Inverted Organic Solar Cells with Oxidized Carbon Materials as Effective Hole Transport Layer

In recent, organic solar cells (OSCs) have been advanced dramatically and had big attention as one of the most promising solar cells. However, it is still a challenge to manufacture OSCs with high efficiency and long-term stability in all layers. For solving these problems gradually, many researchers have studied insightfully about each layer including active layers and charge transporting layers in the device structure of OSCs. In particular, the introduction of the charge transporting layers can minimize charge recombination at the interface between the active layer and metal electrode. As the most commonly used hole transporting layer (HTL), PEDOT:PSS has been utilized as an anode interfacial layer to improve the contact between HTL and electrode and to increase hole collection in OSCs. Nevertheless, PEDOT:PSS layer has several drawbacks including moisture absorbing property, high acidity, and some electrical interruption properties, leading to direct damages in device performance. Therefore, it is required to develop new HTLs for improving the device performance and stability. In this study, we demonstrate oxidized recycling carbon nanoparticles (NPs) as an efficient HTL for OSCs for the first time. For carbon neutrality, the development of the recycling oxidized carbon NPs can suggest new applications and technologies. We prepared inverted OSCs including the interlayers with oxidized carbon soot (OCS) and functionalized OCS (F-OCS) NPs, enhancing the hole transporting properties and minimizing the contact resistance. As a result, the high device performance of 14.22% (PM6:Y6/OCS) and 14.17% (PM6:Y6/F-OCS) compared with PM6:Y6-based devices (13.52%) were achieved. The effects of OCS-based HTLs were thoroughly analyzed by using UV-Vis absorption, AFM, TEM, and conductivity measurements.