Cationic Water-Soluble Conjugated Polyelectrolytes/Graphene Oxide Nanocomposites as Efficient Green Hole Injection Layers in Organic Light Emitting Diodes

The current research presents using a nanocomposite comprising of a cationic conjugated polyelectrolyte (CPE), poly­[(2,5-bis­(2-(<i>N</i>,<i>N</i>-diethylammonium bromide)­ethoxy)-1,4-phenylene)-<i>alt</i>-1,4-phenylene] or (PPPNEt₂·HBr), with graphene oxide (GO) as a new hole injection layer (HIL) for organic light emitting diodes. It is demonstrated that using the designed ionically functionalized water-soluble conjugated polymers instead of polyethylene dioxythiophene:polystyrenesulfonate (PEDOT:PSS) is a promising approach to overcome the strong acidic nature of PEDOT:PSS besides excluding its nonconductive PSS part. As the other aspiration of this work, we introduce a good partner for dissolving and spin-casting of GO as a simple and economic technique to use the hole conductive and electron blocking nature of GO in the hole injection portion of assembled devices. Using this new binary blend showed enhanced charge carrier mobility, good electroluminescence, and <i>J</i>–<i>V</i> characteristics in comparison with conventional devices. Such improvement is interpreted with induced ion space charge of HIL at the interface and resulting electric field screening effect due to ion migration

Photoinduced Self-Gating of Perovskite Photovoltaic Cells in Ionic Liquid

We demonstrate that the power conversion efficiency (PCE), photocurrent, and fill factor (FF) of perovskite solar cells (PSC) can be significantly improved by the photoinduced self-gating in ionic liquids (ILs) via n-doping of the carbon nanotube (CNT) top electrode on the fullerene electron transport layer (ETL). CNTs, graphene, and other carbon electrodes have been proven to be stable electrodes for PSC, but efficiency was not high. We have previously shown that the performance of PSCs with CNT electrodes can be improved by IL gating with gate voltage (Vg) applied from an external power source. Here we demonstrate that effective self-gating in ILs is possible by a photoinduced process, without an external source. The open circuit voltage (Voc) generated by the PSC itself can be applied to the CNT/C60 electrode as Vg leading to photogating. This self-gating with Voc is compared to photocharging of CNTs in ILs without any gating for two types of fullerene ETLs: C60 and C70, Two types of ILs, DEME-TFSI and BMIM-BF4, are tested for two types of nanotubes electrodes: single wall (SWCNT), and multiwall (MWCNT). The resulting improvements are analyzed using the effective diode-circuit (DC) and the drift-diffusion (DD) models. Self-gating allows the PCE improvement from 3–5% to 10–11% for PSCs with a thick ETL, while for optimal combination of a thin SWCNT/ETL with added layers for improved stability, the PCE reached 13.2% in DEME-TFSI IL