CsPbBr3/p-Si membrane heterojunction photodiode: Photodetection characteristics and C-V analysis

We report the fabrication and physical characterization of a self-driven heterojunction photodetector based on an all-inorganic CsPbBr3 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 CsPbBr3 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 1.75×1011 Jones. Crucially, the strong built-in potential (Vbi = 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 (Dit ~ 1011 eV-1cm-2), confirming significant interfacial defect contributions to the non-ideal device behaviour. By employing a modified depletion approximation (MDA) incorporating the diode ideality factor (ν), we decouple parasitic trap-assisted processes from the intrinsic junction capacitance to resolve a precise Vbi 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.