Degradation of PERC and Al-BSF Photovoltaic Cells with Differentiated Minimodule Packaging Under Damp Heat Exposure
Menghong Wang1, Alan J. Curran1, Eric J. Schneller2, Jing Sun3, Jianfang Dai4, Arushi Pradhan1, Shiyi Qin1, Erika L. Anderson1, Sean M. Morrison1, Muhammad Syaheen Sazally1, Laura S. Bruckman1, Kristopher O. Davis2, Bryan D. Huey5, Jean-Nicolas Jaubert3, Jennifer L. Braid1, Roger H. French1
1Materials Science & Engineering, SDLE Research Center, Case Western Reserve University, Cleveland, OH, United States
/2Materials Science & Engineering, University of Central Florida, Orlando, FL, United States
/3Canadian Solar Inc., Suzhou, Jiangsu, China
/4Cybrid Technologies Inc. , Suzhou, Jiangsu, China
/5Materials Science & Engineering, University of Connecticut, Storrs, CT, United States

In order to investigate the reliability of PERC and Al-BSF cells and how their performances are affected by module packaging materials, monocrystalline PERC and multicrystalline Al-BSF cells were fabricated as 4 cell minimodules with POE or EVA encapsulants, and with high, medium, or low water vapor transmission rate (WVTR) backsheets. Five minimodules of each of the 12 types (2 cell types and 6 module packaging combinations) were subjected to 500 hour steps of damp heat (85, 85 % RH) up to a total of 2500 hours of exposure. After each exposure step, minimodules and individual cells were characterized with I-V, EL, and Suns-Voc. Additionally, more advanced characterization methods including PL and EQE were performed at 0 and 2500 hours of exposure. The results show that the PERC cells were more stable than Al-BSF cells, in damp heat exposures, for all tested packaging types, with 4% and 5.8% power loss/1000 hours DH exposure respectively. However, the high WVTR backsheet performed poorly for both cell types, and the POE encapsulant correlated with more performance degradation of PERC cells, and the EVA encapsulant with more performance degradation  for the Al-BSF cells. Coupons of each module packaging combination were also characterized with FTIR and Yellowness Index (YI) through stepwise DH exposures, revealing crystalline changes in PVDF-based backsheet combinations in coupon exposures that do not exist for these materials separately.