Mixed crystalline films of co-evaporated hydrogen- and fluorine-terminated phthalocyanines and their application in photovoltaic devices

Abstract

Blends of organic electron and hole conductive materials are widely used for ambipolar charge carrier transport and photovoltaic cells. An obvious choice for donor-acceptor blends are organic semiconducting materials in their hydrogenated and fluorinated form, since they combine potentially suitable electronic properties with structural compatibility of the two constituents. This study focuses on the structural, optical, and electrical properties of blends using hydrogenated copper-phthalocyanine (H 16 CuPc) in combination with its perfluorinated version (F 16 CuPc). Using X-ray scattering, scanning force microscopy and optical absorption measurements we show that mixed crystalline films are obtained by co-evaporation of the two materials. Electrical transport measurements reveal a profound reduction of the current for bipolar charge injection in mixed films. We discuss the formation of self-trapped charge-transfer excitons as possible explanation for this unexpected behaviour, which impedes the usability of this system in photovoltaic cells.

Low-energy electron transmission for the analysis of the interface barrier formation and the density of the unoccupied electronic states in the ultra-thin layers of fluorinated copper-phthalocyanine

“…3b). The decrease of the Evac level corresponds to the negative charge (electron) transfer from the CuPc overlayer to the F 16 -CuPc underlayer, which corresponds well to the results of the photoemission studies of these films [6,18,20] as well as to the studies of the work function changes upon the introduction of polar substituents into the small organic molecules [12]. The mostly rapid changes of the Evac -E F values occur within the 2 nm of the CuPc deposit while the smaller changes are still observed upon the deposit thickness increase even above 5 nm corresponding to the (Fig.…”

“…The ionization potential of the F 16 -CuPc films was determined as about 6 eV, which is approximately 1.1 eV higher than the ionization potential of the unsubstituted CuPc. There has been shown that CuPc molecules act as electron donors relatively to the silicon, titanium and zinc oxide surfaces [21] while electron acceptor behavior is expected from F 16 -CuPc [6,20]. In this paper the authors present the TCS results on the band alignment and on DOUS at the interface of the CuPc and F 16 -CuPc ultra-thin layers.…”

“…A number of surface science studies have been devoted to the films of copper-phthalocyanine (CuPc) and fluorinated copper-phthalocyanine (F 16 -CuPc) [6,[18][19][20]. The ionization potential of the F 16 -CuPc films was determined as about 6 eV, which is approximately 1.1 eV higher than the ionization potential of the unsubstituted CuPc.…”

Efficient Organic Tandem Solar Cells based on Small Molecules

“…[ 29 ] Higher fl uorinated phthalocyanine derivatives can even be used as acceptor molecules in organic solar cells. [ 30 ] The absorption features of F4-ZnPc in mixed layers with C 60 are comparable to ZnPc, exhibiting strong absorbance in the red part of the spectrum peaking at 630 nm and extending to above 800 nm.…”

Organic–Organic Heterostructures: Concepts and Applications

“…[232][233][234] For other work on organic-organic heterostructures combining structural as well as spectroscopic characterization with transport or other device performance parameters we refer to refs. [13,71,99,235] and references therein.…”