High-Efficiency Polariton Organic Photodetectors via Trap-Assisted Photomultiplication.

We report a high-performance photomultiplication-type organic photodetector (OPD) based on a poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene]:[6,6]-phenyl-C61-butyric acid methyl ester (MDMO-PPV:PC61BM) active layer operating in the ultrastrong coupling regime. Systematic optimization of the PC61BM ratio in reference non-cavity devices confirms that trap-assisted hole injection from the Ag contact enables external quantum efficiencies (EQEs) exceeding 2000% and fast transient responses under 521 nm illumination, close to the absorption peak of MDMO-PPV. Incorporation of the optimized PC61BM ratio into a λ/2 microcavity produces well-resolved lower (LP) and upper (UP) polariton branches with a pronounced Rabi splitting of approximately 0.9 eV, confirming the establishment of ultrastrong light-matter coupling. The resulting cavity OPD exhibits a distinct wavelength-dependent response compared with its non-cavity counterpart, achieving maximum EQEs of 838% at 450 nm (near the UP mode) and 445% at 628 nm (corresponding to the LP mode). These spectral responses are attributed to cavity-induced field modulation, which enhances exciton generation beyond the primary absorption band of MDMO-PPV. Overall, this work demonstrates that combining photomultiplication mechanisms with cavity-field engineering provides an effective strategy for realizing narrowband, high-gain polaritonic photodetectors that surpass the spectral response limitations of conventional organic semiconductors.