CIGS tandem on Silicon: an approach to stick around

A promising CIGS/Si 2-terminal tandem structure is explored in this contribution where the two subcells are bonded through the use of an optimized transparent conductive layer. This architecture avoids inherent issues related to direct growth of CIGS on top of a bifacial silicon heterojunction (SHJ) cell but requires optimization of the conductive and transparent bonding layers to enable gluing rough or textured surfaces. An in-house bonding process, based on PEDOT:PSS polymer, has been successfully optimized to glue a rough CIGS top cell with a textured SHJ cell. The first proof-of-concept bonded tandem device (~1 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) exhibits a remarkable Voc=1.28V. Electrical characterizations, including IV, EQE, and electroluminescence are performed to identify the key factors limiting efficiency. These experimental insights are further analyzed using an optical model, which predicts the current-limiting cell, evaluates current matching, and provides a detailed analysis of optical losses, providing clear directions for future optimizations.