Thermally Fine-Tuned NiO _x –MAPbI ₃ Interfaces for High-Sensitivity Self-Powered Photodetectors

Self-powered perovskite photodiodes offer the potential for low-cost, scalable manufacturing, yet achieving reliable, high performance still requires careful optimization of the interfaces between the perovskite absorber and charge-transport layers. Here, we examine how the postdeposition annealing temperature affects the structural and optoelectronic properties of sol–gel-derived nickel oxide (NiO x ) hole-transport layers (HTLs) for methylammonium lead iodide (MAPbI 3 ) self-powered photodiodes. NiO x films were annealed at 300, 350, and 400 °C and the resulting effects on device performance capabilities were systematically evaluated. Surface and interfacial analyses show that the NiO x HTL annealed at 300 °C exhibits a homogeneous morphology, an increased fraction of Ni 3+ species, and a deeper valence-band maximum, together yielding more favorable energy-level alignment with MAPbI 3 . MAPbI 3 layers grown on this optimized surface have larger grains, facilitating efficient photogeneration and charge extraction. Devices using the NiO x HTL annealed at 300 °C deliver the highest power conversion efficiency (∼17.3%), driven by higher short-circuit current density and fill factor values, while maintaining an open-circuit voltage. Photodetector metrics corroborate this advantage, with the spectral responsivity R λ ≈ 426 mA/W at 640 nm, noise-limited detectivity D * ≈ 2.53 × 10 12 Jones, shot-noise-limited detectivity D shot * ≈ 1.60 × 10 14 Jones, and a linear dynamic range ≈187 dB, together with sub-70 μs temporal responses and clear signal retention under ultralow illumination (∼190 pW). These results collectively demonstrate that a NiO x –MAPbI 3 interface thermally engineered at 300 °C is essential for achieving scalable, self-powered photodiodes with fast response times, low noise, and high sensitivity, delivering consistently superior performance across diverse illumination levels.