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Nano-polycrystalline thin films of CuIn1-xAlxSe2 (CIAS) chalcopyrite material are re-grown on annealing the 700 nm thick Cu/In/Al/Se stack at temperatures ranging from 523 to 623 K. The stack is obtained at room temperature by sequentially evaporated layer deposition (SELD) technique. The grown films show a tetragonal crystal system of CIAS having unit cell parameters a; b = 5.781(5) Å, c = 11.593 (7) Å, with cell volume (V) = 387.523(4) Å3. The micrographs of the films show grains of spherical and cylindrical shapes. Raman spectra of the layers indicate A1 mode at 180.72(7) cm−1, which confirms the CIAS phase. The thin film's energy dispersive X-ray analysis (EDAX) establishes CuIn0.63Al0.37Se2 stoichiometry at 523 K. The direct allowed bandgap (Eg) value varies between 1.35 and 1.50 eV with a change in TA from 523 to 623 K; the values are near the optimum PV cell. The grown thin film samples exhibit absorption coefficient (α) ≥ 1 × 105 cm−1. The solar cell structure of FTO/p-CIAS/n-CdS/In exhibits a photovoltaic (PV) response.

Thin films of nanocrystalline selenium (Se) of different thicknesses were grown on annealing from 323 to 398 K. The crystallinity of the layers increased with annealing temperatures (TA). The temperature thickness correlations were established. The layers exhibited spherical-shaped particles at higher annealing temperatures. The grown layers possess hexagonal crystal system with space group P3121(152); it shows prominent planes along the a-axis. The bandgap (Eg) decreases from 2.18 to 1.94 eV, 2.12 to 1.82 eV, and 2.13 to 1.84 eV with changes in TA of 700, 270, and 150 nm thick layers, respectively. The high absorption coefficient (α) values ∼ 1 × 105 cm−1 observed in all films makes it suitable as an absorber layer in a solar cell structure and an optical sensor. The FTO/p-Se/n-CdS/In heterojunction diodes provide zero-bias barrier height (фbo) of 0.788(7) eV. The open circuit voltage (Voc) of FTO/p-Se (150 nm)/n-CdS(200 nm)/In a photovoltaic cell was observed to be 55 mV.

Two-dimensional (2D) lead halide perovskites have garnered increasing interest due to their high photoluminescence quantum yields and tunable luminescence characters, making them excellent materials in light-emitting, especially for white-light emission. In contrast to their 3D analogues, they are formed by inserting large organic cations between the anionic layers of lead halide octahedra. Herein, we designed and prepared AVA2PbClxBr4-x (x = 0, 1, 2, 3, 4) alloy perovskites, in which AVA (5-aminovaleric acid) was used as an organic cation to separate the layers of chlorine-substituted lead bromide 2D perovskite, in order to identify the role of Cl substitution in tuning the bandgap and luminescence characters of the 2D AVA2PbBr4 perovskite. X-ray diffraction measurements revealed achievement of single-phase thin films of AVA2PbClxBr4-x perovskites with a (001) orientation. With increasing Cl/Br ratio from 0 to 1, the lattice constant c was found to decrease from 1.672 nm to 1.597 nm following c(x) = 1.674 – 0.076x, while the bandgap increased from 3.11 eV to 3.76 eV as approximated with Eg(x) = 3.08 + 0.62x. Correspondingly, the alloy luminescence character evolved from narrow-band blue-violet to broadband white-light emission, which was attributed to transformation from free-exciton to self-trapped-exciton emission with increasing octahedral distortion caused by Cl substitution. Based on an alloy system with continuously varying content designed for the first time, the work highlighted the role of Cl incorporation in changing the crystal lattice structure, and tuning bandgap as well as the light emission characters in 2D lead halide perovskites.

Successful integration of perovskite cell with silicon cell to form a tandem solar device has shown tremendous potential for outperforming the state-of-the-art single junction silicon devices. This tandem approach has enabled high efficiencies up to 29% within a short period of time and one can find sufficient work and various strategies being applied to enhance the efficiency in these devices. At this point in time, a compilation of all these studies, with a critical review and perspectives is extremely relevant and essential. With this motivation the present review has been brought out, with all achievements attained so far by optimizing various components namely the electron/hole transport layer and absorber layer, functional layers in bottom cell, transparent contacts, deposition techniques and the innovative light management tactics used. The review also outlines the solutions proposed by various researchers to overcome the challenges that restrict the efficiency of tandem strategy in three distinct configurations, namely, monolithic (2T), four terminal (4T) and three terminal (3T) configurations. Finally, the perspectives provide real insights into choosing suitable materials, techniques and methods and achieve efficiencies near and beyond Shockley Queisser limit, thus spiking high hopes that this device would be the dominant energy conversion device in future.

The antiperovskites based on metal halides have emerged as potential materials for advanced photovoltaic and electronic device applications. But the wide bandgap of non-toxic CsSnCl3 reduces its photovoltaic efficiency. Here, we report the change of electronic structure of CsSnCl3 at different pressure by using GGA-rPBE and GGA-PBEsol functionals and the GW method. We have shown that the prediction of electronic structure transition (semiconducting to metallic state) strongly depends on the exchange-correlation and the GW method gives the most reasonable values of the bandgap under pressure. The pressure increases the electronic density of states close to the Fermi level by pushing the valence electrons upward and thus, reduces the bandgap linearly. Afterward, we have also investigated the influence of pressure on absorption coefficient, and mechanical properties meticulously. Although the pressure shifts the absorption peak to lower photon energies, the absorption coefficient is slightly improved.

The formation of an AlZnN alloy was investigated as a route to tune the bandgap of Zn3N2. A significant shift of the bandgap was observed in the deposited films, increasing from 1.4 eV for Zn3N2 to 2.8 eV for AlZnN alloys with an AlN fraction of × = 0.19. The refractive index followed a similar trend, approaching that of AlN. The charge carrier density of AlZnN samples was significantly reduced reaching values in the order of 1016 cm−3.