New small molecule electrolytes based on tosylate anion for organic solar cells

Abstract

Reduction of a Schottky barrier between the active layer and electrodes can play an important role enhancing the power conversion efficiency (PCE) of organic solar cells (OSCs), which originated from a favorable interface dipole at the cathode interface. Herein, two new small molecules (SM) electrolytes based on tosylate anions, named 2,2’-(ethane-1,2-diylbis(oxy))bis(N,N,N-trimethylethananminium) benzenesulfonate (TEG-M-OTs) and 1,1'-bis(1-dodecyl)-4,4′-bipyridine-1,1′-diium benzenesulfonate (V-C12-OTs), were synthesized to induce the reduction of a Schottky barrier in OSCs. The PCE of devices based on ZnO with TEG-M-OTs or V-C12-OTs as the cathode buffer layer (CBL) was enhanced from 7.48% to 7.74% and 7.88%. In case of ZnO-free devices, the PCE of TEG-M-OTs or V-C12-OTs was achieved up to 4.22% and 6.95%, respectively. The Kelvin probe microscopy was performed by measuring the work function (WF) of SM electrolytes with or without ZnO on the ITO surface. It showed that the WFs of SM electrolytes coated ITO are closer to - 4.02 eV, the lowest unoccupied molecular orbitals (LUMO) of the acceptor, than the WF of MeOH treated ITO with ZnO (- 4.37 eV).

Acknowledgment

This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20194010201840) and was supported by the BB21+ Project in 2018.