Organic–Inorganic PTB7-Th:ITIC/ZnO Heterojunction Based Self-Powered Photodetectors with Tunable Dual Detection Windows

In this work, we demonstrate a filter-free self-powered photodetector based on PTB7-Th:ITIC/ZnO heterojunction that exhibits remarkable selective spectral response characteristics. The device achieves band-selective detection through innovative manipulation of incident light direction, enabling multiple spectral detection capabilities within a single architecture. Under 0 V bias voltage operation, the device exhibits dual-mode detection capability depending on the illumination direction. When illuminated through the ZnO film side, the photodetector demonstrates visible light detection with a peak responsivity of 350 mA W^-1 across the 400-800 nm spectral range. Conversely, illumination through the bulk heterojunction film side enables broadband detection from ultraviolet to visible spectrum (300-800 nm), showing distinct responsivity peaks at 2 mA W^-1 and 29 mA W^-1 for ultraviolet and visible regions, respectively. The selective spectral response characteristics of the PTB7-Th:ITIC/ZnO photodetector are primarily governed by two key factors: the optimized width of the depletion layer region and the distinctive distribution profile of the internal electric field. This work establishes a paradigm for developing autonomous photodetection systems capable of adaptive spectral discrimination, paving the way for advanced optoelectronic applications in complex environmental conditions.