High detectivity, efficient, ambient-stable inverted organic photodetectors incorporating a conjugated polymer as an electron transport layer

Abstract

We demonstrate highly sensitive, efficient, ambient-stable organic photodetectors (OPDs) in an inverted platform. The bilayer structure of poly{[N,N′′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′bithiophene)}/poly[9,9-bis(6′-(N,N-diethylamino)propyl)-fluorene-alt-9,9-bis-(3-ethyl(oxetane-3-ethyloxy)-hexyl)-fluorene] (N2200/PFN-OX) with hydrophobic surface characteristics is implemented as an electron-transport layer (ETL) for the fabrication of ITO/N2200/PFN-OX/P3HT:PCBM/MoO₃/Ag bulk heterojunction type OPDs. Devices with a 15-nm-thick N2200/PFN-OX layer are able to produce an ultra-low dark current density of 1.58 × 10⁻¹¹ A cm⁻² at 0 V, a faster response time of 4.9 μs, a wide linear dynamic range (LDR) value of >138 dB, and an impressive detectivity of 1.20 × 10¹⁴ cm Hz^1/2 W⁻¹. Additionally, after 63 days, the OPDs retain 85% and 70% of their initial responsivity and detectivity, respectively, in contrast to those with hydrophilic ZnO as the ETL having 70% and 30% residuals, respectively. The superior performance of the proposed OPDs can be attributed to the hydrophobic surface characteristics of the polymer bilayer, which enables the formation of an excellent interface with the photoactive layer to facilitate charge transport and minimize the influence of water molecules. Our approach is very useful and can be generalized to other highly efficient photoactive blends and even other organic optoelectronic devices for developing high-performance, ambient-stable devices.