Premium
Organic Photovoltaic Cells Based On Solvent‐Annealed, Textured Titanyl Phthalocyanine/C 60 Heterojunctions
Author(s) -
Placencia Diogenes,
Wang Weining,
Shallcross R. Clayton,
Nebesny Kenneth W.,
Brumbach Michael,
Armstrong Neal R.
Publication year - 2009
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200801723
Subject(s) - materials science , homo/lumo , phthalocyanine , photocurrent , heterojunction , energy conversion efficiency , thin film , x ray photoelectron spectroscopy , open circuit voltage , organic solar cell , phase (matter) , optoelectronics , analytical chemistry (journal) , photochemistry , nanotechnology , chemistry , chemical engineering , polymer , organic chemistry , molecule , voltage , physics , quantum mechanics , engineering , composite material
Organic photovoltaic cells (OPV) with good near‐IR photoactivity are created from highly textured titanyl phthalocyanine (TiOPc)/C 60 heterojunctions. Vacuum deposited TiOPc thin films are converted to the near‐IR absorbing “Phase II” polymorph using post‐deposition solvent annealing. The Phase I → Phase II transition broadens the absorbance spectrum of the Pc film producing absorptivities ( α ≈ 10 5 cm −1 ) from 600–900 nm, along with substantial texturing of the Pc layer. Atomic force microscopy and field‐emission scanning electron microscopy of the solvent annealed films show that the surface roughness of the Pc layers is increased by a factor of greater than 2× as a result of the phase transformation. Current–voltage ( J – V ) responses for white light illumination of ITO (100 nm)/TiOPc (20 nm)/C 60 (40 nm)/BCP (10 nm)/Al (100 nm) OPVs show a near doubling of the short‐circuit photocurrent ( J SC ), with only a small decrease in open‐circuit photopotential ( V OC ), and a concomitant increase in power conversion efficiency. Incident photon current efficiency (IPCE) plots confirmed the enhanced near‐IR OPV activity, with maximum IPCE values of ca. 30% for devices using Phase II‐only TiOPc films. UV‐photoelectron spectroscopy (UPS) of TiOPc/C 60 heterojunctions, for both Phase I and Phase II TiOPc films, suggest that the Phase II polymorph has nearly the same HOMO energy as seen in the Phase I polymorph, and similar frontier orbital energy offsets, E HOMO Pc – E LUMO C60 , leading to comparable open‐circuit photovoltages. These studies suggest new strategies for the formation of higher efficiency OPVs using processing conditions which lead to enhance near‐IR absorptivities, and extensive texturing of crystalline donor or acceptor films.