Photomultiplication type organic photodetectors with different response characteristics under forward or reverse bias

Photomultiplication type organic photodetectors (PM-OPDs) with a sandwich structure of ITO/PNDIT-F3N/P3HT:[71]PCBM(100:1, wt/wt)/Al were successfully developed, exhibiting different response characteristics under forward or reverse bias. The rather less [71]PCBM can act as isolated electron traps to capture photogenerated electrons. The trapped electrons near ITO (Al) electrode can make interfacial band bending for hole tunneling injection from external circuit under forward (reverse) bias. The injected holes can be efficiently transported along the channel provided by P3HT and then collected by the corresponding electrode under bias. The external quantum efficiency (EQE) spectral shape of PM-OPDs is primarily determined by the trapped electron distributions near ITO or Al electrode under forward or reverse bias. The PM-OPDs exhibit flat EQE spectra under forward bias and 'M-shaped' EQE spectra under reverse bias, which is consistent with the curves of trapped electron distribution near ITO or Al electrode. The champion EQE values of PM-OPDs arrive to 2550% at 425 nm under 10 V bias and 2360% at 365 nm under −10 V bias. The PM-OPDs exhibit distinct response speed under forward or reverse bias, which is primarily attributed to the different trapped electron density near ITO or Al electrode under incident light from ITO side.