An all-solution-processed interconnecting layer for highly reproducible and efficient tandem organic solar cells

Abstract

Tandem structure provides a practical way to realize high efficiency organic photovoltaic (OPV) cells due to the limited optical absorption in organic semiconductors and tandem cells can be used to extend the wavelength coverage of the solar spectrum for light harvesting. The interconnecting layer (ICL) between subcells in a tandem solar cell plays a critical role in the reproducibility and the performance of tandem devices, and the processability of the ICL in a tandem cell has been a challenge. In this work we report on the fabrication of highly reproducible high efficiency tandem cells by employing a commercially available material, PEDOT:PSS HTL Solar (HSolar), as the hole transporting material used for the ICL. Comparing with the conventional PEDOT:PSS Al 4083, HSolar offers a better wettability on the underlying non-fullerene photoactive layers, resulting in better charge extraction properties of the ICL. When FTAZ:IT-M and PTB7-Th:IEICO-4F are used as the front cell and the back cells to fabricate the tandem solar cells, a power conversion efficiency (PCE) of 14.7% is achieved. To validate the processability of these tandem cells, three other research groups have successfully fabricated tandem cells using the same recipe and the highest PCE obtained is 16.1%. With further development of donor polymers and device optimization, our device simulation results show that a PCE < 22% can be realized in tandem cells in the near future.