Predictive Models and Novel Accelerated Tests for the Reliability of Cell Metallization in Photovoltaic Modules (Final Report)

Abstract

Design test structures and induce metallization corrosion on the test structures. (M 1-M 10) NREL and SunPowerTask Summary: NREL and SunPower together will design coupons and test structures to monitor metallization corrosion which will be induced in damp heat chambers and under an applied bias (either with a foil on the glass or a grounded frame nearby). Extensive analysis of the coupons and test structures will be initiated. Task Details:The risk in this task is the identification of suitable test structures that mimic coupon level corrosion. Risk mitigation is to build test structures with the same type of metallization as in the actual cells. Subtask 1.1: Design coupons and suitable test structures to mimic corrosion in the cell.(M I-MS) NREL and SunPowerA paint corrosion-testing cell was used to conduct electrochemical testing of front-contact cells (FCCs) and back-contact cells (BCCs) in deionized water [6], Figure 1. The FCC cells were typical commercial Al back surface field cells, and the BCC cells were commercial SunPower cells. The total test area was 13.1 cm 2 , with a solution volume of 40 mL. Vacuum grease was applied to the O-ring to prevent water leakage between the corrosion cell and the samples. A graphite rod was used as a counter electrode, while a saturated calomel electrode (SCE) was employed as the reference electrode. The cathodic polarization measurement was initiated from 10 mV vs. open circuit potential after 10 min delay in the deionized water (to obtain steadystate), and the scanning rate was 0.5 mV/s. Si cells were rinsed with ethanol and deionized water to clean the surface and were then dried using compressed air.This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Table 5. Transient current characteristics of test samples. Data from the first Voltage-On cycle was ignored in these calculations. For most samples, only one measurement was made, but for some duplicate measurements were made and sometimes with different cycle times as indicated.