IR@NPL
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Interaction of oxygen and carbon impurities with the multiphonon infrared absorption bands of Silicon at low temperatures
No full textInfrared absorptance measurements of polycrystalline silicon and single crystals of silicon having oxygen and carbon impurities were carried out at low temperatures in the wavelength range of multiphonon infrared absorption of silicon. Peak absorptance and frequencies were measured at temperatures from 10 to 130 K at intervals of 10 K. Absorptance-temperature curves were plotted for multiphonon bands and impurity bands. It has been observed that the three phonon band [2 TO (Γ) + TA (L)] exhibits a resonance-like behaviour with the anti-stretching mode of Si-O at low temperatures
Multiphonon infrared absorption in silicon
No full textInvestigations have been carried out on silicon crystals, grown by float zone (FZ) and Czochralski (CZ) methods, of infrared absorption bands using a Fourier transform infrared spectrophotometer. Multiphonon bands are identified in the light of recent theoretical calculations based on the total energy of silicon crystal lattice. Theoretical results of Ihm et al.(1) and Yin and Cohen(2,3) are found to be in good agreement with the experimental observations of multiphonon infrared bands
Lateral structure of domains in ferroelectric TGS
No full textLaser probe technique1,2 has been used to study the lateral structure of domains in ferroelectric triglycine sulfate. No regular pattern of domains exists along the polar axis. Regions of high pyroelectricsignal are observed and attributed to microscopic reversible domains
Organic tandem solar cells with 18.6% efficiency
No full textTandem organic photovoltaic (TOPV) cell is one of the technologies to harvest more solar power by staking two or more OPV devices on top of each other. Recently, the highest power conversion efficiency (PCE) ever achieved was 17.3%. Herein, this paper simulates the response of 676 different TOPV devices that consists front and back OPV cells. For this purpose, this paper uses the best 26 single-cell OPV devices to form the TOPV front and back cells combinations. The results show that there are some new TOPVs that can exceed 17.3% efficiency limit for TOPV. Also, in this work thickness optimization was performed for these new TOPV devices with an objective of efficiency maximization. As a result, using PBDTS-TDZ: ITIC in the front cells and PTB7-Th: O6T-4F:PC71BM in the back cell gives 18.6% efficiency. Likewise, the TOPV of PBDB-T-2F:TfIF-4FIC in the front cell with PTB7Th:O6T-4F:PC71BM in the back cell gives 18.06% efficiency
Characteristics of a conducting organic diode with finite (nonzero) Schottky barrier
No full textWhen the transport and Poisson equations are integrated a constant of integration C should be used. If the Schottky barrier (phi(B)) between metal electrode and organic semiconductor is zero, the injected carrier density at the contact is equal to that at the Fermi surface of the metal and can be taken as infinity to a good approximation. In this case the constant of integration C becomes zero. But for most cathodes and anodes used in organic devices the Schottky barriers are not zero. In these cases the constant C comes out to be A[J/P(0)(m)], where the constant A depends on material parameters, m is a constant more than 1, J is the current density, and P(0)proportional to exp(-phi(B)/kT) is the injected carrier density. Even for a small value of the Schottky barrier phi(B)=0.12 eV, P(0) is reduced by two orders of magnitude. For this or smaller value of P(0), C plays an important role in determining the J-V characteristics. We report a theory of J-V characteristics for finite (nonzero) Schottky barriers. Even for small values of the Schottky barrier the results are strikingly different from the conventional theory based on zero barrier. As the barrier increases the deviation from the conventional theory becomes large. For very large values of C, J-V characteristics become Ohmic. We have fabricated ITO/PEDOT:PSS/MEH-PPV/Au diode and measured their J-V characteristics. The theory given in this paper agrees with the experimental data at different temperatures and different sample thicknesses