Highly transparent and conductive MoO3/Ag/MoO3 multilayer films via air annealing of the MoO3 layer for ITO-free organic solar cells

Abstract

Air annealing of MoO 3 bottom layer is a simple and highly efficient surface treatment method to prepare ultrathin, continuous, and smooth Ag layers in MoO 3 /Ag/MoO 3 (MAM) transparent conductive films (TCFs) for indium tin oxide (ITO)-free organic solar cells (OSCs). Air annealing can readily oxidize MoO 3 surface and increase surface energy of the MoO 3 layer, which significantly enhances the adhesion between Ag and MoO 3 . When the MoO 3 bottom layer is annealed at 200 °C, moreover, the treatment yields a flatter MoO 3 surface, which positively influences the growth of Ag nanostructures . Eventually, an almost homogeneous, smooth, and continuous surface morphology of the ultrathin Ag films with a thickness of 6.5 nm was obtained. By employing air-annealed MoO 3 bottom layer, the MoO 3 (200 °C, 10 min)/Ag (6.5 nm)/MoO 3 TCF had higher optical transmittance (T av = 83.6%) and lower sheet resistance (R s = 6.5 Ω/sq) than unannealed MAM or commercial ITO TCFs, thereby obtaining the higher value of figure of merit (F TC = 2.6 ×10 −2 Ω −1 ). When used as the transparent electrode in organic solar cells (OSCs), the improved optoelectrical properties of the MoO 3 (200 °C, 10 min)/Ag (6.5 nm)/MoO 3 electrode result in increased short-circuit current density (J sc = 2.27 mA cm −2 ) and fill factor (FF = 54.8%) of OSCs in comparison to devices based on unannealed MAM and ITO electrodes, leading to an improvement in power conversion efficiency (PCE = 0.62%). From the results of photocurrent measurements, air annealing MoO 3 increases exciton generation in active layers and reduces the carrier back-transfer induced recombination at the anode contact, yielding the enhanced photovoltaic performance .

Topics & Concepts