Electrochemical degradation modes in bifacial silicon photovoltaic modules

Abstract

Motivated by the rapidly rising deployment of bifacial monocrystalline‐silicon photovoltaics (PV), we investigate the durability of various PV module packaging configurations with transparent coverings on both the front and rear sides of the module. We use a series of bifacial passivated emitter and rear cell (p‐PERC) mini‐modules with systematically varying outer cover materials (glass/glass, G/G, or glass/transparent backsheet, G/TB) and encapsulant chemistries (poly [ethylene‐co‐vinyl acetate], EVA; or polyolefin, POE). We study degradation modes over 1,000 hours of combined damp heat (DH) exposure and high system voltages that can cause potential‐induced degradation (PID) under positive, zero, or negative 1,000 V cell‐to‐frame bias. We analyze the degradation modes using a combination of current–voltage measurements, impedance spectroscopy, external quantum efficiency, and spatially resolved luminescence and thermal imaging. Our results highlight various types of degradation including shunting, enhanced recombination, and series resistance increases, and we use spatially resolved characterization to separately identify the localized effects. We show that multiple PID and moisture‐ingress degradation modes severely affect EVA‐containing modules, with previously reported PID processes under negative‐bias DH and a unique observation of rear‐side surface recombination in G/EVA/G modules under positive‐bias DH. We observe significantly less degradation in POE‐containing modules, where the G/POE/G configuration exhibits minimal degradation under all stress conditions that we employ.

Filed Study on the Severity of Photovoltaic Potential Induced Degradation

“…The difference in the PR ranges from 27.9% to 39.9% for the PID affected PV strings, whereas for the healthy PV string, the PR has dropped only by 0.3%. This result is surprisingly consistent with laboratory utilized PID testing results obtained by [9,12].…”

“…Prior work on PID has considered testing the PV modules under a controlled environment by applying the existing PID testing procedure: humidity 85%, PV surface temperature at 65℃ and bias the PV module with either + 1000 V or -1000 V, for at least 96 hours [9][10][11]. This test can, of course, lead to understanding how PID can affect the PV modules.…”

“…It creates either + 1000 V or -1000 V biasing for the affected PV string. The PID will then cause the PV modules to leak the current from the semiconducting material to the actual framing or glass [9]. Consequently, it will degrade the modules and cause a considerable drop in the output power production [10].…”

“…In addition, it is unidenti ed if repairing the grounding issue of the affected PID strings would result in an increase in the output power and improve the quality of the affected modules. As we understand from [9,[12][13], through electroluminescence (EL) imaging, PID can cause shunting, cracks, and breakdown areas at a solar cell level.…”

Chemical and mechanical interfacial degradation in bifacial glass/glass and glass/transparent backsheet photovoltaic modules

“…17 We observed signatures of PID-p at the center of the cell causing enhanced carrier recombination at the rear side, suggesting a temporary positive charge accumulation at the rear cell surface. 14 To date, the species responsible for PID-p has not been identified, but early studies suggest it may not be caused by sodium migration. ) and sodium silicate (Na 2 O) x (SiO 2 ) y.…”