| Multicrystalline silicon solar cell with its lower cost and simple preparation process has occupied an increasingly important position in the solar cell power generation, but it also has the the presence of low reverse breakdown voltage and battery reliability problems because of many defect states, dislocations and grain boundaries which are brought by the multicrystaline silicon production process, itself the crystallization rate etc.Shading a part of solar panel, the other parts at the same array will produce a more than-13V reverse bias. If the reverse current is too high, the Joule heat will damage the battery even the whole solar panel. Therefore, the character of electronic breakdown is an important subject for polycrystalline silicon solar battery, which limits the maximal number of battery in a solar panel. For ideal network doping n+-p diode, the reverse bias is more than50V when the doping concentration is about p-1016cm-3. However, most polycrystalline silicon battery will be broken down even at a small bias lower than13V. To avoid this phenomenon and improve the stability and lifetime of a solar battery, it is crucial to investigate and understand the reverse breakdown mechanism of polycrystalline silicon solar battery further. Electroluminescence (EL) imaging was utilized to investigate spatial distribution of electric properties of solar cells based on multicrystals Si, and different patterns can be observed under variable voltage.In this paper, under variable reverse bias, different types and positions of light-emitting are observed, and measure J-V-T. By analyzing the reverse J-V-T function, it is found that the light-emitting between-8V and-12V is due to electrons tunneling from P-zone to N-zone and electronhole recombination; and from positive J-V-T curve, it is evidence that the tunneling is most interface defects induced, which can explain that the reason of different brightness of EL on variable bias. For further verify our conclusion, we investigated the different brightness position by SPV method. Through the change of the bandgap and surface potential difference, we find results are accordance with that of J-V-T curve.The focus of the last part in this paper is on monocrystalline silicon solar cells, and we also use EL method to understand the internal mechanism. |
