All‐Inkjet‐Printed, All‐Air‐Processed Solar Cells

Abstract

deposition processes. Despite impressive progress over the last decade, OPVs are still some way behind other thin-fi lm technologies harvesting solar energy because of low effi ciencies and short lifetimes. [ 5 ] Materials for OPVs such as the semiconducting polymers, transparent electrodes, substrates, and encapsulant materials are not cheap enough to be competitive for large-area power generation. Nevertheless, there are small-scale, energy harvesting applications where OPVs are required to be locally printed to provide electric power to the system. For example, system-in-foil devices could include sensor components, OPVs for energy harvesting, a thin fi lm battery for energy storage, and an organic light-emitting diode (OLED) array as a display and electronic circuitry on a single substrate. [ 6 ] To date, no route is available for monolithically integrating solar cells into a system in which other components such as transistors, sensors, or displays are already fabricated.Here, we report for the fi rst time the fabrication and measurement of all-inkjet-printed, all-air-processed organic solar cells with the structure poly(3,4-ethylenedioxythi ophene):polystyrene sulfonate (PEDOT:PSS)/poly[N-9′heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole)]:[6,6]-phenyl-C71-butyric acid methyl ester (PCDTBT:PC 70 BM)/ZnO/Ag. A schematic diagram of the printed solar cell structure and the energy level diagram of its components is presented in Figure 1 . Among the various printing methods, inkjet-printing technology has been selected here for the fabrication of all-printed bulk-heterojunction solar cells because of its capability to locally deposit small volumes of functional inks without a mask and with high positional accuracy and low cost. Inkjet printing has proven effective in fabrication of OLEDs, [ 7 ] thin-fi lm transistors, [ 8 ] and photodetectors, [ 9,10 ] and was recently applied to fabricate either an active layer or an anode of OPVs. [11][12][13][14] We demonstrate a high-effi ciency solar cell with a homogeneous inkjet-printed donor-acceptor thin fi lm which was achieved by engineering the semiconducting blend ink with a tailored ternary solvent. Atomic force microscopy (AFM), grazing incidence wide-angle X-ray scattering (GIWAXS), and transient absorption spectroscopy are used to explore surface morphology, fi lm microstructure, and polaron dynamics in both inkjet-printed and spin-coated PCDTBT:PCBM fi lms. The results have shown that our inkjet-printed blend layer exhibits similar nanoscale structure and excited state dynamics to its spin-coated counterparts.The prospective of using direct-write printing techniques for the manufacture of organic photovoltaics (OPVs) has made these techniques highly attractive. OPVs have the potential to revolutionize small-scale portable electronic applications by directly providing electric power to the systems. However, no route is available for monolithically integrating the energy-harvesting units into a system in which other components, suc...

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