Investigating Working Mechanism of Metallophthalocyanine Derivatives as a Cathode Interlayer in Polymer Solar Cells by Photoemission Spectroscopy

Abstract

Three metallophthalocyanine derivatives with different central metallocores (MPcXs, X = (OC8H17OPyCH3I)8), namely, ZnPcX, VOPcX, and TiOPcX, were synthesized and applied as a cathode interlayer (CIL) in the PTB7:PC71BM based polymer solar cells (PSCs). Power conversion efficiency (PCE) values reached 8.1% for the devices with Ag as the cathode, while the PCE values could reach 8.2% for the devices with Al as the cathode. Moreover the three MPcXs led to similar device performance in the PSCs with either Ag or Al as the cathode. It indicates that central metallocores in the MPcXs have a negligible effect on the device performance. Working mechanism of the MPcX as the CIL in the PSCs has been investigated by photoemission spectroscopy. Findings of ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS) demonstrated that the MPcX as the CIL not only decreased work function of the metal cathode and electron extraction barrier from PC71BM to cathode but also functioned as a buffe...