Highly Conductive Transparent Organic Electrodes with Multilayer Structures for Rigid and Flexible Optoelectronics

Transparent electrodes are essential components for optoelectronic devices, such as touch panels, organic light-emitting diodes, and solar cells. Indium tin oxide (ITO) is widely used as transparent electrode in optoelectronic devices. ITO has high transparency and low resistance but contains expensive rare elements, and ITO-based devices have poor mechanical flexibility. Therefore, alternative transparent electrodes with excellent opto-electrical performance and mechanical flexibility will be greatly demanded. Here, organics are introduced into dielectric–metal–dielectric structures to construct the transparent electrodes on rigid and flexible substrates. We show that organic-metal-organic (OMO) electrodes have excellent opto-electrical properties (sheet resistance of below 10 Ω sq−1 at 85% transmission), mechanical flexibility, thermal and environmental stabilities. The OMO-based polymer photovoltaic cells show performance comparable to that of devices based on ITO electrodes. This OMO multilayer structure can therefore be used to produce transparent electrodes suitable for use in a wide range of optoelectronic devices.

. AFM images of PAPE with different Ag thickness.    Film samples (in the region around by the dash) with different structure have been deposited on the pattened ITO glass substrates, and resistance measurements have been carried out with a digital multimeter as shown in Fig. S7. In Figure S7(a), the resistances were measured through two ITO electrodes. For the PVK or PEDOT film, the resistance is over 2000 MΩ between the two bottom separated ITO electrodes, which is too large to be measured by our digital multimeter. But when a Ag layer was deposited on PVK film, or inserted between the PVK and PEDOT, resistance of 63 or 69 Ω was achieved which confirmed that the OMO electrode mainly conducted by the middle metal layer. In Figure S7(b), the resistances were measured through two top separated copper tape electrodes. Similar phenomenon was found as the aforementioned measurements in Fig. S7 Table S1. Sheet resistance of glass/PAPE and PET/PAPE film after repeated taping.
The AFM images of PVK and PVK/Ag films have been shown in Figure S9. The surface of the PVK film is smooth and the roughness is about 0.5 nm. When a 10 nm Ag was deposited on the PVK, a successive Ag layer can be seen in the AFM figure, and the roughness slightly increased to 1.9 nm. It illustrates that the smooth PVK film can provide a favorable environment for Ag growth.
The wettability between two films can be reflected through the mechanical adhesion. So the mechanical adhesion of the PAPE film on glass and PET were tested by taping with a tape, and the results have been shown in Table S1. The resistances of PAPE films on glass substrate and PET substrate were all unchanged after taping with a tape for three times. It illustrates that the adhesions between each layer of the PAPE film are large enough to against the tape.

Optical simulation
The characteristic matrix of PAP or PAPE on a glass substrate is S1 where j = 0 (for incidence medium); 1, 2, or 3 for OMO layers; or 4 for the substrate layer.
The angular phase thickness is . θ j is the angle of wave propagation in the layer as determined from Snell's law. N j denotes the refractive index of each layer, which is relevant to the incident wavelength λ. The physical thicknesses of the plate PVK (or PEDOT:PSS) exposed to air, the Ag plate, and the PVK plate on the glass substrate are represented by d 1 , d 2 , and d 3 , respectively. The transmittance can be given as Here, we only consider vertical incidence, thus, j j j d N λ π δ 2 = , and j j N = η . Using data of Ag, PVK and PEDOT:PSS from the literatures, S2-S4 we can simulate transmittance for PAP or PAPE with glass N 4 =1.52 or PI N4=1.75 as a substrate and under vertical incidence, by inputting j=1, 2, 3, N 1 = n 1 (λ)-ik 1 (λ), N 2 =n 2 (λ)-ik 2 (λ), N 3 = n 3 (λ)-ik 3 (λ), N 4 =1.52 (or N4=1.75) using a computer.