In recent years, PPDT2FBT is getting researchers’ attention due to its applications in solar cells and optoelectronic devices. Although the main applications of this material are based on the optical properties. However, the optical dispersion of this material has not been studied yet over the UV and visible spectral range. We report the optical properties of PPDT2FBT for the wavelength range of 300 nm to 900 nm using a variable angle spectroscopic ellipsometry (SE). The refractive index (n) and extinction coefficient (k) of spin coated PPDT2FBT thin films were determined at room temperature. Glass of known optical properties was used as the substrates for convenience. To build an optical model the surface morphology was studied using atomic force microscopy (AFM). Then an optical model was developed based on the extracted properties. The optical properties were found to be consistent with the UV-Vis data. The bandgap was estimated from the absorption properties. Finally, the developed ellipsometry model was used for thickness measurement of PPDT2FBT thin films. The measured data agreed well with the data collected using other direct thickness measurement techniques of the same thin film. This developed model can be useful for designing effective optoelectronic devices as well as measuring the thickness of thin films in a nondestructive way.
Methylammonium lead iodide (CH3NH3PbI3 or MAPI) is an organohalide lead perovskite, a promising material for optoelectronic application, e.g. in solar cells and photodetectors. It has a number of advantages over more traditional photovoltaics materials such as CIGS, GaAs, and even silicon due to facile solution processing, direct bandgap, high optical absorption, sufficiently high, balanced carrier mobilities, shallow trap defects and low-cost synthesis. At present moment there are number of article which reported measurement of second-harmonic generation in MAPI single crystals and presented contradictory results demonstrating the presence or absence of second-harmonic signal from MAPI. In this work, the second-harmonic generation (SHG) is observed in MAPI thin film that can be used as a base of high efficient solar sell.
The SHG intensity from MAPI is measured to be at least three orders of magnitude more than one from substrate and encapsulation glasses. The MAPI nonlinear second-order susceptibility is estimated as compared to reference sample of y-cut quartz. In case of bulk contribution, the MAPI second-order susceptibility of 10-15 m/V is achieved.
The polarization of SHG signal is experimentally studied in MAPI samples. The fraction of linearly polarized SHG signal is different for p- and s-polarization of fundamental wave and increases in case of p-polarized pump. The large non-polarized background of SHG signal is partly corresponded to SHG hyper-Rayleigh scattering. The hyper-Rayleigh scattering angle is experimentally estimated using the diaphragm behind the collimating objective lens and found to be less then 11 degrees.
Silicon nanowires were synthesized on silicon substrate by depositing Ag and Cu particles using electroless
metal deposition (EMD) technique followed by HF/Fe(NO3)3 solution based etching at room temperature.
Structural and optical characterizations were done on synthesized nanowires. Nanowires of diameter 45 nm to
200 nm having length 2 μm to 4 μm were evident from the scanning electron microscope (SEM) images with
maximum aspect ratio 100. Optical absorption study using 400 nm to 1100 nm wavelength by UV/VIS
spectrophotometer revealed that synthesized structures absorbed up to 78% of incident radiation in the
wavelength range 400 nm to 820 nm, which is much better than that of bulk silicon as they absorbed maximum
67% of the radiation. This observation supports that the material synthesized could be a potential candidate for
efficient photovoltaic solar cell and other optoelectronic devices.