Highly efficient polymer solar cells based on a universal cathode interlayer composed of metallophthalocyanine derivative with good film-forming property

Abstract

A new cathode interlayer (CIL) material metallophthalocyanine (MPc) derivative 1,4,8,11,15,18,22,25-octaoctyloxy-2,3,9,10,16,17,23,24-octa-[N-methyl-(3-pyridyloxy)] zinc-ylphthalocyanine iodide (1 : 8) (ZnPc(OC₈H₁₇OPyCH₃I)₈) was 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), P3HT:PC₆₁BM (P3HT = poly(3-hexylthiophene), PC₆₁BM = [6,6]-phenyl C61-butyric acidmethyl ester) or PCDTBT:PC₇₁BM (PCDTBT = poly[N-9′′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]) as an active layer. As a result, power conversion efficiency (PCE) values of the PSCs were 8.52%, 4.02% and 6.88%, respectively, which are much higher than those of corresponding PSCs with the Al-only cathode. It indicates that ZnPc(OC₈H₁₇OPyCH₃I)₈ is a new promising candidate as a universal CIL for highly efficient PSCs. Compared to VOPc(OPyCH₃I)₈ (2,3,9,10,16,17,23,24-octakis-[N-methyl-(3-pyridyloxy)] vanadylphthalocyanine iodide (1 : 8)), the PSC with ZnPc(OC₈H₁₇OPyCH₃I)₈ as a CIL has higher short-circuit current and fill factor because ZnPc(OC₈H₁₇OPyCH₃I)₈ can form a better, denser, and more uniform film on the active layer than VOPc(OPyCH₃I)₈ as demonstrated by atomic force microscopy (AFM), energy-dispersive spectrum mapping on scan electron microscopy (SEM-EDS mapping) and contact angle measurements.