Solvents effects on the hole transport layer in organic solar cells performance

Abstract

Improving the morphology of the poly (3,4-ethylenedioxy-thiophene) and polystyrene sulfonate acid (PEDOT:PSS) that is used as a hole transport layer (HTL) in organic solar cells (OSCs) can enhance OSC parameters. Solvents are the most successful method to improve the properties of PEDOT:PSS as HTL for OSCs. It is found that fresh PEDOT:PSS contains a number of PEDOT-rich agglomerates that reduce light absorption and charge extractions of photo-generated charge carriers. As a result, these agglomerates block the hole extraction to the electrode, decreasing the power conversion efficiency (PCE). We investigated a method to control PEDOT-rich agglomerates in PEDOT:PSS thin films. For this purpose, solvents such as isopropyl alcohol (IPA), ethanol, and methanol were investigated. We found the treatment of PEDOT:PSS with IPA solvents substantially reduced a number of PEDOT-rich agglomerates while ethanol and methanol solvents slightly reduced PEDOT-rich agglomerates. The consequence of controlled PEDOT-rich agglomerates was improved light absorption as well as improved photovoltaic parameters such as current density, fill factor, and open circuit voltage of organic solar cells. The improved performance of organic solar cells can be interpreted as the enhanced charge carrier extraction efficiencies between PEDOT:PSS and the photoactive layer of organic solar cells.