Electrochemical synthesis of Cu-doped nickel oxide thin film on indium tin oxide as hole transport layer in polymer solar cells

Cu-doped NiO nanostructures were electrochemically synthesized on indium tin oxide (ITO)-coated glass using cyclic voltammetry (CV) method and employed as the hole transport layer (HTL) in bulk heterojunction polymer solar cells (BHJ PSCs). In order to modify NiO nanostructures and adjust bandgap, Cu 2+ ions were electrochemically doped into the NiO nanostructure at various molar ratios, ranging from 1 to 5 %. The structural, optical, and electrochemical properties were systematically analyzed via electrochemical impedance spectroscopy (EIS), photoluminescence (PL), and CV techniques. The optimized NiO nanostructure, doped with 3 % Cu, exhibited significantly enhanced properties, including a suitable bandgap of approximately 3.38 eV, high conductivity (0.04 mS cm −1 ), increased electroactive surface area (1.430 cm 2 ), and improved charge mobility (1.36 cm 2 V −1 s −1 ). Polymer solar cells fabricated using the optimized 3 % Cu-doped NiO HTL demonstrated superior photovoltaic performance, achieving a power conversion efficiency (PCE) of 4.83 %, an open-circuit voltage (V OC ) of 0.64 V, a short-circuit current density (J SC ) of 10.55 mA cm −2 , and a fill factor (FF) of 65.45 %. Compared to pristine NiO-based PSCs, the efficiency of devices employing 3 % Cu-doped NiO increased by approximately 63.7 % in terms of PCE and 15.3 % in fill factor. Furthermore, the optimized device performance exceeded that of conventional PSCs employing PEDOT:PSS as HTL by approximately 66.6 %, highlighting Cu-doped NiO as a promising alternative for efficient polymer photovoltaic applications.