Organic Photovoltaic Cells Based On Solvent‐Annealed, Textured Titanyl Phthalocyanine/C₆₀ Heterojunctions

Abstract

Organic photovoltaic cells (OPV) with good near‐IR photoactivity are created from highly textured titanyl phthalocyanine (TiOPc)/C60 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 ≈ 105 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)/C60 (40 nm)/BCP (10 nm)/Al (100 nm) OPVs show a near doubling of the short‐circuit photocurrent (JSC), with only a small decrease in open‐circuit photopotential (VOC), 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/C60 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, EHOMOPc–ELUMOC60, 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.

New Electron Transport Materials for High Performance Organic Solar Cells: Synthesis and Properties of Symmetrical and Asymmetrical 1,4,5,8‐Naphthalenetetracarboxylic Dianhydride Derivatives

“…Various ETMs, such as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), [ 10 ] 1,3,5-tris(phenyl-2-benzimidazolyl)-benzene (TPBi), [ 11 ] and 4,7-diphenyl-1,10-phenanthroline (Bphen), [ 12 ] have been integrated into small molecule OSCs. [ 13 ] However, BCP, which found wide usage as an electron transport layer (ETL) in OLEDs [ 14 ] and OSCs [ 15 ] possesses such disadvantages, as thermal instability, and easy crystallization in the presence of moisture and at high temperature. [ 16 ] The derivatives of naphthalenetetracarboxilic dianhydride are good candidates for electron transporting layer in OPVs due to their high electron affi nity (EA), planar confi guration, excellent electron transport, and tunable optical and electrochemical properties.…”

On the Novel Biaxial Strain Relaxation Mechanism in Epitaxial Composition Graded La1−xSrxMnO3 Thin Film Synthesized by RF Magnetron Sputtering

“…These materials can present unique properties such as insulators in thin film transistors [3], thermoelectric conversion [4], optical spacers or electron/hole blocking/transporting layer in photovoltaic systems [5,6] biomaterial manufacturing [7], and aerospace technologies [8]. Out-of-plane composition gradient, as well as coherent epitaxy films, namely epitaxial composition graded (ECG) films as a category of FGMs, have been studied recently since their physical properties can be significantly modified by lattice strain [9].…”

Fabrication and characterization of organic solar cells using metal complex of phthalocyanines

“…Many studies on the modified phthalocyanine with various central metals and chemical substitutions have been reported to optimize open circuit voltage and conversion efficiency [7,8]. A lead phthalocyanine (PbPc) has several crystal structures with phase transition between H aggregate and J aggregate [9,10]. The H aggregate has high conductivity (10 2 S cm 1 ), and the J aggregate has low conductivity (10 10 S cm 1 ) [11].…”