Ajay Singh Verma

Buffer layer selection for CuIn1 − x Ga x Se2 based thin film solar cells

In this work, device modeling and simulation studies have been carried out with a variety of buffer layers over CIGS absorption layer. The band diagram, electric field variation and I/V curves are analyzed and device performance parameters i.e. efficiency, open circuit voltage, short circuit current, quantum efficiency are calculated. The efficiency of CIGS solar cell with ZnSe buffer layer is found comparable with that of CdS layer. The highest short circuit current is found for solar cell with ZnSe buffer layer, whereas the ZnS/CIGS heterojunction provides the highest quantum efficiency in the structures considered. The device physics is discussed and the effect of thickness of buffer layers and absorption layer is studied in order to find a more efficient and stable solar cell.

INHERENT PROPERTIES OF TERNARY

In this paper we have evaluated inherent properties (i.e., heat of formation and cohesive energy) for chalcopyrite structured solids. We have presented two expressions relating the heat of formation and cohesive energy for and semiconductors with the product of ionic charge (ZAZBZC) and nearest neighbor distance (d in A). The heat of formation and cohesive energy of these solids exhibit a linear relationship when plotted on a log–log scale against the nearest neighbor distance, but fall on different straight lines according to the product of ionic charge of the compounds. We have applied the modified relations on these solids and found a better agreement with experimental data as compared to the values evaluated by previous researchers so far. The results for heat of formation differ from experimental values by the following amounts: ZnSiP2 — 4.8%, ZnSnP2 — 0.4%, ZnSiAs2 — 0.7%, ZnGeAs2 — 2.6%, ZnSnAs2 — 1.2%, CdGeP2 — 3.8%, CuGaSe2 — 0.3% and AgInSe2 — 5% and the results for cohesive energy differ from experimental values by the following amounts: ZnSiP2 — 0.3%, ZnSnAs2 — 1.5%, CuGaSe2 — 3.7%, CuGaTe2 — 2%, CuInTe2 — 2.7%, AgGaTe2 — 0.7%, AgInSe2 — 3%, AgInTe2 — 3%.

(A^{N}B^{2+N}C_{2}^{7-N})

We have performed ab initio calculations for the structural, electronic, optical, elastic and thermal properties of CuGaTe2. In this study, we used an accurate full potential linearized augmented plane wave (FP-LAPW) method to find the equilibrium structural parameters and to compute the full elastic tensors. We report electronic and optical properties with the recently developed density functional of Tran and Blaha. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, were calculated for photon energies up to 30 eV. The thermodynamical properties such as Debye temperature, entropy and Gruneisen parameter, bulk modulus and hardness were calculated employing the quasi-harmonic Debye model at different temperatures (0–1000 K) and pressures (0–8 GPa) and the silent results were interpreted. Most of the investigated parameters are reported for the first time.

TETRAHEDRAL SEMICONDUCTORS

In this paper, we present the expressions relating the inter atomic force constants like as bond-stretching force constant (α in N/m) and bond-bending force constant (β in N/m) for the binary (zinc blende structure) and ternary (chalcopyrite structure) semiconductors with the product of ionic charges (PIC) and crystal ionicity (fi). Interatomic force constants of these compounds exhibit a linear relationship; when plot a graph between Interatomic force constants and the nearest neighbor distance d (Å) with crystal ionicity (fi), but fall on different straight lines according to the product of ionic charges of these compounds. A fairly good agreement has been found between the observed and calculated values of the α and β for binary and ternary tetrahedral semiconductors.

Ab initio studies of structural, electronic, optical, elastic and thermal properties of CuGaTe2

The authors have performed, the modeling of thin film CuGaS2 based solar cell with ZnTe buffer layer. The efficiency of the cell, short circuit current density and fill factor are calculated. In addition the effect of thickness of absorption layer over performance parameters of the cell is studied and it is found that maximum efficiency of the cell is achieved for 2000 nm thick absorption layer.

Inter atomic force constants of binary and ternary tetrahedral semiconductors

The structural, electronic and thermal properties of ZnSiX2 (X=P, As) have been calculated using the full-potential linearized-augmented plane wave (FP-LAPW) method. The exchange and correlation potential is treated by an orbital independent modified Becke-Johnson (mBJ) potential as coupled with Generalized Gradient Approximation (GGA) for these calculations. The ground state properties such as lattice constants, bulk modulus and its pressure derivative are in good agreement with numerous experimental and theoretical data. The quasi harmonic Debye model, using a set of total energy versus volume calculations obtained with FP-LAPW method is applied to predict the thermal properties (thermal expansion coefficient (α), vibrational contribution to the volume and pressure constant heat capacities (Cv and Cp), isothermal and adiabatic bulk modulus (B and Bs), Debye temperature (θD) and Gruneisen parameter (γ). Further the temperature and pressure affects on the lattice parameter, bulk modulus and thermal expans...

Modeling and analysis of CuGaS2 thin-film solar cell

The structural, electronic, optical and elastic properties of zinc-blende compounds (ZnX, X = S, Se and Te) have been investigated using the full-potential augmented plane wave plus local orbitals method within density functional theory. The generalized gradient approximation (GGA) formalism is used for the exchange correlation energy to calculate the bulk properties including lattice constant, bulk modulus and its pressure derivative. Electronic band gap, complex refractive index and elastic constants (C11, C12 and C44) are also evaluated. Our results are in reasonable agreement with the available theoretical and experimental data.