Controlling Crystallization of Quasi‐2D Perovskite Solar Cells: Incorporating Bulky Conjugated Ligands

Abstract

Quasi‐2D hybrid halide perovskites have drawn considerable attention due to their improved stability and facile tunability compared to 3D perovskites. The expansiveness of possibilities has thus far been limited by the difficulty in incorporating large ligands into thin‐film devices. Here, a bulky bi‐thiophene 2T ligand is focused on to develop a solvent system around creating strongly vertically‐aligned (2T)2(MA)6Pb7I22 (n = 7) quasi‐2D perovskite films. By starting with a poorly coordinating solvent (gamma‐butyrolactone) and adding a small amount of dimethylsulfoxide and methanol, it is found that vertical orientation and z‐uniformity is greatly improved. These are carefully examined and verified using grazing‐incidence wide‐angle X‐ray scattering analysis and advanced optical characterizations. These films are incorporated into champion solar cells that achieve a power conversion efficiency of 13.3%, with a short‐circuit current density of 18.9 mA cm‐2, an open‐circuit voltage of 0.96 V, and a fill factor of 73.8%. Furthermore, the quasi‐2D absorbing layers show excellent stability in moisture, remaining unchanged after hundreds of hours. In addition, 2T is compared with the more common ligands butylammonium and phenylethylammonium in this solvent system to develop heuristics and deeper understanding of how to incorporate large ligands into stable photovoltaic devices.

Accelerating materials discovery by high-throughput GIWAXS characterization of quasi-2D formamidinium metal halide perovskites

“…Various studies have explored the crystallization behavior and the resulting phase distributions in quasi-2D MHP systems, revealing that multiple parameters and factors, including solventsolute interactions, crystallization rates, ion diffusion behaviors and temperatures, can sensitively affect the resulting system. 20,[22][23][24][25][26][27] Among them, the most intuitive determinant controlling the final phase distributions of quasi-2D MHPs is the ratio of 2D:3D compositions. 21 Nevertheless, there is not a united, generalized principles on how to design the quasi-2D MHP system with an optimal 2D:3D ratio for high-performance MHP optoelectronics, even though many publications have already demonstrated excellent device performances.…”

“…21 In fact, the crystallization of quasi-2D MHPsa chemically complex materials systemis largely dependent on multiple physio-chemical factors. 20,[22][23][24][25][26][27] Particularly, the ratio of 2D:3D 4 compositions in the MHP precursors primarily influences the final phase constitution of the quasi-2D MHP films. 21 Notwithstanding, so far, there is no consensus or fundamental guidelines for designing an optimal 2D:3D composition ratio within a wide range of MHP compositional space exhibiting best optoelectronic performances.…”

Accelerating materials discovery by high-throughput GIWAXS characterization of quasi-2D formamidinium metal halide perovskites

“…4e), consistent with the observation in PL analysis. These findings clearly provide quantitative evidence for uniting the spread notions regarding the optimal quasi-2D composition, 21,23,24,44 which has no consensus to datefrom its first photovoltaic applications. 45 Recall that the phase distribution of the 3D-like MHP with excellent optoelectronic functionalities shows a similar trend when the thickness of the film is adjusted to the devicegrade-thick level.…”

“…Various studies have explored the crystallization behavior and the resulting phase distributions in quasi-2D MHP systems, revealing that multiple parameters and factors, including solventsolute interactions, crystallization rates, ion diffusion behaviors and temperatures, can sensitively affect the resulting system. 19,[21][22][23][24][25][26] Among them, the most intuitive determinant controlling the final phase distributions of quasi-2D MHPs is the ratio of 2D:3D compositions. 20 Nevertheless, there is not a united, generalized principles on how to design the quasi-2D MHP system with an optimal 2D:3D ratio for high-performance MHP optoelectronics, even though many publications have already demonstrated excellent device performances.…”

“…20 In fact, the crystallization of quasi-2D MHPsa chemically complex materials systemis largely dependent on multiple physico-chemical factors. 19,[21][22][23][24][25][26] Particularly, the ratio of 2D:3D compositions in the MHP precursors primarily influences the final phase constitution of the quasi-2D MHP films. 20 Notwithstanding, so far, there is no consensus or fundamental guidelines for designing an optimal 2D:3D composition ratio within a wide range of the MHP compositional space demonstrating best optoelectronic performances.…”