Enhancing the performance of photomultiplication-type organic photodetectors using solution-processed ZnO as an interfacial layer†
As a promising alternative to conventional photodiode-type organic photodetectors (OPDs), photomultiplication (PM)-type OPDs can achieve much higher external quantum efficiencies (EQEs) over 100% and work as optical amplifiers for real applications. Here, high-performance PM-type OPDs with a structure of ITO/ZnO/P3HT : O-IDTBR (100 : 1, w/w)/Al are fabricated by using solution-processed zinc oxide (ZnO) as an interfacial layer. The resulting OPDs exhibit a broad spectral-response range (EQE > 100%) from 300 to 780 nm under −15 V bias, while the range is only from 320 to 720 nm for the OPDs with a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) interfacial layer. The extended spectral-response in the ultraviolet (UV) region for the OPDs based on ZnO is attributed to the fact that UV light can be absorbed by the ZnO interfacial layer. Under −15 V bias, the optimized ZnO-based OPDs exhibit the highest EQE of 3660%, with a responsivity of 12.10 A W−1 and a detectivity of 1.02 × 1013 Jones at 410 nm. By contrast, optimized PEDOT:PSS-based OPDs show an EQE of 1010%, with a responsivity of 3.34 A W−1 and a detectivity of 1.47 × 1012 Jones under the same conditions. Compared with the PEDOT:PSS-based OPDs, the ZnO-based OPDs show a broader spectral-response range with more than 2.6 times larger EQE and responsivity, as well as more than 5.9 times larger detectivity in a short wavelength range under −15 V bias.