| At Present, the major bottleneck of the development of OPV is the lowphotoelectric conversion efficiency (PCE), which couldn’t reach therequirements of industrialization application. So, how to improve its PCE hasbecome a hot research in academia and industry all over the world. In this work,we proposed a very simple, convenient and low cost technique to prepare arandomly and irregularly structured PEDOT:PSS buffer layer, and incorrporatesuch buffer layer into small molecule solar cell based on CuPc/C60system. Theresearch contents and results are shown as follows:1. The nanostructured PEDOT:PSS films are fabricated on ITO/glasssubstrates by blending-spin coating method. The surface topography of thenanostructured PEDOT:PSS layer on ITO/glass substrate before and afterdepositing photoactive layers have been studied by Dektak XT probeprofilometer and atom force microscope (AFM), The results clearly indicate thatsome irregular nano-holes are randomly distributed within PEDOT:PSS layer,and the embossed feature can be extended to C60layer to form some bowl-shaped morphology in C60surface. The maximum concave-convex heightis reduced from about40nm in PEDOT:PSS layer to about8nm in C60layer.2. We investigated the total reflectance and transmission spectra ofnanostructured PEDOT:PSS on ITO/glass substrate, and the light trappingability of the nanostructured photoactive layers have been studied. The totalreflectance intensity of the structured PEDOT:PSS layer is obviously lower thanthat of the planar PEDOT:PSS in the wavelength range of370-850nm. Thisindicates that the randomly and irregularly embossed PEDOT:PSS has excellentanti-refection ability across a broad wavelength regime. In the wavelengthregion of more than500nm, the structured PEDOT:PSS film fabricated by200nm PS ball has better anti-refection effect than that by500nm PS ball, while inthe wavelength region of350-500nm the reverse results are observed. The totaltransmission intensity of the structured PEDOT:PSS layer is also slightly lowerthan that of the planar PEDOT:PSS. The reduced reflection and transmission ofthe structured PEDOT:PSS mean that much more light is trapped within thenon-periodic structured PEDOT:PSS layer. The total absorption of the activelayer deposited on the structured PEDOT is higher than that on the planarPEDOT across the entire wavelength range of400-850nm, indicating thehigher light trapping capability of the structured photoactive layer, which is inaccordance with the optical property of the structured PEDOT:PSS layer.3. We investigate the effects of the structured PEDOT:PSS layer on theperformances of small molecule organic solar cell. The experiments confirm the application of structured PEDOT:PSS in small molecule solar cell can improvephotoelectric properties of OPV device. For the structured device fabricated byPS ball of200nm diameter, the maximal value of PCE is enhanced to0.767%with the enhancement factor of25.5%relative to the planar cell and with theenhancement factor of8.86%relative to the structured device fabricated by PSball of500nm diameter (PCE=0.733%). The improvement of photoelectricproperties of the nanostructured devices is primarily governed by two majorfactors, first, the nanostructured device increases the amount of photons trappedin active layer owing to the increased optical path of incoming light and thusresults in the higher electron-hole pair generation. In addition, thenanostructured PEDOT:PSS layer also enlarge junction area at the interfaces ofCuPc/C60, CuPc/PEDOT:PSS and C60/cathode, which improve the efficienciesof charge separation and carrier collection/transport.4. The effects of the structured PEDOT:PSS layer on the performances ofhole-only devices have been studied. Results suggest that the holes mobility ishigher in the structured device than in the planar device. |
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