Optical, structural and morphological study of CdS nanoparticles: Role of sulphur source

Cadmium sulfide (CdS) nanoparticles were synthesized by simple and low cost homemade hot injection method at low process temperature using different sulphur sources. The effects of sulphur concentration on the structural, morphological, and optoelectronic properties of synthesized CdS films were studied using a range of characterization techniques: X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM) and UV-Visible spectroscopy. The XRD studies revealed the formation of hexagonal type CdS nanoparticles. The varying morphology dependence on the sulphur source was ascertained from FESEM analysis. The longitudinal optical (LO) phonon vibrational modes of CdS were assigned in Raman spectra at 300 and 600 cm−1. The band gap of the CdS particles was estimated to be 2.30 eV from Tauc’s plots. Consistent with the experimental results, our first-principles DFT calculations predict the band gap of CdS nanoparticles to increase with decreasing S concentration: Cd52S52 (2.38 eV) Cd52S51 (2.52 eV) and Cd52S50 (2.65 eV), with both the valence and conduction band edges demonstrated to be dominated by S-p states

Photoelectrochemical investigation on the cadmium sulfide (CdS) thin films prepared using spin coating technique

Photoelectrochemical cell technology is one of the simplest technologies, which converts light energy directly into electricity. The synthesis of cadmium sulfide (CdS) nanocrystals (NCs) was performed by the facile hot injection method. The NCs were characterized by different techniques such as XRD, Raman, UV-Vis, FESEM, and XPS. The XRD pattern confirms the phase pure hexagonal CdS NCs. The band gap of NCs calculated from the UV-Visible spectrum is at 2.40 eV, indicating good absorption in the visible spectrum. XPS analysis confirmed the presence of individual elements in CdS NCs. The CdS thin-films having different thicknesses were prepared on FTO substrates using the spin coating technique. Photoelectrochemical (PEC) investigation of CdS NCs thin-films photoelectrodes was performed by varying its thickness. The increase in the thickness of thin-films increased photocurrent density

Revealing the electronic structure, heterojunction band offset and alignment of Cu2ZnGeSe4: a combined experimental and computational study towards photovoltaic applications

Cu2ZnGeSe4 (CZGSe) is a promising earth-abundant and non-toxic semiconductor material for large-scale thin-film solar cell applications. Herein, we have employed a joint computational and experimental approach to characterize and assess the structural, optoelectronic, and heterojunction band offset and alignment properties of CZGSe solar absorber. The CZGSe films were successfully prepared using DC-sputtering and e-beam evaporation systems and confirmed by XRD and Raman spectroscopy analyses. The CZGSe films exhibit a bandgap of 1.35 eV, as estimated from electrochemical cyclic voltammetry (CV) measurements and validated by first-principles density functional theory (DFT) calculations, which predicts a bandgap of 1.38 eV. A fabricated device based on the CZGSe as light absorber and CdS as a buffer layer yields power conversion efficiency (PCE) of 4.4% with VOC of 0.69 V, FF of 37.15, and JSC of 17.12 mA cm−2. Therefore, we suggest that interface and band offset engineering represent promising approaches to improve the performance of CZGSe devices by predicting a type-II staggered band alignment with a small conduction band offset of 0.18 eV at the CZGSe/CdS interface

Investigation of growth mechanism for highly oriented TiO2 nanorods: the role of reaction time and annealing temperature

Titanium dioxide (TiO2) is a versatile and inexpensive material for extended applicability in several scientific and technological fields including photo-catalysis for industrial waste treatment, energy harvesting, and hydrogen production. In this work, we report the synthesis of TiO2 thin film using hydrothermal method and investigations on the influence of reaction time and annealing temperature on growth mechanism of the TiO2 nanorods. The synthesized TiO2 films were studied by using UV–visible spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscope and energy-dispersive X-ray spectroscopy (EDS). The XRD and Raman measurements revealed the formation of defect free and pure tetragonal TiO2 rutile phase. The TiO2 thin films show absorption band edge at around 420 nm in the UV–visible spectrum and exhibit direct band gap value of 2.9 eV. The TiO2 nanorods are demonstrated to grow randomly on the FTO substrate with changing reaction times but grow uniformly in a flower-like pattern with increasing annealing temperature. Investigation of the field emission properties of TiO2 thin films (tested as field-emitter array) estimates the turn-on and threshold field at 4.06 and 7.06 V/µm at 10 and 100 µA/cm2, respectively

Investigations of the structural, optoelectronic and band alignment properties of Cu2ZnSnS4 prepared by hot-injection method towards low-cost photovoltaic applications

Cu2ZnSnS4 is a promising, versatile and inexpensive quaternary semiconductor with suitable optoelectronic properties for solar energy conversion. In this work, we report the synthesis of CZTS nanocrystals (NCs) using low-cost homemade hot-injection method. Oleylamine was used as both the binder and stabilizer for the CZTS NCs during the growth process. Detailed investigation of the influence of sulphur concentration and reaction temperature on the structural, stoichiometric, morphological, and optoelectronic attributes of CZTS NCs was carried out. The XRD, Raman, and TEM measurements confirm the formation of phase-pure tetragonal kesterite CZTS NCs. The synthesized CZTS NCs exhibit particle sizes in the range of 15–30 nm and display strong optical absorption in the visible region. The nearly optimal chemical composition of the CZTS NCs was confirmed by energy dispersive X-ray spectroscopy. UV–Visible spectroscopy and electrochemical measurements predicts the band gap of the CZTS NCs in the range of 1.3–1.6 eV, which is very close to the optimum values for the fabrication of single junction solar cells. The estimated conduction band offset (CBO) and valence band offset (VBO) of the CZTS-3M/CdS heterostructure are predicted as 0.11 and 0.98 eV, respectively, whereas for CZTS-225 °C/CdS heterostructure, CBO and VBO are 0.10 and 1.0 eV, respectively. The small conduction band offset measured at the CZTS/CdS interface are encouraging characteristics for the carrier transport and the deeper understating of band alignment and interface properties provides a hopeful approach for designing higher efficiency and more efficient carrier separation in CZTS solar cells

Ternary Cu2SnS3: synthesis, structure, photoelectrochemical activity, and heterojunction band offset and alignment

Ternary Cu2SnS3 (CTS) is an attractive nontoxic and earth-abundant absorber material with suitable optoelectronic properties for cost-effective photoelectrochemical applications. Herein, we report the synthesis of high-quality CTS nanoparticles (NPs) using a low-cost facile hot injection route, which is a very simple and nontoxic synthesis method. The structural, morphological, optoelectronic, and photoelectrochemical (PEC) properties and heterojunction band alignment of the as-synthesized CTS NPs have been systematically characterized using various state-of-the-art experimental techniques and atomistic first-principles density functional theory (DFT) calculations. The phase-pure CTS NPs confirmed by X-ray diffraction (XRD) and Raman spectroscopy analyses have an optical band gap of 1.1 eV and exhibit a random distribution of uniform spherical particles with size of approximately 15–25 nm as determined from high-resolution transmission electron microscopy (HR-TEM) images. The CTS photocathode exhibits excellent photoelectrochemical properties with PCE of 0.55% (fill factor (FF) = 0.26 and open circuit voltage (Voc) = 0.54 V) and photocurrent density of −3.95 mA/cm2 under AM 1.5 illumination (100 mW/cm2). Additionally, the PEC activities of CdS and ZnS NPs are investigated as possible photoanodes to create a heterojunction with CTS to enhance the PEC activity. CdS is demonstrated to exhibit a higher current density than ZnS, indicating that it is a better photoanode material to form a heterojunction with CTS. Consistently, we predict a staggered type-II band alignment at the CTS/CdS interface with a small conduction band offset (CBO) of 0.08 eV compared to a straddling type-I band alignment at the CTS/ZnS interface with a CBO of 0.29 eV. The observed small CBO at the type-II band aligned CTS/CdS interface points to efficient charge carrier separation and transport across the interface, which are necessary to achieve enhanced PEC activity. The facile CTS synthesis, PEC measurements, and heterojunction band alignment results provide a promising approach for fabricating next-generation Cu-based light-absorbing materials for efficient photoelectrochemical applications

Experimental and theoretical investigation on dtructural and Opto-electronic properties of Fe-doped lead-free Cs2AgBiCl6 double perovskite

Herein, we report the synthesis of Fe‐doped Cs2AgBiCl6 lead‐free double perovskite with blue emission using an antisolvent method. The crystal structure, morphology, optical properties, band structure, and stability of Fe‐doped double perovskites are investigated systematically. Formation of Fe‐doped Cs2AgBiCl6 double perovskite is confirmed by XRD and XPS analysis. XRD and TGA shows that the Cs2AgBiCl6 double perovskite has high structural and thermal stability, respectively. FE‐SEM analysis revealed the formation of dipyramidal shape Cs2AgBiCl6 crystals. Furthermore, EDS mapping shows the overlapping of Cs, Bi, Ag, Fe, and Cl elements and homogenous incorporation of Fe in Cs2AgBiCl6 double perovskite. The Fe‐doped Cs2AgBiCl6 double perovskite shows a strong absorption at 380 nm. It extends up to 700 nm, suggesting that sub‐bandgap states transition may originate from the surface defect of the doped perovskite material. The radiative kinetics of the crystals was studied using the TCSPC technique. Lattice parameters and band gap value Fe‐doped Cs2AgBiCl6 double perovskites predicted by the DFT calculations are confirmed by XRD and UV‐Visible spectroscopy analysis. Time‐dependent photo‐response characteristics for Fe‐doped Cs2AgBiCl6 double perovskite show fast response and recovery time of charge carriers. We believe that the successful incorporation of Fe in lead‐free, environmentally friendly Cs2AgBiCl6 double perovskite can open a new class of doped double perovskites with significant potential opto‐electronics applications, photocatalysts, and photovoltaics

Optical antenna effect on SiNWs/CuS photodiodes

One‐dimensional architectures between silicon nanowires (SiNWs) and CuS were fabricated by radio‐frequency (RF) magnetron sputtering and analyzed for solid‐state photodetector application. Inspired by the subwavelength optical concentration by the surface plasmons on metal nanostructures at the nanoscale, we investigated the effect of gold nanorods (AuNRs) on the optical absorption and photodetection properties of the heterojunction photodiode. AuNRs acting as an optical trapping antenna enhances the light absorption, consequently boosting the photocurrent from the device. A maximum photoresponsivity of 0.36 mA W‐1 was achieved under 665 nm excitation wavelength independent of the bias, a value ∼13 times higher than for the heterojunction photodiode without AuNRs. Such plasmonic sensitization can be useful for improving the sensitivity of visible as well as IR photodetectors

Emitter Passivation Of Silicon Solar Cell Via Organic Coating At Room Temperature

We present a simple method for passivation of silicon solar cells at room temperature. Oleylamine has been used as passivation agent on the n-type emitter of silicon solar cell surface. The desired effect is seen in the form of apparent enhancement in efficiency of the solar cell after coating. The efficiency increases by an amount of 14 % as compared to the one without any passivation applied and antireflection coating. The efficiency was found to decrease marginally and stabilized later. Device performance was monitored for 100 h and the efficiency was found higher as compare to bare solar cell without passivation coating