Cu 2 ZnSnS 4 (CZTS)-based solar cells show a promising performance in the field of sunlight-based energy production system. To increase the performance of CZTS-based solar cell, buffer layer optimization is still an obstacle. In this work, numerical simulations were performed on structures based on CZTS absorber layer, ZnO window layer, and transparent conducting layer n-ITO with different buffer layers using SCAPS-1D software to find a suitable buffer layer. Cadmium sulfide (CdS), zinc sulfide (ZnS) and their alloy cadmium zinc sulfide (Cd 0.4 Zn 0.6 S) were used as potential buffer layers to investigate the effect of buffer thickness, absorber thickness and temperature on open-circuit voltage (V oc), short-circuit current (J sc), fill factor (FF) and efficiency (η) of the solar cell. The optimum efficiencies using these three buffer layers are around 11.20%. Among these three buffers, Cd 0.4 Zn 0.6 S is more preferable as CdS suffers from toxicity problem and ZnS shows drastic change in performance parameters. The simulation results can give important guideline for the fabrication of high-efficiency CZTS solar cell.

The performance of CZTS solar cell, a promising candidate in the field of energy production from sunlight, can be improved by optimizing the parameters of most widely used CdS buffer layer. In this work, numerical study have been done on the typical CZTS solar cell structures containing Mo thin film as back contact on glass substrate using SCAPS-1D solar cell simulation software. Then, the CZTS has been used as the absorber layer followed by CdS buffer later. Following, ZnO and transparent conducting oxide n-ITO layers have been considered as window layer and front contact, respectively. In the simulations, the CdS buffer layer has been doped with three different materials such as Silver (Ag), Copper (Cu) and Chlorine (Cl) for a wide acceptable range of carrier concentration. After obtaining the suitable carrier concentration, the thickness of the doped buffer layer has been varied keeping other layer parameters constant to see the variation of performance parameters open circuit voltage (V oc), short circuit current density (J sc), fill factor (FF) and efficiency (η) of the CZTS solar cell.

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The application of organic photodetectors (OPD) in photoplethysmography (PPG) sensors has rapidly improved the skin compatibility of the sensors providing high flexibility and low weight that is essential for continuous and real-time physical condition monitoring, Combination of OPD with organic or inorganic LEDs with proper circuitry and algorithm can detect noise free accurate heart rate signal and measure the oxygen saturation in blood, very crucial for everyone including the critical patients. The advancement of the PPG sensor with the application of OPD along with the challenges associated with it and its way of further improvement has been presented in this paper. The improvement of PPG sensors with OPD will speed up the accurate measurement of everyday health conditions and reduce the possibility of sudden failure of human health conditions.

The eco-friendly and highly stable lead-free MAGeI3 perovskite solar cell has proved itself as a potential candidate for conventional lead-based perovskite solar cells with high efficiency. In this paper, numerical simulation has been performed over MAGeI3 solar cell with three different Electron Transport Layer (ETL) and Hole Transport Layer (HTL) materials to obtain the best combination of ETL/perovskite/HTL layers using the solar cell simulation tool SCAPS-1D. The best performance has been found for the ITO/ZnO/MAGeI3/NiOx structure with an efficiency of 21.19% (Voc of 1.89 V, Jsc of 16.11 mA/cm 2 , and FF of 69.57%) due to the higher bandgap and better carrier mobility of these two ETL and HTL materials. The thickness optimization indicated that a thickness below 1000 nm is suitable for better performance which also leads to a good indication of making a lightweight solar cell. This study indicates that the use of low-cost and environment-friendly ZnO and NiOx with non-toxic MAGeI3 perovskite has the potential to obtain a highefficiency eco-friendly solar cell.