Smooth and highly-crystalline Ag-doped CIGS films sputtered from quaternary ceramic targets

Sputtering with copper indium gallium selenide (CIGS) ceramic targets could produce smooth CIGS thin films that are preferred for preparing two-terminal tandem devices. However, grain sizes prepared in this way are small and device efficiency was low. To increase the grain size, in this report, an Ag layer was pre-sputtered beneath CIGS. The Ag doping layer increased the grain size and improved the crystalline alignment. Consequently, the Ag-doped films exhibited improved charge mobility. From X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy characterizations, we obtained an optimized Ag thickness of 15 nm. Short-circuit current density (J(SC)), open-circuit voltage (V-OC), and fill factor (FF) were all improved after doping with 15-nm Ag. Increasing the annealing temperature from 550 degrees C to 575 degrees C, the grains was enlarged further, with the power conversion efficiency (PCE) increasing to 14.33% and V-OC to 545 mV. Upon the smooth CIGS film, a thin conformal perovskite layer was fabricated without polishing. This work demonstrates a simple way to fabricate smooth and highly-crystalline CIGS films that can be used for tandem solar cells.

Automated summary

Doping with silver can increase grain size and improve crystalline alignment of CIGS films, enhancing charge mobility. Optimizing the doping of 15-nm silver significantly improves short-circuit current density, open-circuit voltage, and fill factor. Increasing annealing temperature further enlarges grain size and improves power conversion efficiency.