ANALYSIS OF BUILD-IN ELECTROSTATIC FIELD IN CDTE THIN FILM SOLAR CELLS BY QE MEASUREMENTS AT BIAS VOLTAGES

摘要

The purpose of the work is to understand the relationship between quantum efficiency (QE) at some typical bias voltage (BV) and build-in electrostatic field, and to develop a new method for analyzing the distribution of build-in electrostatic field in solar cells. In general, the external QE is an important characteristic about the performance of solar cells, however, in practice, the good QE curves not always belong to the good devices. It is considerable that QE is measured in short circuit condition under very weak incident light, which may not make any voltage in the both terminals of the cell. In contrast, when measuring the photo I-V curves a photogenerated voltage may apply the both terminals of the cell in a condition that a load resistance is larger than zero. The photogenerated voltage may drive a reverses current to photogenerated current, and also weaken the build-in electrostatic field or change its distribution, which would lead to alter QE curves. Therefore, it is necessary to measure QE of some typical solar cells at the different BVs and to understand the changes in QE and they effects on the performance of the cells.