Temperature Coefficients in Compensated Silicon Solar Cells Investigated by Temperature Dependent Lifetime Measurements and Numerical Device Simulation

Silicon solar modules typically operate at a higher temperature than the 25 degrees C used for standard testing, and the temperature coefficient (TC) therefore might have a significant impact on the field performance. In this paper the temperature dependent behavior of compensated Si solar cells has been simulated using PC1Dmod6.2, using a combination of physical models which include the effect of both temperature and compensation doping. The simulations were based on experimental input measured on two high performance multicrystalline ingots of similar resistivity of similar to 1.3 Omega cm, as well as one ingot with a resistivity of 0.5 Omega cm. Two of the ingots are produced using Elkem Solar Silicon (ESS (R)), a compensated Si feedstock made using a metallurgical purification route, and the third is made from non-compensated reference material. Dopant concentrations as a function of height in the ingot were determined using a combination of experimental resistivity data, simulations and the Scheil equation. Temperature dependent lifetime images, measured on etched and passivated wafers after relevant solar cell processing steps were also acquired at different heights and used as input to the simulations. Taking all this into account, the simulated TC in the efficiency were found to be similar for the two 1.3 Omega cm ingots and slightly higher (less negative) in the 0.5 Omega cm ingot, mostly caused by differences in the TC of the short circuit current and fill factor. We find a reasonable agreement between the simulated and experimental TCs, with the main difference being a similar to 0.02 %/K more negative TC in the open circuit voltage in the simulated values. This corresponds to only a 6-7% relative deviation from the experimental values, showing the validity of the PC1Dmod model.