DEFECTS CHARACTERIZATION IN Cu(In,Ga)Se_2 THIN FILMS SOLAR CELLS BY BIASED PHOTOLUMINESCENCE

摘要

The dependence of photoluminescence of CIGS solar cells under applied voltage is investigated forsamples with two different buffer layers, CdS and ZnS. Photoluminescence under bias is a derivative method which issensitive to the electric field induced changes in the PL response. According to the theory based on simple transportequation, with increasing forward bias the PL intensity increases, reaches a maximum and keeps constant or decreasesagain. The PL maximum is reached in flat band condition, i.e. when the applied voltage is around the built-in voltage Vbi;.However, experimental results show dependence of Vbi with the buffer layer. Indeed, with ZnS buffer layer flat bandcondition is reached at 0.6–1 V while CdS samples seem to exhibit higher values. In this study, a model is developed tostudy the real influence of the buffer layer on photoluminescence. Simulation results show that the buffer/absorberinterface properties such as the interface states and band offsets are crucial for the determination of the built-in voltage.