In this work, a defective commercial module with a rounded IV characteristic is analyzed in detail to identify the sources of its malfunction. The analysis of the module includes thermography images taken under diverse conditions, the IV response of the module obtained without any shadow, and shadowing one cell at a time, as recommended by the IEC 61215 Standard. Additionally, a direct measurement of the IV characteristic and resistance of single cells in the panel has been conducted to verify the isolation between the p and n areas. In parallel, theoretical cell and module behaviors are presented. In this frame, simulations show how cell mismatch can be the explanation to the rounded IV output of the solar panel under study. From the thermal images of the module, several localized hot spots related to failing cells have been revealed. During the present study, thermal breakdown is seen before avalanche breakdown in one of the cells, evidencing a hot spot. Not many papers have dealt with this problem, whereas we believe it is important to analyze the relationship between thermal breakdown and hot spotting in order to prevent it in the future, since hot spots are the main defects related to degradation of modern modules.

The laser isolation of p-n junction is the origin of electrical damage in solar cells. Although several models explain this effect, it is usual to appeal to complex recombination mechanisms to get an accurate representation of their non-ideal I-V behavior. Other models give to an accurate and simple explanation of this damage introducing a connecting resistance of the defect to the rest of the solar cell structure, but its large resistance value is not well understood. This work uses electroluminescence techniques to validate the proposed model by means of finding the recombination paths from the cell volume to highly recombination defects and giving an explanation to this high value of the connection resistance from its two-dimensional behavior.

The recombination of the neutral regions of the solar cell is well modeled by means of an exponential term with ideality factor close to 1 in the low injection regime but non ideal performances evidenced in the I-V characteristic curves lead to diverse theories to explain the apparent high values of the ideality factor. This work analyzes a critical review of the existing explanations and clarifies their validity areas. Our experimental results indicate the evidence of high current areas that could be due to localized defects connected to the rest of the circuitry by a high connecting resistance.

High efficiency silicon solar cells are related to low recombination currents and high open-circuit voltages. The emitter is characterized by the impurity concentration profile. The usual parameters for this purpose are sheet resistance (Rs), surface impurity concentration (Ns) and depth junction. In order to obtain high quality emitter, we look for reduce Joe values, lowly doped emitters with low Ns and Rs values and deep depth junctions. A wet oxidation step is incorporated to minimize the dead layer and the peak surface concentration. Our work has developed a process resulting in ~ 0.8 × 1020 cm-3 and 60 Ω/□.