Scaling error of quantum efficiency measurements for heavily shunted cells in reliability research

Abstract

In photovoltaic (PV) cell and module reliability and durability research, it is of great importance to acquire an accurate quantum efficiency (QE) data of shunted cells which may be obtained after certain accelerated stress tests such as potential induced degradation (PID). The challenge in measuring accurate quantum efficiency of shunted cells stems from the interplay between the poor shunt resistance and the inherent impedance imposed by the traditional QE test equipment. Unless this test equipment related impedance is very, very low, the scaling error of the measured QE would be significant. A new very low impedance method which minimizes, but not totally eliminates, those erroneous drops in the QE system has been utilized to address the scaling error of the QE data of solar cells that have very low shunt resistances. This paper presents the challenges in measuring accurate QE of heavily shunted cells without measurement artifacts and the QE results obtained with and without the newly utilized low input impedance method.