As solar cell technology has progressed, it has evolved from BSF and PERC to highly efficient TOPCon, HJT, and BC. With each advancement, encapsulation materials must also improve to maintain optimal reliability and performance. While our previous articles discussed the Encapsulation Solutions For TOPCon and Heterojunction technology, we now turn our focus to the next advancement – Back-contact (BC) (see Encapsulation Solutions For HJT).
Back-contact (BC) solar cells stand out for their efficiency and aesthetics, as they eliminate frontside metallization, reducing shading losses. These cells can be integrated with various architectures, including PERC, TOPCon, and HJT, and continue to evolve into variants like TBC, HPBC, and HBC, pushing power conversion efficiencies even higher.
Packing BC: Bo Jin, overseas sales manager at HANGZHOU FIRST, presented the company’s encapsulation solutions for back-contact modules. The absence of front-side contacts in BC technology presents unique encapsulation challenges and opportunities. It allows for thinner encapsulants on the front, reducing material usage and costs, while the back side, which houses both positive and negative electrodes, requires enhanced insulation and thicker encapsulation layers for long-term reliability. Additionally, different BC architectures have specific anti-PID and anti-corrosion requirements that influence the choice of encapsulant materials, according to Jin.
HANGZHOU FIRST provides tailored encapsulation solutions optimized for each BC module type. For HPBC modules, POE or EPE encapsulants are recommended for the front side, with grammage not required to be more than 360 GSM, which ensures the required anti-PID protection. The back side can use EVA or white EVA, offering effective anti-corrosion properties. In TBC modules, which are typically glass-glass, POE or EPE encapsulants are used both on the front and back, with the latter requiring additional layers for anti-PID and anti-corrosion protection. HBC modules, which incorporate HJT cells, demand extra UV protection due to the higher UV sensitivity of these cells. POE, EPE or EVA encapsulants are suitable for the front, while the back side requires POE or EPE with high water resistance and enhanced durability (see Hangzhou First: Comprehensive Encapsulation Solutions For BC Modules).
At the product level, POE encapsulants stand out for their excellent anti-PID performance and high light transmittance. HANGZHOU FIRST has been developing POE encapsulants since 2012, introducing crosslinked POE, thermoplastic POE in 2016, and co-extruded EVA-POE films in 2019 to enhance performance. The company still categorizes EPE under POE, as the middle POE layer is what makes it special.
In his presentation, Jin showed how even minor impurity defects in encapsulants become highly visible due to the uniform and reflective surface of BC modules. HANGZHOU FIRST’s POE films are designed to eliminate such defects and are available in ultra-thin versions, with thicknesses ranging from 280 to 360 μm, according to Jin. Low shrinkage rates and strong adhesion to glass while preventing aesthetic imperfections are the other key characteristics of the film.
EPE encapsulants, with their 3-layer structure, incorporate a POE core layer specifically for PID resistance, customizable between 90 and 150 GSM. Extensive testing by HANGZHOU FIRST has identified 110 GSM as the optimal balance for PID protection, with ongoing research exploring further reductions. The company’s EP304 model includes a UV-transmitting version, enhancing module performance under different lighting conditions. Reliability tests confirm that 110 GSM POE layers in EPE encapsulants effectively safeguard TBC cells against PID degradation.
Beyond encapsulants, HANGZHOU FIRST also offers high-reflective black films that enhance both aesthetics and efficiency in BC modules. These 2-layer films feature a black cell-side surface and a white or black air-side surface, reflecting infrared light to improve energy capture. Designed for both glass-to-glass and glass-backsheet BC modules, the F806WH model achieves an average infrared reflectance of 75%. Reliability tests, including PCT, UV-DH, and high-temperature aging tests, confirm its color stability and resistance to material migration.
