Effect of solvent vapor annealing on TiOPc thin films and the application on hybrid solar cells

This article reports on effect of solvent vapor annealing on TiOPc thin films and the application on hybrid solar cells based on ZnO/TiOPc with DH-alpha6T as an electron blocking layer. The band gap shows a change for the TiOPc thin film solvent vapor annealed with various solvents, which may be due to the phase transition from amorphous to alpha-phase, beta-form or alpha+beta-form. The phase separation could be responsible for the variations of the optical properties. No significant change is observed in the pi-pi* transition at various phase behaviors. Device performance of hybrid solar cells could be improved and open-circuit voltage (VOC), short-circuit current (ISC) and power conversion efficiency (eta) were enhanced by solvent vapor annealing, which originated from amorphous TiOPc films transformed into crystalline alpha-phase, beta-form or alpha+beta-form.nbsp At alpha-TiOPc, the device achieved the highest performance with VOC, ISC and eta of 0.57 V, 1.40 mA/cm2, and 0.22 %, respectively, which originated from alpha-TiOPc with the widest red and near-IR absorption band

Controlling the crystallinity and crystalline orientation of “shuttlecock” naphthalocyanine films for near-infrared optoelectronic applications

The thin film properties of tin(II) 2,3-naphthalocyanine (SnNPc) were interrogated and various strategies for controlling the crystallinity and crystalline orientation within the films were assessed. SnNPc is shown to crystallize in the space group P21/c (Z = 4), where the molecular arrangement consists of alternating layers of concave and convex overlap, induced by the out-of-plane Sn atoms, resulting in a 3D slipped-π-stack network structure analogous to that reported for Phase I of titanyl phthalocyanine. The thin films were studied by X-ray diffraction, atomic force microscopy and absorption spectroscopy and are highly sensitive not just to the conditions during growth, but also to substrate pre- and post-deposition treatment. While the films grown at room temperature were largely amorphous, the crystallinity was enhanced with substrate temperature, with the molecules orienting in a standing molecular geometry. A thin layer of 3,4:9,10-perlenetetracarboxylic dianhydride induces a lying molecular geometry of the same polymorph as that of the single crystal, while different polymorphs are accessible through solvent vapor annealing of amorphous films. Transient photocurrent measurements showed a dramatic improvement in photodetector device bandwidth for the lying molecular geometry, which was attributed to enhanced photoconductivity along the π-stacking axis, while solvent vapor annealing could be used to tune the photosensitivity across the near-infrared region

Experimental and Theoretical Investigations on the IR and Raman Spectra for CuPc and TiOPC

Vibrational IR and Raman powder spectra were recorded for copper phthalocyanine (CuPc) and titanyl (IV) phthalocyanine (TiOPc). Density functional theory (DFT) calculations have been used to predict the theoretical spectra and to assist reliable assignments of the experimental frequencies. There is, in general, a good agreement between experimental and theoretically predicted spectra. The best accordance between experiment and calculated wavenumbers was obtained in the case of the IR spectrum for CuPc (maximum deviations between experiment and theory (unscaled values) amount to less than 20 cm-1). New assignments for the IR and Raman spectra for both molecules were done in order to establish the basis for further work on thin films

Orientational Ordering of Nonplanar Phthalocyanines on Cu(111): Strength and Orientation of the Electric Dipole Moment

In order to investigate the orientational ordering of molecular dipoles and the associated electronic properties, we studied the adsorption of chlorogallium phthalocyanine molecules (GaClPc, Pc=C_32N_8H_16) on Cu(111) using the X-ray standing wave technique, photoelectron spectroscopy, and quantum chemical calculations. We find that for sub-monolayer coverages on Cu(111) the majority of GaClPc molecules adsorb in a 'Cl-down' configuration by forming a covalent bond to the substrate. For bilayer coverages the XSW data indicate a co-existence of the 'Cl-down' and 'Cl-up' configuration on the substrate. The structural details established for both cases and supplementary calculations of the adsorbate system allow us to analyze the observed change of the work function.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let

Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine

The electronic structure of ZnPc, from sub-monolayers to thick films, on bare and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM). Our results suggest that at low coverage ZnPc lies almost parallel to the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt attraction, leading to an inhomogeneous charge distribution within the molecule and charge transfer to the molecule. ZnPc does not form a complete monolayer on the Pt surface, due to a surface-mediated intermolecular repulsion. At higher coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate interaction. Our photoemission results illustrate that ZnPc is practically decoupled from Pt, already from the second layer. Pre-deposition of iodine on Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in contact with Pt(111)-I $\left(\sqrt{3}\times\sqrt{3}\right)$ or Pt(111)-I $\left(\sqrt{7}\times\sqrt{7}\right)$, and a more homogeneous charge distribution and charge transfer at the interface. On increased ZnPc thickness iodine is dissolved in the organic film where it acts as an electron acceptor dopant.Comment: 12 pages, 9 figure