TOPCon Solar Cells Achieve 22.8% Efficiency With Plasma-Aided Atomic Layer Deposition

The tunnel oxide deposition thickness was controlled at the atomic scale for higher efficiency

October 19, 2022


Researchers from China, Australia, and Singapore recently used a tube-type industrial plasma-assisted atomic layer deposition (PEALD) method and announced a maximum power conversion efficiency of 22.8% in a 613-Watt tunnel oxide passivated contact (TOPCon) module with 60 cells.

The study titled ‘Atomic scale-controlled tunnel oxide enabled by a novel industrial tube-based PEALD technology with demonstrated commercial TOPCon cell efficiencies >24%’, is published in the journal Progress in Photovoltaics.

The scientists claimed that plasma-assisted atomic layer deposition has the potential to enable improved quality, dense tunnel silicon oxide (SIOx) films at lower cost and with higher throughput.

All the films were deposited in a cell developed by the scientists using a G1 n-type wafer with a width of 170 μm and a surface area of 440.96 square centimeters. The films in the cell were initially subjected to heat at a temperature of 200 degrees Celsius for 25 seconds.

The teams used the plasma-enhanced chemical vapor deposition method wherein they designed an onsite doped poly-silicon (n+) layer, a uniform and ultrathin silicon oxide layer of approximately 1.3 nm at the crystalline silicon (Si) or SiOx or poly-Si (n+) interface.

In the entire process, the scientists claimed to have maintained the tunnel oxide thickness at 2.4 Å, showing the importance of controlling tunnel oxide thickness at the atomic scale for TOPCon solar cells.

The experiment yielded extremely low recombination current densities of 2.8 fA/cm2 and an implied open-circuit voltage (iVoc) as high as 759 mV.

The tube-type PEALD SiOx cells developed by the scientists resulted in solar cell efficiency and open-circuit voltage of up to 24.2% and 710 mV, respectively, in industrial TOPCon solar cells when they were tested under direct sunlight in standard illumination.

The researchers claimed that PEALD also enables mass production of TOPCon solar cells with enhanced efficiencies.

Researchers have pursued the atomic layer deposition method, a nanoscale fabrication technique, to design and study electronic devices in the last decade.

Emerging innovations in technologies like the internet of things (IoT) and quantum computing have also created scope for particularly plasma-assisted atomic layer deposition method, as it enables area-selective deposition, controlled growth of 2-dimensional materials, and atomic layer etching.

The scientists from Nantong University in China, the Institute of Materials Research and Engineering (IMRE) in Singapore, and Australia’s University of New South Wales collaborated with Chinese solar cell maker Tongwei, and China-based module manufacturer Risen Energy for the experiment.

In September, a proof of concept for an innovative production line for silicon solar cells with a double-than-usual throughput of 15,000 to 20,000 wafers per hour was developed by the Fraunhofer Institute for Solar Energy Systems ISE, a consortium of plant manufacturers, meteorology companies, and research institutions.

There is a significant push globally to accelerate research in various solar cell technologies with a focus on improving efficiencies. In April this year, the U.S. Department of Energy announced the launch of a Cadmium Telluride (CdTe) Accelerator Consortium, an initiative worth $20 million aimed at rapidly cutting the cost of the second most common photovoltaic technology in use worldwide after silicon.