A Swiss research team has developed a new glowing process with one step for the passivating contact cells of tunneloxide-passivation sun cells. By demonstrating the approach, the scientists built a proof-of-concept Topcon device with an efficiency of 21%.
Researchers from École Polytechnique Fédérale de Lausanne (EPFL) and Center Suisse d’Entronique et de MicroTechnique (CSEM) in Switzerland developed a new single-step thermal glow process for tunneloxide-passioning contact (Topcon) solar cells.
The new process is intended to simplify the glowing process, which is currently implemented by the PV industry via a two-step technique and to reduce the payback time of Topcon PV energy. “We are convinced that slimmer processing is needed to reduce energy input during production and thus further reduce the payback time of the energy of solar cells,” said the corresponding author, Franz-Josef Haug, PV Magazine.
The proposed one-step process uses plasma-improved chemical vapor deposition (PECVD) to form drill-emitters at the front and at the rear polysilicon and Silicon (poly-si) Passivating the contact layer of the device. “To this end, we first studied the formation of drill channel by diffusion of drill-mooded silicon oxide (SIO𝑥) source layers,” said the researchers, adding that they were then able to adjust the surface concentration and depth of the drill protection profile by the PECVD parameters and the glow.
Secondly, they sought a suitable poly-si-based passivating contact for co-annealing. After evaluating contact on passivation, conductivity and resistance to surface cleaning via hydrofluoric acid (HF), standard clean 2 (SC2) and oxygen zone therapy (TI-o))) Treatment found the researchers that a standard Poly-Si (N) contact with thin Sio𝑥 showed resistance to HF, but had a bad tolerance for glowing at 900 C.
The issue was solved by introducing an extra plasma treatment of the nitrogen oxide (N2O), making it possible to reach a maximum of 720 mv at 900 ° C, compatible with a B-emitter in front.
In the final step, the group produced a proof-of-concept solar cell with different flow rates of Trimethylboron (TMB) and shooting temperatures with the help of the chosen conditions for the boring and poly-si passivating contact. “The variation in TMB streams was used to evaluate the influence of B-emitter profiles at cell level, while the shooting temperatures were varied to evaluate the effect of the pasta’s penetration on cell performance,” the team said.
The highest cell efficiency of 20.99% was found for the highest peak fire temperature at 840 ° C and an intermediate TMB current of 50 Standard cubic centimeters per minute (SCCM). The group said that the “promising” efficiency was achieved within just a few parties after using the new process.
The group emphasized that the work represents “some of the first proof that processing with one step can produce a diffuse emitter with a decline contact.”
It also gave a list of strategies for further improvements of the Boor -Memitter profile and ALO𝑥 Passivating to increase the efficiency “considerably”, some of which may require passivating contact from the rear “, as well as the use of laser-improved contact optimization (LECO) and printing techniques for fine line.
The study “Co-disladement of PECVD Boron-Emitters and Poly-Si Passivating contacts for slimmer Topcon Solar cell manufacturing“Appears in Solar energy materials and solar cells.
The researchers are currently investigating perovskiet/topcon tandem cells. “Most of the research into tandems is done with hetero junctions, but looking at the market share of technologies, integration in commercial modules is more rather with Topcon base cells,” Haug said.
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