Improvement of organic solar cells using aluminium microstructures prepared in PEDOT:PSS buffer layer by using ultrasonic ablation technique

Abstract

In the present work we introduce an improvement of organic solar cell efficiency by using aluminium microstructures (Al MSs) dispersed in poly(3,4-ethylene dioxythiophene)-blend-poly(styrene sulfonate) (PEDOT:PSS) buffer layer. Al microstars (in the range of 5–16μm) in addition to Al nanoparticles (Al NPs) have been prepared by new ultrasonic ablation technique through the application of ultrasonic irradiation upon Al thin film immersed in PEDOT:PSS solution. In the beginning, we found that the PEDOT:PSS solution completely dissolves Al thin film before the applying of ultrasonic irradiation as a result of acidic nature of the PEDOT:PSS solution. The action of PEDOT:PSS on the Al film tends to produce Al microcircles, which are dissociated into Al microstars after the applying of ultrasonic irradiation. The short circuit current density, fill factor, and, consequently, power conversion efficiency of the investigated solar cells have been improved by the incorporation of Al microstars, which can facilitate the transport of charge carriers, specifically holes, to be transferred along the axis of the Al microstars in the buffer layer of the solar cell. We found that the increase in ultrasonication time applied upon the solution of PEDOT:PSS-Al microstars diminishes the length of Al microstars and reduces the number of Al microstars' arms. Therefore, further increase in the ultrasonication time tends to decrease the device performance parameters due to the deficit of charge carriers to be transferred in the buffer layer matrix. The Al microstars prepared by ultrasonic ablation technique are pure and free of surfactants and passivation layers that are inevitably present on the surface of the chemically synthesized metal MSs and NPs. The new ultrasonic ablation method is safe (different than laser ablation technique) to prepare metal NPs and MSs in the sensitive organic solvents and solutions which are directly used to prepare organic solar cells. In addition, the new technique enables us to prepare desirable size of Al microstars, which can be suitable for improving organic solar cells and in other different applications.