Tailoring hole-selective contacts via self-assembled monolayers for advancing indoor organic photovoltaic and capacitor devices

Amidst the growing demand for transparent devices, the current research is centered on the advancement of technologies involving self-assembled monolayer (SAM)-treated transparent conductive electrodes. However, the detailed mechanisms governing surface energy reactions in these devices at the molecular scale remain unclear, underscoring the need for additional investigations. This study explored the effect of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) derivatives (MeO-2PACz, 2PACz, Br-2PACz) with a carbazole core on the properties of indium tin oxide (ITO) electrodes. On adsorbing 2PACz molecules onto the ITO surfaces, interfacial dipoles formed through chemisorption between the phosphonic acid oxygen and indium atoms, elevating the work function (WF). 2PACz treatment enhanced the electronic properties of the electrodes for indoor organic photovoltaics (OPV) and metal–insulator-metal (MIM)-capacitors. The optimized Br-2PACz-based indoor OPVs achieved a remarkable 31.0 % power conversion efficiency and an excellent fill factor of 78.0 % under LED 1000 lx conditions. Furthermore, Br-2PACz-based MIM-capacitors exhibited a reduction in leakage current greater than 19,000 times compared to that of the TiN-electrode-based MIM-capacitors. These outstanding electronic device achievements were attributed to the elevated WFs of the electrodes achieved through the 2PACz treatment. This research underscores the manifold enhancements in device performance achieved through refined energy-level alignment stemming from the increased WFs facilitated by SAM integration.