4-terminal and 2-terminal tandem modules in bifacial operation: Model analysis and comparison

This paper models and compares the energy yield to be expected from bifacial 2-terminal (2T) and 4-terminal (4T) hybrid perovskite/crystalline silicon tandem modules. Following the work by Asadpour et al. the comparison includes 2T tandem cells employing a thick perovskite absorber layer with standard band gap, which in monofacial operation have significant mismatch of short circuit currents of top and bottom cell, and therefore low efficiency. The perovskite stack properties are taken from the current Solliance high-performance semi-transparent perovskite cells, and the c-Si model represents current high-efficiency industrial nPERT cells. As shown by Asadpour et al., the combination of thick absorber and standard band gap with bifacial operation is a promising approach for 2T bfiacial tandem modules, resulting in higher performance than the c-Si bottom cells. We find that such a 2T bifacial tandem module should be able to outperform even an optimized 2T module with wide band gap perovskite. Additionally, employing a planar c-Si front side in combination with textured module glass can potentially perform nearly as well as employing a textured c-Si front side. These results support the feasibility of important simplifications for production of 2T tandem modules, as long as these will be operated bifacially. The dependence of energy yield of 2T bifacial tandems on albedo is qualitatively different from that of 4T and single junction c-Si bifacial modules. This reduces the competitiveness of 2T bifacial tandems, compared to 4T and SJ c-Si, with increase of the albedo of the environment