UV–Ozone Modified Sol–Gel Processed ZnO for Improved Diketopyrrolopyrrole-Based Hybrid Photodetectors

• Published in: ACS applied electronic materials 2019-11, Vol.1 (11), p.2455-2462
• Main Authors: Pickett, Alec, Mohapatra, Aiswarya A, Ray, Suman, Lu, Qiangsheng, Bian, Guang, Ghosh, Kartik, Patil, Satish, Guha, Suchismita
• Format: Article
• Language: English
• ISSN: 2637-6113; 2637-6113
• DOI: 10.1021/acsaelm.9b00597

Organic–inorganic interfaces in photodiodes have recently gathered significant interest due to the realization of intrinsic p–n junctions and unique physical properties. Nanopatterned sol–gel ZnO films provide an alternate path for fullerene-free organic photodetectors. However, naturally occurring oxygen vacancies in ZnO often act as trap sites and can degrade device performance if left unchecked. Here, we focus on the role of UV–ozone treatment for filling oxygen vacancies in sol–gel processed ZnO for improving the hybrid interface with thienothiophene linked diketopyrrolopyrrole (DPP) films. The ZnO films are characterized by X-ray diffraction, ultraviolet photoelectron spectroscopy (UPS), cross-sectional electron microscope images, and electron energy loss spectroscopy (EELS). UV–ozone treatment shows no change in the crystal structure, but UPS indicates that the treated films are more resistive and have a higher oxygen concentration at the surface. The EELS spectra show gradual passivation of oxygen vacancies within the bulk of the ZnO films. Fullerene-free photodetectors fabricated from ZnO:DPP interfaces show dark currents reduced by half and photoresponsivities nearly doubled, on average, when the ZnO surface is UV–ozone treated compared to nontreated ZnO films, indicating this simple technique to be excellent for improving photodiode performance when ZnO is used as an electron transport layer.