Alcohol/water-soluble porphyrins as cathode interlayers in high-performance polymer solar cells

Three alcohol/water-soluble porphyrins (Zn-TPyPMeI:zinc(II) meso-tetra(N-methyl-4-pyridyl) porphyrin tetra-iodide, Zn-TPyPAdBr:zinc(II) meso-tetra[1-(1-adamantylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide and MnCl-TPyPAdBr:man-ganese(III) meso-tetra[1-(1-adamantylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide were employed as cathode interlayers to fabricate polymer solar cells (PSCs). The PC71BM ([6,6]-phenyl C-71 butyric acid methyl ester) and PCDTBT (poly[N-9aEuro(3)-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)])-blend films were used as active layers in polymer solar cells (PSCs). The PSCs with alcohol/water-soluble porphyrins interlayer showed obviously higher power conversion efficiency (PCE) than those without interlayers. The highest PCE, 6.86%, was achieved for the device with MnCl-TPyPAdBr as an interlayer. Ultraviolet photoemission spectroscopic (UPS), carrier mobility, atomic force microscopy (AFM) and contact angle (theta) characterizations demonstrated that the porphyrin molecules can result in the formation of interfacial dipole layer between active layer and cathode. The interfacial dipole layer can obviously improve the open-circuit voltage (V (oc)) and charge extraction, and sequentially lead to the increase of PCE.