The Influence of Precursor Concentration on the Hole Transport Layer of Nickel-Oxide Thin Films Prepared by Sol-Gel Method

Abstract

This study systematically investigates the impact of precursor solution concentrations (8, 12, 16, and 20 mg/ml) on the structural and functional properties of sol-gel-derived nickel oxide (NiOx) hole transport layers () and their application in all-inorganic CsPbIBr₂ perovskite solar cells (PSCs). The NiOx films were characterized via XRD, SEM, contact angle measurements, and UV-Vis spectroscopy to evaluate crystallinity, morphology, wettability, and optical properties. Results reveal that the precursor concentration critically influences film quality: at 16 mg/ml, the NiOₓ HTL exhibits optimal crystallinity (cubic phase with (220) peak dominance), dense morphology, uniform surface energy distribution, and balanced optical-electrical performance. These attributes enhance charge transport, reduce interfacial defects, and promote CsPbIBr₂ crystal growth, minimizing pinhole defects in the perovskite layer. Photoluminescence (PL) and impedance spectroscopy further confirm superior hole extraction efficiency and reduced non-radiative recombination at 16 mg/ml. Consequently, PSCs incorporating this HTL achieve a maximum power conversion efficiency (PCE) of 4.42% (vs. 3.11% at 8 mg/ml), with improved short-circuit current density (9.76 mA/cm²) and fill factor (49.2%). This work provides critical insights into optimizing NiOₓ HTL fabrication for high-performance, cost-effective perovskite photovoltaics.

Keywords: NiOx HTL, all-inorganic CsPbIBr2 perovskite, sol-gel method, precursor concentration, photovoltaic performance