Interface-Driven Performance Enhancement in Perovskite Solar Cells Using Oxygen-Tuned Cu-Doped NiOx Hole Transport Layer

Abstract

This work presents detailed investigation of defect chemistry and interface quality-driven performance enhancement of oxygen-tuned Cu-doped NiO hole transport layer (HTL) for perovskite solar cell (PSC). The results revealed that an increase in oxygen partial pressure activated dramatic variations in stoichiometry and electrical properties of Cu-doped NiO. The HTL layer prepared at 20% PO₂ during the growth showed the highest conductivity with a value of 12.9 S/cm, while the 10% PO₂ HTL exhibited the highest fraction of Ni³⁺ (0.76). Energy band alignment of HTL with perovskite layer demonstrated a minimal valence band offset of 0.13 eV for 20% PO2, which favors the efficient hole transfer between the two layers. Controlled oxygen partial pressure in HTLs reduces defect density from a peak of 3.01 × 10¹¹ cm⁻³ at 10% PO₂ to 1.71 × 10¹¹ cm⁻³ at 20% PO₂ and led to a twofold enhancement in the charge extraction rate. Finally, PSC based on the optimum HTL significantly boosts the efficiency with the power conversion efficiency reaching to 13.7% while reducing hysteresis to 4.5% from 7.60% in the controlled sample. This work links O₂ partial pressure-controlled defect chemistry and Ni³⁺/Ni²⁺ ratio in inorganic HTLs to interfacial band alignment and device performance.