Study Of Infrared Thermography Temperature Measurement On Copper Indium Gallium Selenide Based Thin Films

Recently,copper indium gallium selenide(CIGS)based thin film solar cells stand out in the photovoltaic field due to their low energy consumption and low pollution during the preparation,good performance under dim light and long lifetime.The photoelectric conversion efficiency of the CIGS based solar cell mainly depends on the performance of the CIGS film/absorber,which can be improved through an accurate temperature control during the preparation.Consequencently,it is extremely important to monitor the temperature during the preparation of the CIGS based solar cells.To monitor the surface temperature of the film without interference,it is feasible to develop an accurate non-contact temperature measurement method.In this dissertation,an accurate infrared thermography temperature measurement(ITTM)was developed and applied in the temperature monitoring of the heated CIGS films,aiming to lay a foundation for the on-line temperature monitoring of CIGS films at growth state.The thermal properties,i.e.,specific heat,thermal conductivity and emissivity,of the CIGS film samples were measured and analyzed first.These samples have a uniform structure of "CIGS film+Mo+soda-lime glass".Because the total thickness of the CIGS film and Mo is far smaller than that of the soda-lime glass,the effect of the CIGS film and Mo on the specific heat and thermal conductivity of CIGS film sample can be negelected,meaning that the specific heat and thermal conductivity of the soda-lime glass can be approximated as the correspongding values of the CIGS film sample.The component of the CIGS film,which is related to the emissivity,can change during heating,and thus,a scanning electron microscope,an energy dispersive spectrometer and a X-ray diffractometer were used for sample characterization before and after emissivity measurement.Moreover,the transfer matrix method and effective media theory were adopted to analyze the emissivity variation of the film sample.The results show that the sample emissivity increases with temperature,and particularly,a rapid increase can be found when the temperature is above 400 ?,which is resulted from the oxidation of the Mo layer with the film broken at high temperature.Because the manufacturers of the infrared thermal imagers are generally reluctant to provide the spectral responsivity of their devices,the measured emissivities cannot be directly applied to the ITTM.In this case,according to the theory of ITTM,an apparent emissivity defined in a thermal imager's response band was calibrated without knowing its spectral responsivity,with which a method to acquire surface temperature through iteration solving was proposed.To verify the proposed method,ITTMs of an aluminium plate(AP)and a black paint sample(BPS)at approximate room temperature and ITTMs of a blackbody furnace(BF),a silicon carbide wafer(SCW)and an aluminium foil(AF)at mid-high temperatures were carried out.It was found that the measured temperature of the BPS is coincident with that from a thermocouple in the approxiamte room temperature measurement,whereas the temperature measurement of the AP does not work well because the reflected radiation of the AP is largely affected by the environmental fluctuation.For the temperature measurement at mid-high temperatures,the measured results of the three experimental objects show good agreements with those from thermocouples.The temperature deviation of the BF is within 3.7 ?.Regarding to the non-black-bodies,i.e.,the SCW and AF,the temperautre measurement accuracy can be affected by the apparent emissivity and background temperature.The maximal absolute deviation between the measured temperature of the SCW and that from a thermocouple is 9.3 ? at 563.0 ?,and the maximal absolute deviation for the AF is 5.7 ? at 265 ?.Uncertainty analysis shows that the dominating contributions are from the apparent emissivity and measurement accuracy of the infrared thermal imager.The method of ITTM was adopt to measure the temperature of the heated CIGS films.To model the growth environment of the CIGS films,a vacuum chamber integrated with an infrared window was developed,in which the wall temperature is controllable.Furthermore,ITTMs under two experimental conditions,i.e.,non-vacuum with the wall temperature controlled by a water bath,vacuum with the wall temperature controlled by liquid nitrogen,were carried out.It was found that the results of ITTMs under two experimental conditions are reliable.The results of former condition show that the CIGS films can react with air at high temperature,which makes the apparent emissivities increase rapidly.In the vacuum experimental condition,the accuracy of the temperature measurement can be improved because the sample does not react with air and the interference of the background radiation can be effectively reduced.The results of the two experimental conditions demonstrate that the ITTM can be used to measure the temperature of CIGS films accurately,which can lay a foundation for the on-line temperature monitoring of CIGS films at growth state.