo></mml:msup> <mml:mo>+</mml:mo> <mml:mi>j</mml:mi> <mml:msup><mml:mi>M</mml:mi> <mml:mo>″</mml:mo></mml:msup> <mml:mo>)</mml:mo></mml:math> offered further insight into charge-transport dynamics and space-charge relaxation within the active layer. The real part of the modulus (<i>M</i>') increased markedly with angular frequency, indicating a shift from electrode-dominated to bulk-controlled conduction. The impedance and dielectric analyses show that the electrical response of the AnE-PVad:PCBM solar cell is governed by interfacial polarization and field-dependent relaxation mechanisms. These findings provide a deeper understanding of charge dynamics in organic photovoltaic systems.