Rational design of a junction structure to realize an NIR-selective narrowband organic thin-film photodiode†
A color-filter-free near-infrared (NIR)-selective thin-film organic photodiode (OPD) is demonstrated by systematically controlling the correlation between the optical penetration region and the semiconductor junction depletion region. Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl] (PCE10):poly(3-hexylthiophene-2,5-diyl) (P3HT) or poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole)] (PPDT2FBT):poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) (p-complex) is used as a photoactive donor layer in conjunction with the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as a photoactive acceptor layer with well-defined abrupt PN junction characteristics. The device architecture is rationally designed such that the optical penetration regions of visible photons within the p-complex are isolated from the depletion region of a PN junction due to their high absorption coefficients, while those of NIR photons efficiently overlap with the depletion region due to their low absorption coefficients. This enables high performance NIR-selective OPDs with a peak detectivity over 1012 Jones centered at 705 nm or 780 nm depending on the chemical composition of the p-complex, while maintaining the thin film nature of the active layer, as well as efficient quenching of the photoelectric conversion of undesired visible photons. This is the first example showing that the narrowband NIR selectivity of a thin film OPD can be realized by controlling the relationship between the optical penetration region and depletion region rather than the thickness of the entire semiconductor.