Abstract
In this thesis, I focus on the optical properties and device engineering of vacuum-deposited organic optoelectronics. In the first part, I briefly review the development of organic solar cells (OSCs), followed by working mechanisms, device structures of OSCs, material analyses, device deposition methods and measurements of OSCs. In the second part of thesis, 1,4,5,8-napthalene-tetracarboxylic-dianhydride (NTCDA) and 3,4,9,10-perylenetetracarboxylic-bisbenzimidazole (PTCBI) were used to replace 2,9-dimethyl-4,7-di(phenyl)-1,10-phenanthroline (BCP) as optical spacing layer in OSCs. Furthermore, a Ca buffer layer is capped on PTCBI to modify morphological roughness. In addition, an effective bilayer cathode buffer layer for highly efficient small molecule organic solar cells (SMOSCs) is demonstrated. By integrating 4,7-di(phenyl)-1,10-phenanthroline (Bphen)/1 nm Ca bilayer buffer layer, the power conversion efficiency (PCE) enhances over 20 % compared to a device with a traditional Bphen buffer layer. In the third part, before evaluating new donor compounds for SMOSCs, I review some previous studies of small molecular donors employed in SMOSCs . Among all donor-acceptor (D-A) structured donor compounds in this study, DT4MIDTP, a donor with the donor-π bridge-acceptor-acceptor (D-π-A-A) molecular structure, shows the best performance by utilizing the planar mixed heterojunction (PMHJ) structure. The optimized blend ratio is DT4MIDTP:C70 = 1:1 (by volume), giving a PCE of up to 4.22 %. The PCE further improves to 4.6 % by utilizing the tandem PMHJ structure. The electrical and optical properties of DT4TIDTP and DT4MIDTP films after thermal annealing are also investigated. With appropriate pre-annealing treatment, the performance of DT4MIDTP device with planar heterojunction structure improves from 1.3 % to 2.5 %. DTPTtDCV, a donor with oligothiophene core, shows the most promising characteristics among all oligothiophene core donor systems in this study with best PCE up to 3.02 %. In the last part of this thesis, by the aid of our home-made optical simulation program, micro-cavity organic photodetectors (OPDs) with high photoresponsitivity across the entire visible region are demonstrated. In order to enhance the photoresponse of a particular wavelength region, the thicknesses of transparent anti-reflection layers and hole transporting layers are modeled and designed. The OPDs with enhanced photoresponse at target wavelengths are realized. Finally, an in-situ all-vacuum-deposition method to fabricate controllable periodic wrinkling surfaces is demonstrated. By utilizing these wrinkling surfaces as light trapping and light scattering layer in organic optoelectronics, efficient devices with enhanced light in-coupling/out-coupling efficiency are demonstrated.