Comparison of self-assembled monolayers with long alkyl chains on ITO for enhanced surface properties and photovoltaic performance

Abstract

Self-assembled monolayers (SAMs) are used as interfacial layer up to a few nanometer thick in electronic devices to tune the morphological and charge transport properties. Herein, we studied indium titanium oxide (ITO) treatment by two different SAMs molecules involving long alkyl chains with boronic acid (BA) and phosphonic acid anchoring groups to improve the performance of organic solar cells (OSCS). It was determined that the wettability of ITO increased due to the improved surface energy after SAM treatment, which led to enhanced morphology of upper layer. The champion device treated with C-14-BA SAM showed a power conversion efficiency (PCE) of 3.3%, which is higher than that of non-treated device (2.9%). The C-14-BA SAM treated ITO showed a better morphology and its device shows the highest performance, thanks to improved short circuit current (J(sc)) from 7.8 mA cm(-2) (for non-treated device) to 8.8 mA cm(-2). It was concluded that the work function change and upper layer morphology can be easily controlled by treatment of the ITO surface by SAMs with different anchoring groups. This study provides an easy and alternative approach to enhance the surface properties of metal oxides for improving the performances of OSCs.