Search

Industrial silicon solar cells are now moving further from passivated emitter and rear contact (PERC) toward Tunnel Oxide Passivated contact (TOPCon) technology. The efficiency of the PERC solar cell is improved by TOPCon technology, in which the rear side is fully passivated by an oxide/poly-Si tunneling junction. The performance of a TOPCon solar cell may further be improved by the incorporation of selective tunneling junctions underneath the front contacts. Some fabrications have been reported on a similar structure for an n-type Si substrate but they have not achieved the expected results. Also, a detailed study has not been done yet. Using 3-D sentaurus technology computer aided design (TCAD) simulation software, a detailed analysis has been done on the modified structure through the optimization of the tunnel oxides, the interfaces, the n++ poly-Si layer, the selective (SiO2/n++-poly-Si) tunneling junctions underneath the front contacts, etc., which has not been done earlier. It is seen that a thick n++ poly-Si layer causes parasitic absorption of light, whereas a very thin poly-Si layer cannot provide sufficient field for tunneling of carriers. A thicker tunnel oxide produces a high series resistance, whereas a very thin tunnel oxide cannot restrict the minority carriers to reach to the contacts. Therefore, an optimization is required and the optimization is done based on a fabricated bifacial p-TOPCon solar cell reported in the literature with an efficiency of 21.2% and bulk lifetime of 200 μs. After performing all the modifications in the fabricated reference cell and optimizing different parameters, the efficiency is improved by 3.5% in absolute. The efficiency is further improved to 25.4% with the bulk lifetime of 1 ms.

Industrial silicon solar cells are now mostly based on aluminum back surface field (Al-BSF) or passivated emitter rear cell (PERC) technologies on p-type crystalline silicon wafers. Recently tunnel oxide passivated contact (TOPCon) solar cell on p-type Si wafers has attracted attention due to its demonstrated higher efficiency than either Al-BSF or PERC type solar cell. Numerical analysis using 3-D Sentaurus Technology Computer Aided Design (3-D-TCAD) software leads to the enhancement of the efficiency of the p- and n-type TOPCon solar cells by optimizing the size, nature, and number density of pinholes in the oxide layer; thickness of the oxide layer with and without pinholes and B doping concentration in the hole selective p+ poly-Si layer at the rear. Effects of both types of pinholes, either completely through (physical contact) or partially through (localized thinner oxide), are studied on cell performance. Simulation results show that pinholes in tunnel oxide have an advantage in lowering of series resistance and improvement of fill factor. To achieve optimum performance, the size, nature, and number density of pinholes and thickness of the oxide layer should be optimized. Considering both types of pinholes, the efficiency achieved is 25.3% for p-TOPCon and 26% for n-TOPCon. Also, the outputs of simulated p-TOPCon are compared with simulated p-PERC solar cell. The analysis shows that TOPCon solar cell on p-type wafer has significant ability to be adopted for industrial production.

Passivated emitter and rear contact (PERC) on p‐type mono silicon has a roadmap for achieving >24% efficiency. The decrease of the full‐area rear metal contact to partial rear contact (<10%) accounts for the majority of the increase in efficiency of PERC solar cells over Al‐BSF solar cellswhich reached its maximum efficiency around 19.5%. P‐type tunnel oxide passivated contacts (TOPCon) solar cells have achieved further improvement in efficiency ≥25% by completely removing the partial rear metal contact and introducing a thin tunneling oxide layer at the rear. Thus passivating the partial rear and front metal contacts using SiOx/poly‐Si tunnelling layer stacks and an AlOx/SiNxstack on the entire back surface to passivate the remaining areas might lead to further advancements in PERC solar cells. Therefore, by integrating TOPCon and PERC architectures, as originally proposed by Fraunhofer lab, a modified design known as TOPerc solar cell has been studied in depth in this paper. Using 3D Sentaurus TCAD simulation software, a thorough numerical simulation of a p‐TOPerc solar cell has been performed. It is shown that efficiency of 25.2% and 26.0% is obtained for a p‐type wafer of bulk lifetime of 400 μs and 5.0 ms, respectively. The efficiency of p‐type passivated emitter and rear contact solar cells can be improved beyond 25% by passivating the partial rear and front metal contacts using SiOx/poly‐Si tunneling layer stacks, even at low bulk‐lifetime. Using 3D Sentaurus technology computer‐aided design simulation tool, optimizing the efficiency limiting parameters like poly‐Si thickness, doping, tunnel oxide thickness, pinholes, etc. achieved an efficiency of 26.0% for bulk‐lifetime 1 ms.

Photovoltaic (PV) industries are continuously trying to improve the module performance with the adoption of newer cell technologies. Recently, bifacial passivated emitter rear contact (PERC) solar cell technology has entered the market to further improve the module performance through the absorption of the extra photons reflected from the background. This work is mainly focused on optimizing the rear side grid pattern of the bifacial PERC solar cells for improvement of the total output power gain. We have developed an analytical model based on the front and rear grid pattern of commercially available bifacial PERC solar cells to calculate the optical shading and electrical losses for both sides of the solar cells. It is perceived that the rear shading loss due to rear grid design of industrial bifacial PERC solar cells is very high (∼30%) as compared to the front side (∼5%) of the cells. The model calculation shows that if with the improved laser scribing technology the finger width of the rear grid pattern be drastically reduced from ∼ 200 μm (measured value) to 25 μm the optical shading loss may be minimized to 11–14% from 30% without compromising the effective busbar resistance.

Disposed battery is a huge source of graphite in our environment. This graphite can be recycled by carrying out electrolysis at fixed voltage and the obtained product can be easily converted into graphene by the generation of graphene oxide (GO) as an intermediate using Hummer’s method. GO is converted into chemically reduced graphite oxide (CRGO) by sodium carbonate treatment and the material obtained is used as a filler in a drug (Ketorolac Tromethamine) loaded Hydroxypropyl methylcellulose (MC) matrix. The KT loaded CRGO\MC nanocomposite films is used to develop transdermal film for drug delivery where CRGO acts as a carrier. The recycled graphite (RGF), GO and CRGO materials has been characterized by Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Ultra-violet (UV) spectroscopy, Transmission Electron Microscopy (TEM), Thermo-Gravimetric Analysis (TGA) and Dynamic Light Scattering (DLS). KT loaded CRGO\MC nanocomposite films are characterized by TGA, XRD and moisture absorption properties analysis. The experimental result reveals the formation of successful exfoliated and stable KT loaded CRGO\MC transdermal film. XRD study reveals the crystalline nature of nanocomposite films. In vitrodrug release studies showed that CRGO\MC based films can be used for controlled transdermal drug delivery applications.

A simple and green chemistry approach for the preparation of reduced graphene oxide nanosheets was successfully demonstrated through the reduction of graphene oxide (GO) to obtain greenly-reduced graphene oxide (GRGO) using various green reagents. Without using toxic and harmful chemicals, this method is environmentally-friendly and suitable for the large-scale production of graphene. The prepared GO and GRGO were characterized by UV–Visible, X-ray diffraction, and Fourier transform infra-red spectroscopic analysis which showed a clear indication of the removal of oxygen-containing groups from the GO and the formation of GRGO. The morphology of the GRGO samples was characterized by transmission electron microscopy. Dynamic light scattering was used to measure the size of the GRGO particles along with zeta potential measurements. Electrical conductivity measurement was used to check the extent of reduction of GO to GRGO samples. The electrochemical properties of these carbonaceous materials were determined by cyclic voltammetry. The methods employed can lead to the preparation of GRGO can be effectively used in sensors and various electronic device fabrications.