TY  - JOUR
A1  - Schubert, Marcel
A1  - Yin, Chunhong
A1  - Castellani, Mauro
A1  - Bange, Sebastian
A1  - Tam, Teck Lip
A1  - Sellinger, Alan
A1  - Hoerhold, Hans-Heinrich
A1  - Kietzke, Thomas
A1  - Neher, Dieter
T1  - Heterojunction topology versus fill factor correlations in novel hybrid small-molecular/polymeric solar cells
N2  - The authors present organic photovoltaic (OPV) devices comprising a small molecule electron acceptor based on 2- vinyl-4,5-dicyanoimidazole (Vinazene (TM)) and a soluble poly(p-phenylenevinylene) derivative as the electron donor. A strong dependence of the fill factor (FF) and the external quantum efficiency [incident photons converted to electrons (IPCE)] on the heterojunction topology is observed. As-prepared blends provided relatively low FF and IPCE values of 26% and 4.5%, respectively, which are attributed to significant recombination of geminate pairs and free carriers in a highly intermixed blend morphology. Going to an all-solution processed bilayer device, the FF and IPCE dramatically increased to 43% and 27%, respectively. The FF increases further to 57% in devices comprising thermally deposited Vinazene layers where there is virtually no interpenetration at the donor/acceptor interface. This very high FF is comparable to values reported for OPV using fullerenes as the electron acceptor. Furthermore, the rather low electron affinity of Vinazene compound near 3.5 eV enabled a technologically important open circuit voltage (V-oc) of 1.0 V.
Y1  - 2009
UR  - http://jcp.aip.org/
U6  - https://doi.org/10.1063/1.3077007
SN  - 0021-9606
ER  - 
TY  - JOUR
A1  - Inal, Sahika
A1  - Castellani, Mauro
A1  - Sellinger, Alan
A1  - Neher, Dieter
T1  - Relationship of photophysical properties and the device performance of novel hybrid small-molecular/polymeric solar cells
N2  - We investigate solar cells comprised of a vinazene derivative (HV-BT) as the electron acceptor and the well- known polymer poly(3-hexylthiophene) as the electron donor. In the as-prepared blend, most of the excited state species, including the excimers on HV-BT, are quenched at the heterojunction. Although the photophysical properties of the blends change upon annealing, the blend solar cells largely remain uninfluenced by such treatments. A significant improvement is, however, observed when inducing phase separation at a longer length scale, for example, in solution-processed bilayer devices. Hereby, both the fill factor (FF) and the open circuit voltage are considerably increased, pointing to the importance of the heterojunction topology and the layer composition at the charge extracting contacts. An optimized device exhibits a power conversion efficiency of close to 1%.
Y1  - 2009
UR  - http://www3.interscience.wiley.com/cgi-bin/jhome/10003270
U6  - https://doi.org/10.1002/marc.200900221
SN  - 1022-1336
ER  - 
TY  - JOUR
A1  - Castellani, Mauro
A1  - Salzmann, Ingo
A1  - Bugnon, Philippe
A1  - Yu, Shuwen
A1  - Oehzelt, Martin
A1  - Koch, Norbert
T1  - Structural and electronic implications for carrier injection into organic semiconductors
N2  - We report on the structural and electronic interface formation between ITO (indium-tin-oxide) and prototypical organic small molecular semiconductors, i.e., CuPc (copper phthalocyanine) and alpha-NPD (N,N'-di(naphtalen-1-yl)- N,N'-diphenyl-benzidine). In particular, the effects of in situ oxygen plasma pretreatment of the ITO surface on interface properties are examined in detail: Organic layer-thickness dependent Kelvin probe measurements revealed a good alignment of the ITO work function and the highest occupied electronic level of the organic material in all samples. In contrast, the electrical properties of hole-only and bipolar organic diodes depend strongly on the treatment of ITO prior to organic deposition. This dependence is more pronounced for diodes made of polycrystalline CuPc than for those of amorphous alpha-NPD layers. X-ray diffraction and atomic force microscopic (AFM) investigations of CuPc nucleation and growth evidenced a more pronounced texture of the polycrystalline film structure on the ITO substrate that was oxygen plasma treated prior to organic layer deposition. These findings suggest that the anisotropic electrical properties of CuPc crystallites, and their orientation with respect to the substrate, strongly affect the charge carrier injection and transport properties at the anode interface.
Y1  - 2009
UR  - http://www.springerlink.com/content/100501
U6  - https://doi.org/10.1007/s00339-009-5336-6
SN  - 0947-8396
ER  -