Metallophthalocyanine derivatives utilized as cathode interlayers for polymer solar cells: a practical approach to prepare a uniform film

Abstract

Three metallophthalocyanine derivatives: 2,3,9,10,16,17,23,24-octakis-[N-ethyl-(3-pyridyloxy)]vanadylphthalocyanine bromine (1 : 8) (VOPc(OPyC₂H₅Br)₈), 2,3,9,10,16,17,23,24-octakis-[N-butyl-(3-pyridyloxy)]vanadylphthalocyanine bromine (1 : 8) (VOPc(OPyC₄H₉Br)₈) and 2,3,9,10,16,17,23,24-octakis-[N-hexyl-(3-pyridyloxy)]vanadylphthalocyanine bromine (1 : 8) (VOPc(OPyC₆H₁₃Br)₈) were synthesized and applied in polymer solar cells (PSCs) based on PTB7:PC₇₁BM (PTB7 = thieno[3,4-b]thiophene/benzodithiophene, PC₇₁BM = [6,6]-phenyl C₇₁-butyric acidmethyl ester) as an active layer. As a result, the highest power conversion efficiency (PCE) value of the PSCs is 7.99% for the device with VOPc(OPyC₂H₅Br)₈ as a cathode interlayer. Although increasing the alkyl side chains attached to the pyridine functional groups of phthalocyanine leads to a slight decrease of PCE, VOPc(OPyC₆H₁₃Br)₈ can form a better, denser and more uniform film on the active layer as demonstrated by atomic force microscopy, energy dispersive spectrum mapping and contact angle measurements.