Recently, Suzhou Maxwell Technologies Co., Ltd. (Maxwell) worked with Cybrid Technologies Inc. (Cybrid) to develop a new high-efficiency HJT module using a light conversion film, which increases the power of the module by more than 5W.
HJT technology has become one of the most promising next-generation photovoltaic technologies due to its ultra-high solar cell efficiency, excellent power generation performance, simple production process, and low product carbon footprint. The ultra-high photoelectric conversion efficiency of HJT-based products largely stems from the ability of intrinsic amorphous silicon to provide excellent surface passivation on crystalline silicon. However, there is a defect: The current of HJT cells is lower than that of ordinary ones because the TCO film and the amorphous silicon film absorb ultraviolet rays.
To make up for this shortcoming, Maxwell has partnered with a lot of reputable adhesive film manufacturers to promote the development of photoelectric conversion films. Through such a film, ultraviolet light with a low photon response for HJT solar cells can be converted into blue light or red light with a higher photon response, thereby increasing the power of a 60-cell M6 HJT solar module by more than 5W.
Amazing light conversion materials
Light conversion materials are not new things to the solar industry. They are quantum dot materials made of specific elements, which can absorb and emit photons at different wavelengths as their outer electrons travel from one orbit to another. For HJT technology, the important value of light conversion materials is that they absorb ultraviolet light and convert it into visible light with nearly 100% responsivity, so they can boost the current of solar cells and enhance the power of modules while the converted photons have no negative impact on the interface passivation of HJT products.
Significant gain for HJT module power
With light conversion materials, the newly developed HJT module converts ultraviolet light into blue light at a wavelength of around 450nm. Comparing the HJT module with the benchmark module, the R&D team has found that the ultraviolet spectral response of HJT solar cells of the former is substantially enhanced to more than 60%. According to the spectral integral method, if the spectral response could be fully transformed into module power, the power would increase by 0.8% to 1%. In addition, traditional PERC modules cannot get greater improvement from light conversion materials as their ultraviolet spectral response is high enough.
In the actual manufacturing process of HJT modules, the most commonly used adhesive films in the photovoltaic industry are highly permeable films and UV cut-off films. A module with highly permeable films has greater initial power than that with UV cut-off films, but the latter shows less power degradation. The power of both will be at the same level after exposure to ultraviolet light. A module that features light conversion films combines the advantages of both. It has the same initial power as the module with highly permeable films and equals the module with UV cut-off films in power degradation. The more-than-one-month power generation tracking observation of Maxwell's experimental power station shows that the visual module made with light conversion films performed very well in converting ultraviolet light into blue light (see Fig. 2). A comparison of power generation data reveals that the power generation per watt of the light conversion film-based module was equivalent to that of the highly permeable film module, without power degradation.
Fig. 1 Test data of external quantum efficiency (EQE) of PERC and HJT with different adhesive films
Fig. 2 The light conversion film-based HJT module (indicated by the arrow) looks much bluer than others as it converts ultraviolet light into blue light.
The experimental data indicates that light conversion materials have a great application prospect in HJT products. Maxwell calls on industry players to jointly advance HJT technology for the following goals:
1. Optimize light conversion materials and the dispersion process for the materials in the packaging films so that a light conversion film-based module has power 1% greater than that of a highly permeable film and gets a relative gain of 10W in the module end.
2. Optimize the weather resistance of light conversion films, ensure that light conversion film-based modules pass the threefold IEC test, and keep the effectiveness of light conversion materials in the acceleration test.