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Objective: Herein, we report the effect of variation of hydrogen flow rate on the properties of Si:H films synthesized using PE-CVD method. Raman spectroscopy analysis show an increase in crystalline volume fraction and crystallite size implying that hydrogen flow in PE-CVD promotes the growth of crystallinity in nc-Si:H films with an expense of a reduction in deposition rate. Methods: FTIR spectroscopy analysis indicates that hydrogen content in the film increases with an increase in hydrogen flow rate and hydrogen is predominantly incorporated in Si-H2 and (Si-H2)n bonding configuration. The optical band gap determined using E04 method and Tauc method (ETauc) show an increasing trend with an increase in hydrogen flow rate and E04 is found higher than ETauc over the entire range of hydrogen flow rate studied. Results and Conclusion: We found that the defect density and Urbach energy increases with an increase in hydrogen flow rate. Photosensitivity (σPhoto /σDark) decreases from ~103 to ~1 when hydrogen flow rate is increased from 30 sccm to 100 sccm and can be attributed to amorphous-to-nanocrystallization transition in Si:H films. The results obtained from the present study demonstrated that hydrogen flow rate is an important deposition parameter in PECVD to synthesize nc-Si:H films.

Objective: Phosphorus doped hydrogenated nano-crystalline silicon (nc-Si:H) thin films were synthesized by catalytic chemical vapor deposition (Cat-CVD) method. Methods: The effect of deposition pressure on opto-electronic and structural properties was studied using various analysis techniques such as low angle XRD analysis, FTIR spectroscopy, Raman spectroscopy, UV-Visible spectroscopy, dark conductivity, etc. Results: From low angle XRD and Raman spectroscopy analysis, it is observed that an increase in deposition pressure causes Si:H films to transform and transit from amorphous to the crystalline phase. At optimized deposition pressure (300 mTorr), phosphorous doped nc- Si:H films having a crystallite size of ∼29 nm and crystalline volume fraction of ∼58% along with high deposition rate (∼29.7 Å/s) have been obtained. The band gap was found to be ∼1.98 eV and hydrogen content was as low as (∼1.72 at. %) for these films. Conclusion: The deposited films can be useful as an n-type layer for Si:H based p-i-n, tandem and c-Si hetero-junction solar cells.

Bismuth halide perovskites have been proposed as a non-toxic and chemically stable alternative to lead halide perovskites. Despite being highly stable, the devices based on bismuth perovskites have not been able to compete with the lead counterparts in terms of its efficiencies. The compounds that have been extensively studied i.e. Cs3Bi2I9 and MA3Bi2I9 form 0D (dimer) structures that possess wide indirect band gaps and poor charge transport properties which hinders the performance of devices based on these materials. Theoretical studies have revealed that replacing bigger A cation like Cs/MA by smaller cation like potassium (K) could favor the formation of layered 2D structures rather than 0D structure. We have synthesized inorganic K3Bi2I9 perovskite thin films by facile one-step spin coating method and investigated its structural, optical and morphological properties. The fabricated films showed strong absorption in UV and visible region of solar spectrum and possess optical band gap ∼2 eV. On comparison with the Cs analogue, it is observed that reduction in the cation size (Cs to K) hardly changes the band gap of K3Bi2I9 films which implies that the band gap of A3Bi2I9 perovskite is insensitive to A-site variation. Films deposited on preheated substrates showed comparatively good coverage without voids on the film surface. Our preliminary studies on this material showed that the films deposited by one-step solution method favored 0D structure rather than the expected 2D layered structure.

In present study, CZTS films were fabricated using 2 different processes and their properties have been compared. The first is a 2-stage process which includes deposition of CZT followed by sulfurization and the second is a 3-stage process which includes deposition of identical CZT, soft annealing (pre-heating) and sulfurization. Structural, morphological, optical and compositional properties of CZTS films are investigated by XRD, Raman spectroscopy, FE-SEM, UV–Visible spectroscopy, EDS and photoresponse measurements. Structural analysis revealed that films prepared by both processes have polycrystalline kesterite-CZTS structure and exhibit prefered orientation along (1 1 2) direction. It has been observed that soft annealing temperature in 3-stage process significantly improve the crystal quality of CZTS films. Surface morphology of films sulfurized at 550 °C shows a uniform and compact micrograin (∼0.31 µm) without cracks. The soft annealing temperature significantly improves micrograin size (∼0.49 µm) and compactness of CZTS films. UV–Visible spectroscopy showed that the band gap of all CZTS films is in optimal range. The CZTS films fabricated by 3-stage process, exhibits high photocurrent response under intermittent visible-light irradiation, implying that they can useful as an absorber layer in solar cells.

Zinc oxide nano-sheets (ZNS) loaded with Zeolitic Imidazole Framework 8 (ZIF8) nanocrystals, i.e. (ZNS@ZIF8) thin films, were successfully synthesized using electrodeposition and facile chemical bath deposition (CBD) for photoelectrochemical (PEC) splitting of water. The formation of ZNS nano-sheets and ZIF8 nano-crystals has been confirmed by field emission scanning electron microscopy (FE-SEM), low angle X-ray diffraction (XRD), micro-Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy analysis. PEC activity of ZNS@ZIF8 photoanodes was evaluated using the linear sweep voltammetry (LSV) technique, and the photocurrent density is significantly enhanced when ZNS are decorated with ZIF8 nanocrystals. Electrochemical impedance spectroscopy (EIS) revealed that ZNS@ZIF8 had low charge transfer resistance compared to pristine ZNS counterparts. This led to considerably improved PEC performance of ZNS@ZIF8. Mott–Schottky (M–S) analysis of ZNS and ZNS@ZIF8 revealed a shift of flat band potential for the ZNS and ZNS@ZIF8 photoanodes, respectively. The shift of flat band potential indicates a clear shift in the Fermi level towards the conduction band, leading to an efficient charge transfer process across the electrolyte. The carrier density of ZNS and ZNS@ZIF8 photoanodes increases from 3.67 × 1019 cm−3 to 4.11 × 1020 cm−3. The enhanced applied bias photon conversion efficiency (ABPE) of ZNS@ZIF8 photoanodes suggests that ZNS@ZIF8 can be a prospective candidate for PEC and optoelectronic applications.

Herein, we report the synthesis of highly stable, Pb-free bismuth iodide (BiI3 or BI), stoichiometric methylammonium bismuth iodide [(CH3NH3)3Bi2I9 or MA3Bi2I9 or s-MBI] and non-stoichiometric methylammonium bismuth iodide [(CH3NH3)2BiI5 or MA2BiI5 or Ns-MBI] perovskite thin films for photodetector applications. These films are synthesized at room temperature by a single step solution process spin coating method. The structural, optical, and morphological properties of these films were investigated using different characterization techniques such as XRD, Raman spectroscopy, FE-SEM, UV-Visible spectroscopy, etc. Formation of BI, s-MBI and Ns-MBI thin films is confirmed by XRD and Raman spectroscopy measurements. XRD analysis reveals that BI has a hexagonal crystal structure and a P63/mmc hexagonal space group for s-MBI and Ns-MBI. The optical properties of BI thin films show a high absorption coefficient (∼104 cm−1) and a band gap of ∼1.74 eV. Similarly, s-MBI films have a high absorption coefficient (∼103 cm−1) and an indirect band gap of ∼1.8 eV. Moving from s-MBI to Ns-MBI, the value of absorption coefficient is ∼103 cm−1 and the band gap corresponds to ∼2 eV. Finally, photodetectors based on the synthesized BI, s-MBI and Ns-MBI perovskites have been directly fabricated on FTO substrates. All photodetectors exhibited highly stable photo-switching behaviour along with excellent photoresponsivity and detectivity, with a fast response and recovery time. Our work demonstrates that Pb-free BI, s-MBI and Ns-MBI perovskites have great potential in the future for realizing stable photodetectors.

The copper oxide (CuO) nanostructures have been successfully synthesized from copper sulfate pentahydrate (CuSO4.5H2O) and NaOH as a stabilizing agent using simple hydrothermal chemical route. The prepared samples were characterized using x-ray diffraction, Raman spectroscopy, scanning electron microscopy, and UV-visible spectroscopy. The x-ray diffraction study of CuO nanostructures shows a monoclinic structure with average crystalline size 22 nm as calculated from the Debye-Scherrer’s equation. The hydrothermal technique used for the synthesis of CuO plays an important role in the formation of rod-like morphology. Optical study of CuO nanostructure facilitated estimation of bandgap to be 1.3 eV. The humidity sensing properties of CuO nanostructure are studied at a room temperature. The maximum sensitivity response was found to be 82.03 % which was stable and reproducible. The CuO nanostructures were successfully demonstrated as good candidate for humidity sensing application.

Carbon functionalized bismuth vanadate (BVO) photoanodes were synthesized using simple wet chemical process. To ascertain and determine various aspects of synthesized photoanodes, different types of characterization and measurements such as, X-ray Diffraction (XRD), Field emission scanning electron microscope (FE-SEM), UV–Visible (UV–Vis), Raman, Photoelectrochemical (PEC), Mott-Schottky (MS), and Electron Impedance Spectroscopy (EIS) have been carried out. Carbon functionalized BVO (C-BVO) photoanodes demonstrated superior photoconversion efficiency (η∼0.38%) and short circuit current (JSC∼0.50 mA/cm2 at 0.5 V vs. SCE) compared to pristine BVO. Bare BVO based PEC OR and AND logic gates have also been designed using pulsed white light beams. The PEC response reveals that for a white light beam with peak pump intensity of 100 mW/cm2, a photocurrent density of 83 μA/cm2 is generated at a bias of ∼0.5 V vs. SCE. Moreover, by tuning bias the photocurrent response can be inverted and further utilized to realize different logic operations simultaneously. The present study paves a new way for bismuth vanadate-based PEC computing devices.