High efficiency near-infrared (NIR) absorbing solar cells based on lead phthalocyanine (PbPc) are reported using copper
iodide (CuI) as a templating layer to control the crystal structure of PbPc. Devices with CuI inserted between the ITO
and PbPc layers exhibit a two times enhancement of the JSC compared to the case in the absence of the CuI layer. This is
due to the increase of crystallinity in the molecules grown on the CuI templating layer, which is investigated via an x-ray
diffraction study. Moreover, fill factor is also enhanced to 0.63 from 0.57 due to low series resistance although the
additional CuI layer is inserted between the ITO and the PbPc layer. As a result, the corrected power conversion
efficiency of 2.5% was obtained, which is the highest one reported up to now among the PbPc based solar cells.
ZnPc and CuPc molecules stacked similar way in the film, but showed different growth modes in thermal evaporation.
The distribution of CuPc crystals did not change by the film thickness, whereas the distribution of ZnPc became random
as the increase of the film thickness. The disc type nanograins of CuPc were quite regularly distributed at the initial
growth regime and the regular distribution of nanograins was kept during the film growth. On the other hand, ZnPc
consisted in ellipsoid shaped nanograins and the distribution of nanograins was not regular in the initial growth regime.
The irregular distribution of nanograins changed to the regular mode at the later growth regime by showing structure
factor in GISAXS measurement. The different initial nanograin distribution in ZnPc and CuPc was related to the
different nanostructure in the mixed layer with C60 to form the bulk heterojunction.
Real time grazing incidence small angle x-ray scattering (GI-SAXS) and x-ray reflectivity measurements were conducted
in order to investigate the thermal evolution of the nano-grain structure and surface of 5nm thick Copper(II)
Phthalocyanine (CuPc) films. The evolution was strongly influenced by the surface energy of silicon substrate. On the
low surface energy (hydrophobic) Si substrate, CuPc nano-grains are randomly distributed and the crystal size did not
increase in size upon thermal annealing. Thermal annealing induced a more random distribution of nano-grains with an
increase in roughness, and large islands formed by the coalescence of small grains. On the high surface energy
(hydrophilic) Si substrate, CuPc film consisted of disk shaped nano-grains of two different sizes. The larger grains
showed lateral crystal growth and planarization by thermal annealing, while the smaller grains did not increase in size.
Large clusters were observed at high temperature, which were derived by large grains. The different thermal evolution
models of CuPc films based on GI-SAXS analysis are consistent with the different temperature behavior of the hole
mobilities of organic field-effect transistor (OFET) devices fabricated on both surfaces.
The Al electrode on P3HT:PCBM blended thin films modified the nano structure of P3HT crystals during thermal
annealing. The presence of an Al layer induced less preferred distribution of P3HT crystals after thermal annealing. In
the surface region, the lateral growth of amorphous like (0.7 nm thick in [010] direction) face-on P3HT crystals was also
affected by the inter diffusion of Al atoms into the active layer during thermal annealing in the presence of the Al layer.
The inter diffusion of Al atoms produced an intermediate layer between the electrode and the active layer. By the real
time measurement using synchrotron x-rays, we could confirm interfacial changes during annealing process. To
understand the relation of structures and the device performance, we fabricated devices using pre and post annealing
processes. The J-V characteristics show that more randomly distributed P3HT crystals are more advantageous to form
the interpenetrating networks in the active layer. The short circuit current seems to be affected by nano structure of P3HT
crystals in the bulk region, while the series resistance is more affected by the interfacial properties between the electrode
and the active layer.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.