Implementation of Tunneling Junction Passivated Contact Concept in Flexible CIGS Solar Cells

Abstract

In today's state-of-the-art high-efficiency silicon solar cells need to be inserted a thin insulating layer in order to reduce the recombination losses between the carrier transport layer and Si surface, which can form a tunneling junction (TJ), thus increasing the performance of the TJ solar cells comparable with the pn junction structure. However, the copper indium gallium selenium (CIGS) solar cells inevitably lead to the losses of the carrier transport due to the interface which is widely assumed as the pn-heterojunction. Herein, the TJ solar cells, aiming to enhance the performance of the solar cells, are fabricated by inserting the TiO2 between CIGS/CdS interface deposited by atomic layer deposition (ALD). By inserting the TiO2 insulating layer, the CIGS/TiO2/CdS structure can be effectively reduced the interface recombination, which leads to a reduced band bending in the p-CIGS surface and compromises its field-effect passivation. As a result, the CIGS solar cell with the tunneling junction achieves the 15.57% based on the stainless steel (SS) substrate, by introducing a barrier layer and doping NaF. These results provide an important preliminary foundation for the development of the CIGS solar cells with the tunneling junction structure.