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

Abstract

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 cm 2 ), improved charge mobility (2.30 × 10 −6 cm 2 V −1 s −1 ), and reduced charge recombination probabilities. A short circuit current of 13.24 mA cm 2 , 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.

In Situ Electrochemical Cobalt Doping in Perovskite-Structured Lanthanum Nickelate Thin Film Toward Energy Conversion Enhancement of Polymer Solar Cells

“…The reference and counter electrodes were left unchanged. This step, consistent with prior research, aimed to eliminate any interference from the FTO substrate, thereby making it possible to produce a pure diffraction pattern of the LNO film to compare the samples easily …”

“…An energy difference between the valence band’s upper edge, mainly influenced by the O 2p band, and the conduction band’s lower end, primarily derived from the Ni 3d band, is described as the optical band gap ( E g ) . The UV–vis spectra of the produced materials were employed in combination with Tauc plot approach to determine the E g .…”

“…Following that, the slides were ready to be used as working electrodes. To generate the appropriate thin layer of the synthesized samples, the ED was performed by providing −1.18 V to the FTO electrode versus the Ag/AgCl reference electrode for 2 min at room temperature . Following washing with DI water, the samples were placed in an oven to undergo annealing for 5 h at the maximum temperature of 600 °C that FTO can withstand.…”

“…This process offers several distinct advantages over the above-mentioned traditional synthesis methods. First, electrochemical doping enables precise control over dopant concentrations and spatial distribution, facilitating the engineering of desired electronic properties . Second, it is a relatively simple and scalable process, compatible with a wide range of substrates and complex geometries .…”

“…Polymer solar cells (PSCs) are a highly promising energy conversion technology that possesses several outstanding features, such as lightweight, cost-effectiveness, solution processability, mechanical flexibility, and ease of fabrication for large-scale devices . The active layer (AL), electron transport layer (ETL), hole transport layer (HTL), and device interfaces are crucial components that determine the efficiency, stability, and performance of PSCs . These critical issues urgently require improvement since PSCs cannot be successfully commercialized unless they tolerate heat, light, and moisture.…”