Role of Terminal Group Position in Triphenylamine-Based Self-Assembled Hole-Selective Molecules in Perovskite Solar Cells
Ece Aktas, Rajesh Pudi, Nga Phung, Robert Wenisch, Luca Gregori, Daniele Meggiolaro, Marion A. Flatken, Filippo De Angelis, Iver Lauermann, Antonio Abate, Emilio Palomares
Abstract
The application of self-assembled molecules (SAMs) as a charge selective layer in perovskite solar cells has gained tremendous attention. As a result, highly efficient and stable devices have been released with stand-alone SAMs binding ITO substrates. However, further structural understanding of the effect of SAM in perovskite solar cells (PSCs) is required. Herein, three triphenylamine-based molecules with differently positioned methoxy substituents have been synthesized that can self-assemble onto the metal oxide layers that selectively extract holes. They have been effectively employed in p-i-n PSCs with a power conversion efficiency of up to 20%. We found that the perovskite deposited onto SAMs made by para- and ortho-substituted hole selective contacts provides large grain thin film formation increasing the power conversion efficiencies. Density functional theory predicts that para- and ortho-substituted position SAMs might form a well-ordered structure by improving the SAM's arrangement and in consequence enhancing its stability on the metal oxide surface. We believe this result will be a benchmark for the design of further SAMs.