CsPbBr ₃ /p-Si membrane heterojunction photodiode: photodetection characteristics and C – V analysis

Abstract We report the fabrication and physical characterization of a self-driven heterojunction photodetector based on an all-inorganic CsPbBr ₃ thin film interfaced with a lightweight, freestanding p-type single-crystal silicon membrane (p-Si). Different from conventional rigid substrates, this membrane-based architecture leverages the superior carrier mobility and mechanical resilience of monocrystalline silicon for flexible, high-sensitivity optoelectronics. Beyond standard characterization, an Elliott-type quantum well model was employed to resolve the excitonic nature of the CsPbBr ₃ nanocrystals, revealing a significant exciton binding energy of 340 meV and a quasi-particle bandgap of 2.91 eV. Under zero-bias conditions, the device exhibits a robust broadband response with a peak responsivity of 0.1 A/W and a detectivity of 1.75 × 10 ¹¹ Jones. Crucially, the strong built-in potential ( V _bi = 0.91 V) facilitates efficient exciton dissociation, overcoming Coulombic attraction even at zero bias to enable high-performance self-powered operation. To elucidate the underlying transport physics, we conduct an in-depth study of the frequency-dispersive capacitance–voltage ( C – V ) characteristics. Our study reveals how interface states and deep-level defects dictate the steady-state photocurrent and transient kinetics (∼130 ms). C – V analysis further enabled the quantification of the interface trap density ( D _it ∼ 10 ¹¹ eV ⁻¹ cm ⁻² ), confirming significant interfacial defect contributions to the non-ideal device behavior. By employing a modified depletion approximation incorporating the diode ideality factor ( η ), we decouple parasitic trap-assisted processes from the intrinsic junction capacitance to resolve a precise V _bi of 0.91 V. This rigorous analytical approach provides critical insights into the non-ideal junction physics governing the performance of self-powered, membrane-based perovskite optoelectronics.