CIS Films Research Articles

Characterization of CuInSe2 Thin Films by Photoluminescence Measurements

PL measurement has been clearly demonstrated to be an effective technique not only to evaluate the quality of CIS-based thin films but also to investigate the CIS formation process during the selenization stage. The studies investigating the dependence of the PL spectrum on the excitation intensity and the effect of post-annealing in air clarified that the PL spectrum of CIS thin films was dominated by a donor-acceptor (D-A) pair emission and even in a 5 min post-annealing, the PL peak of as-deposited CIS films drastically shifted from 0.93 eV (1340 nm) to about 0.89 eV (1400 nm).

Vibrational properties of Li-doped polyacetylene

Raman experiments on (CH) x chemically doped with Li are reported. A very fast cis-trans isomerization is observed upon doping. Raman spectra of Li-doped cis or trans films show special features characteristic of short trans segments which remain undoped. Further, an additional Raman band at ≌ 1570 cm −1 is reported, as in the p-type doping case, associated with doped parts of the polymer. A possible interpretation with intercalated domains is suggested.

Defect states in polyacetylene: A photoacoustic and diffuse reflectance study

We present a combined photoacoustic spectroscopy (PAS) and polarized diffuse reflectance (PDR) study of relatively thick freestanding cis and trans polyacetylene films in the visible-near IR regime. Both techniques are suitable for measuring low absorption coefficients in solids. The PAS signal for the cis isomer is saturated in the region of the strong interband transition. There is no absorption in the near IR except for a vibrational overtone band at 0.74 eV. Thermal isomerization leads to a very broad, featureless absorption band in the near IR consistent with a broad distribution of defect states in the bandgap of trans-polyacetylene. Polarized diffuse reflectance spectra also show a higher absorption in the near IR for the trans isomer. Upon doping with oxygen, an absorption peak grows with time with a maximum at 0.67 eV and a characteristic asymmetric line shape consistent with soliton absorption and similar to what has been observed in the absorption spectra of thin acceptor-doped (CH)x films. Our PDR results suggest an absorption coefficient of the order of 100 cm−1 for the defect absorption in undoped trans-polyacetylene.

Structural study of thecis-to-transthermal isomerization in polyacetylene

We have studied the variations of Debye-Scherrer x-ray synchrotron radiation patterns of polyacetylene with cis-to-trans isomerization. At each stage of the isomerization we observe only one series of x-ray lines at positions intermediate between those of pure cis and pure trans films. In addition, the crystallinity and lateral crystallite size do not change appreciably during isomerization. The observations lead us to conclude that the isomerization process is homogeneous without clustering of trans regions within the cis host lattice.

Crystalline features in AsF5-doped polyacetylene

Neutron diffraction studies are reported on cis and trans-polyacetylene films in both doped and undoped conditions. (AIP)

Synthesis and characterization of bromine substituted polyacetylene, [CH1-yBry]x

Abstract When ca. 85% cis films of the semiconducting polymer, polyacetylene, (CH)x, are first doped with bromine and then partly dehydrobrominated at 150°C, substitution of II by Br occurs to yield new semiconducting polymers of general composition [CH1-uBry]x, where y=0.003-0.23. These films have been studied using electron paramagnetic resonance (EPR), dynamic nuclear polarization (DNP), and Raman spectroscopic techniques. EPR results indicate that with an increase in bromine substitution, the linewidth (ΔHpp), g-value, and homogeneity of the samples increase. This is consistent with DNP results which suggest a decrease in the diffusion coefficient of unpaired spins as the bromine substitution level increases. Raman results are consistent with bromine substitution and indicate that essentially no change in conjugation length occurs when H is substituted by Br.

‘Organic metals.’ Synthesis of a new type of organic metal derived from polyacetylene, (CH)x

When ca. 85%cis films of the semiconducting polymer, polyacetylene, (CH)x, are doped with bromine to compositions such as [CHBry]x(y=ca. 0·15–0·35) and then partly dehydrobrominated at 150°C, they yield new semi-conducting polymers such as [CH0·85Br0·11]x which can then be doped with I2 or AsF5 to yield new highly conducting organic metals such as [CH0·89Br0·09I0·12]x and [CH0·82Br0·13(AsF5)0·12]x, respectively.

‘Organic metals’. New classes of p-type dopants for converting polyacetylene, (CH)xinto the ‘metallic’ state

When ca. 85%cis films of the semiconducting polymer, ‘polyacetylene,’(CH)x, are treated with H2SO4, HClO4, (NO2)(SbF6), (NO)(SbCl6), and (NO2)(BF4) two new classes of dopants are introduced to give golden, flexible films exhibiting high conductivities characteristic of the metallic state.