Electrochemically Engineered Lanthanum Nickelate as a Promising Transparent Hole-Transport Layer for Bulk Heterojunction Polymer Solar Cells: An Experimental and DFT Study

Lanthanum nickelate (LNO) was grown on an FTO-coated glass slide by employing the chronoamperometry method and used as a hole transport layer (HTL) in bulk heterojunction polymer solar cells (BHJ PSCs). The electrodeposition parameters, including the deposition time, potential magnitude, and electrolyte conditions, were changed to obtain LNO thin films, providing appropriate energy levels as an HTL. The electrochemical, morphological, optical, and structural characteristics of electrochemically produced LNO samples were compared to those of the sample prepared via the sol–gel procedure. The LNO sample prepared by applying −1.18 V while the electrolyte was stirring exhibited significantly better electrochemical and optical properties. The fabricated PSC using this sample provided a considerably higher (45.3%) power conversion efficiency (PCE) than the PSC prepared based on an LNO thin film acquired by the sol–gel method. The superior performance of the BHJ PSC was ascribed to the increased electroactive surface area (1.341 cm2), improved charge mobility (2.30 × 10–6 cm2 V–1 s–1), and reduced charge recombination probabilities. A short circuit current of 13.24 mA cm2, an open circuit voltage of approximately 0.64 V, a fill factor of 70%, an external quantum efficiency of 75.3%, and a PCE of 5.9% were demonstrated by the best fabricated PSC, surpassing the reference device with a PEDOT:PSS HTL. Moreover, the prepared PSC exhibited remarkable ambient stability, maintaining 84% of its initial PCE after 450 h of aging. The agreement between DFT calculations and experimental results confirmed that LNO possesses the optical and elastic characteristics required to improve the efficiency and stability of PSCs as an HTL.