EN IEC 62787:2021 pdf download – Concentrator photovoltaic (CPV) solar cells and cell on carrier (CoC) assemblies – Qualification.
The number of devices to be tested in each qualification test shall not be less than the sample sizes specified in Clause 8. In order to provide statistical meaning to the number of devices, IEC 61193-2 has been used since it assigns a defect probability as a function of number of samples.
The samples for each test of Table 1 and Table 2 shall be chosen randomly from the qualification lot. The qualification lot shall be a production lot of at least 1 000 bare cells/CoCs. The production lot shall be formed from at least two epitaxial runs and three metal/ARC depositions carried out in different weeks.
6 Marking
Due to the very small bare solar cell dimensions any marking on cell is usually not possible. Therefore, an ID mapping needs to be applied. Regarding CoC under test, they shall be clearly marked or identified for later tracking of data records. The required information for both bare cells and CoCs are:
— name, monogram, or symbol of manufacturer;
— type or model number;
— serial number:
— polarity of terminals or leads:
— the date, place of manufacture, and cell materials should be marked, or be traceable from the serial number.
7 Characterization methods for measuring the performance of bare cells and CoCs subjected to qualification tests
7.1 General
The optoelectronic performance characterization based on illumination I-V curves tries to identify optoelectronic performance degradation of test samples caused by the required qualification tests. Therefore, illumination I-V curve has to be performed before and after qualification tests. The goal of the illumination I-V curve is on the relative power degradation, not on the absolute power output. Scanning Acoustic Microscopy (SAM) is also required but only for CoCs.
In addition, electroluminescence mapping and dark I-V curve can provide diagnostic information about defects and changes within the device. Before and after qualification testing. dark I-V curve can be carried out for the voltage and current ranges of interest. Electroluminescence images are not explicitly suggested through this document, but they could be of great help when captured for each device at different current injection levels before and after some qualification tests.
7.2 Light I-V measurement
This is a compulsory characterization method. All test samples shall be measured at 25 C, under AM1.5D spectrum as specified in IEC 62670-1, and at an overall light intensity representative of the intended application. For the purposes of this characterization method, 1 sun equivalent of the AM1 .50 spectrum will have a total power density (Irradiance) of 0,1 W/cm2, so that a light intensity of 100 W/cm2 = 1 000 suns. The parameters and measurement methods for the light I-V measurement are defined in IEC 60904-1-1:2017.
7.3 Dark I-V measurement 7.3.1 General This is a compulsory characterization method for the Electrostatic Discharge (ESD) Damage Threshold test while is optional for the rest. The high operating current density of CPV devices, can sometimes mask detection of low level defects or the onset of degradation. Dark I-V measurements performed before and after a qualification test can provide a more sensitive measure of damage or degradation. The dark I-V measurement is a cost-effective method to monitor and diagnose power degradation of bare solar cells and CoCs following intermediate stress tests, or to monitor the electric performance stability of the control samples. 7.3.2 Procedure If the dark I-V is used for diagnostic purpose, it should be measured during initial measurements to establish a reference for later dark I-Vs. a) Choose a suitable power source, which could be a conventional DC power supply, as long as it will generate current up to 1,5 times the rated current point corresponding to the photocurrent at the specified maximum concentration. The current should be adjustable so that there are at least 30 separate points in the range of 10-4 to 1,5 times rated Isc at the specified maximum concentration. The interval of the points should be nearly equal-spaced with a lower pitch around Isci b) For CoCs, short the blocking diode by placing a jumper lead across the leads of the blocking diode, if there is one installed; c) Connect the power source’s positive lead to sample’s positive lead, and the power source’s negative lead to sample’s negative lead; d) Block completely the light impinging the cells; e) Temperature shall be controlled and repetitive in order to comparing measured I-V results; f) Apply current to the device and record current, voltage and temperature. Complete this procedure as quickly as possible to avoid significant heating of the devices during the test.