Sayantan Sil

Synthesis of rGO–Zn0.8Cd0.2S via in situ reduction of GO for the realization of a Schottky diode with low barrier height and highly enhanced photoresponsivity

A metal–semiconductor interface is an integral part of numerous electronic devices such as Schottky barrier diodes (SBDs). On the other hand, ever since graphene was isolated, there has been an impressive growth in the application of graphene to electronic devices. In this study, we present the synthesis of a reduced graphene oxide–zinc cadmium sulfide (rGO–Zn0.8Cd0.2S) composite via an in situ reduction of graphene oxide. Such a composite was applied to the fabrication of a Al/rGO–Zn0.8Cd0.2S SBD, and its performance was compared with the Al/Zn0.8Cd0.2S SBD. After current–voltage (I–V) measurements in the dark and under illumination, important diode parameters were obtained from the (I–V) characteristic curves. Due to the incorporation of graphene, the photoresponse of the Al/rGO–Zn0.8Cd0.2S SBD was enormously enhanced by 448% compared to its counterpart without rGO. Furthermore, the detectivity also increased significantly by 2 order of a magnitude. Moreover, a considerably lower barrier height of 0.16 eV was achieved with rGO–Zn0.8Cd0.2S compared to Zn0.8Cd0.2S (0.28 eV). The superior performance for the rGO–Zn0.8Cd0.2S-based SBD was analyzed and explained by the space charge limited current (SCLC) theory, which confirmed that the charge transfer kinetics improved vastly due to the incorporation of rGO. Notably, there was an exceptional 300% increase in the effective carrier mobility for rGO–Zn0.8Cd0.2S. The SCLC analysis of the charge transfer kinetics was also verified by photoluminescence and electrochemical impedance spectroscopy. These results demonstrated the beneficial impact of graphene on a Zn0.8Cd0.2S-based diode. Indeed, the rGO–Zn0.8Cd0.2S diode exhibited an impressive performance, with a considerably lower barrier height, highly enhanced photoresponsivity and detectivity. Overall, our extensive study reveals that rGO–Zn0.8Cd0.2S exhibits a great potential in the design of multifunctional optoelectronic devices.

Positron Annihilation Spectroscopic Investigation on the Origin of Temperature-Dependent Electrical Response in Methylammonium Lead Iodide Perovskite

Organic-inorganic hybrid perovskite has appeared as one of the leading materials for realizing solution-based high-performing optoelectronic devices. The charge transport properties in this class of material are quite intriguing and still need to be carefully investigated. The temperature-dependent electrical property of methylammonium lead iodide (CH3NH3PbI3) has been investigated by employing positron annihilation spectroscopy (PAS), which unambiguously reveals the gradual formation of open volume defects with the enhancement in temperature. The high-temperature ionic conductivity is due to the generation of both cationic (CH3NH3+) and anionic (I-) vacancies, possibly because of the elimination of methylammonium iodide (CH3NH3I) as identified from the coincidence Doppler broadening (CDB) of the positron annihilation spectroscopy. Further, the evolution of temperature-dependent defect density and corresponding electrical responses has been correlated with the structural phase transitions of CH3NH3PbI3. This is the first ever report of temperature-dependent PAS measurement on hybrid lead halide perovskites to understand the nature and the origin of its electrical characteristics arising due to the variation in temperature.

Development of large area nanostructured silicon-hydrogen alloy material with improved stability for solar cell application by argon dilution method

Here we have presented the results of large area (30 × 30 cm2) silicon-hydrogen alloy material and solar cell by argon dilution method. As an alternative to hydrogen dilution, argon dilution method has been applied to develop single junction solar cell with appreciable stability. Optimization of deposition conditions revealed that 95% argon dilution gives a nanostructured material with improved transport property and less light induced degradation. The minority carrier diffusion length (Ld) and mobility-lifetime (μτ) product of the material with 95% argon dilution degrades least after light soaking. Also the density of states (DOS) below conduction level reveals that this material is less defective. Solar cell with this argon diluted material has been fabricated with all the layers deposited by argon dilution method. Finally we have compared the argon diluted solar cell results with the optimized hydrogen diluted solar cell. Light soaking study proves that it is possible to develop stable solar cell on large area by argon dilution method and that the degradation of argon diluted solar cell is less than that of hydrogen diluted one.