Field Testing of PID-p Susceptible Bifacial PERC Modules: Impact of Light, Voltage and Module History ​

This work investigates the potential induced degradation-polarization (PID-p) of bifacial passivated emitter and rear contact (PERC) modules installed in the field at the Florida Solar Energy Center. 22 modules were stressed over 1 year under various voltage (-1500V, -3500, +1500V) and mounting configurations (close to ground, 2 meters from ground, close to roof). The positively stressed modules were anticipated to have experiences PID-p on their front side. However, no degradation was observed, as the light-induced recovery effect effectively counteracted the degradation. The negatively stressed modules experienced Pmax drops during 2 weeks before stabilizing at 5-6% loss. I-V and EL characteristics suggest a PID-p degradation on the rear side. Lower degradation rates are observed with lower voltage and when the mounting configuration allows more albedo light on the rear side to compensate for the degradation. PID-p is observed to stabilize at similar level for the voltage and mounting configuration tested with slightly lower Pmax in winter. EL imaging reveals that cells are not degrading at the same rate across a module. Some cells get darker and then brighter which corresponds to the silicon/passivation interface going through depletion and then inversion when enough positive charges are accumulated. After full light-recovery, the modules were tested again along with 22 brand-new ones to assess the impact of the module history. Results confirmed the trends observed in the first year with PID-p occurring at voltage as low as -600V and recovered modules degrading faster than brand-new ones.. Authors: Molto, Cecile [​University of Central Florida - Florida Solar Energy Center, Cocoa, FL, 32922, USA​] (ORCID:000000017083165X); Colvin, Dylan J [University of Central Florida - Florida Solar Energy Center, Cocoa, FL, 32922, USA]; Smith, Ryan M [Pordis LLC, Austin, TX, 78729, USA]; Hacke, Peter [National Renewable Energy Laboratory, Golden, CO, 80401, USA]; Li, Fang [Photovoltaic Reliability Laboratory – Arizona State University, Mesa, AZ, 85212, USA]. DOE Contract: EE0009345. Subjects: 14 SOLAR ENERGY