Effects of Ionic Liquid Molecules in Hybrid PbS Quantum Dot–Organic Solar Cells

We investigated the effect of ionic liquid molecules (ILMs) in hybrid quantum dot-organic solar cells (HyQD-OSCs). The insertion of an ILM layer between PbS and phenyl-C61-butyric acid methyl ester (PCBM) can shift the band edge of PCBM closer to the vacuum level of PbS due to spontaneous dipole polarization. Because of this new architecture, improvements in device performance were achieved, including increases in open-circuit voltage (VOC, from 0.41 V to 0.49 V), fill factor (FF, from 0.48 to 0.59), and power conversion efficiency (PCE, from 1.62% to 2.21%), compared to reference devices under AM 1.5G illumination at 100 mW cm(-2). We observed that treatment of the PbS layer with ILMs causes a significant increase in work function from 3.58 eV to 3.93 eV. Furthermore, the ILMs layer minimizes the contact resistance between PbS and PCBM due to the improved compatibility between the two layers, confirmed as a decrease in charge transfer resistance, as measured by electrical impedance spectroscopy.