In recent years, photovoltaic technology research and development and industrialization progress by leaps and bounds, solar cell mass production conversion efficiency continues to reach a new high, PERC as the current mainstream products in the industry has been a large number of mature applications, while efficiency improvement has also encountered bottlenecks, the industry technology focus from P type to N type. TOPCon has been widely concerned by the industry because of its low attenuation, high potential for efficiency improvement, and low cost of upgrading production lines, and has become the battery technology with the highest market share in the N-type field. In terms of the industrialization of TOPCon technology, in addition to the pioneer enterprise Zhonglai Optoelectronics, which began to be laid out as early as 2017, other major leading enterprises in the industry have also begun to lay out TOPCon production capacity and seize the market highland.
TOPCon battery efficiency advanced
The passivation contact structures that have been commercialized are mainly divided into two types:
1)基于非晶硅的a-Si:H(i)/a-Si:H (p+/n+);
2) SiOx/poly-Si (p+/n+) based on polysilicon;
The passivated contact battery using the former is called an HJT or HIT battery, and the passivated contact battery using the latter is called a TOPCon battery.
The birth of the TOPCon battery
In 2013, Feldmann et al. of Fraunhofer ISE in Germany, inspired by SIPOS, reported a battery with a mixed emitter structure of a-Si and μ-Si growing on the SiOx interface layer, called Tunnel Oxide Passivating Contacts batteries, referred to as TOPCon batteries.
Schematic diagram of the structure of TOPCon solar cells
The front surface of the TOPCon battery is the same as that of conventional N-PERT solar cells, which is the emitter of boron diffusion, using Al2O3/SiNx double-layer passivation film, the main difference is that a layer of extremely thin silicon oxide layer is oxidized on the back, and a phosphorus-doped microcrystalline amorphous mixed Si film is deposited on the surface of the oxide layer by PECVD, annealed at annealing temperature of 850 °C, showing the excellent passivation performance of the passivation contact structure, and the prepared battery efficiency is more than 23%.
Academic TOPCon battery efficiency advancement
In 2019
In 2019, Fraunhofer ISE increased the efficiency of N-type TOPCon batteries to 25.8%, creating a new efficiency record for N-type TOPCon batteries;
In 2020
In 2020, Fraunhofer ISE further optimized the compound loss and lateral transmission resistance loss of the emitter on a 25.8% efficiency battery, placing n+ TOPCon on the back of a P-type silicon substrate as the emitter, creating a TOPCon battery world efficiency with a conversion efficiency of 26%.
During this period, the German Hameling Solar Energy Research Institute (ISFH) also tried to combine the TOPCon structure with good passivation performance with IBC batteries in 2014, proposing for the first time a POLO-IBC (TOPCon structure IBC) battery with an open circuit voltage of 722 mV and a conversion efficiency of 23.9%, and increasing the efficiency of the POLO-IBC battery to 26.1% in 2018, creating a world efficiency record for IBC batteries with a TOPCon structure.
Schematic diagram of polo-IBC battery structure & World Efficiency Record POLO-IBC
Schematic diagram of the battery structure
The industry's TOPCon battery efficiency advancement
In June 2021, LONGi announced that it has achieved a conversion efficiency of 25.21% on the N-type TOPCon with an area of 242.97 cm, which is isH certified by the German ISFH.
In August 2021, Risen Energy reported that its 158.75-size (251.99 cm) N-type TOPCon battery has a conversion efficiency of 24.78%.
In September 2021, Jolywood reported that its 182-size (330.15 cm) N-type TOPCon battery has a conversion efficiency of 25.4% and is certified by the Chinese Academy of Metrology (NIM).
In the same month, Trina Solar reported that its 210-size (440.92 cm) TOPCon battery had a conversion efficiency of 24.54 percent.
In October 2021, Jinko reported that its 163.75-size N-type TOPCon cell had a conversion efficiency of 25.4%, which was calibrated by the JET testing laboratory in Japan.
According to theoretical calculations, the potential efficiency of TOPCon solar cells (28.7%) is closest to the theoretical limit efficiency of crystalline silicon solar cells (29.43%). At present, the maximum efficiency and potential efficiency of the current industrialized N-type double-sided TOPCon battery are still a certain distance away, and the efficiency of the TOPCon battery can be improved through the following ways:
1) Reduce the compound loss and carrier transmission loss in the emitter passivation area;
2) Reduce the non-ideal optical loss on the back side;
3) Reduce optical occlusion and reflection loss.
TOPCon's market share and future size forecast
After the industry fully subsidies, photovoltaic power generation needs to rely on its own competitiveness and traditional energy to carry out direct competition, truly realize the market-oriented self-sustainable development without relying on subsidies, and the industry competition pattern will also undergo major changes, a large number of inefficient and backward production capacity that cannot meet the requirements of "parity on the Internet" will be accelerated, and "higher quality, higher efficiency, lower cost" advanced photovoltaic products will occupy the market dominance.
ITRPV 2021 predicts that N-type battery technology is in line with the technical trend of market development, and the market share of N-type silicon wafers will gradually increase, and it is expected to reach 50% in 2031, becoming the mainstream silicon wafer type. According to the latest forecast results of PV InfoLink 2021, among many types of N-type batteries, the production capacity and shipments of TOPCon batteries will account for more than 50% this year, showing a gradually increasing trend, and will be in a dominant position in the future in N-type modules.
ITRPV predicts the market share of different silicon wafers
2020-2025 N-type module capacity and shipments