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

摘要

Quasi-2D hybrid halide perovskites have drawn considerable attention dueto their improved stability and facile tunability compared to 3D perovskites.The expansiveness of possibilities has thus far been limited by the difficultyin incorporating large ligands into thin-film devices. Here, a bulky bi-thiophene2T ligand is focused on to develop a solvent system around creatingstrongly vertically-aligned (2T)_2(MA)_6Pb_7I_(22) (n = 7) quasi-2D perovskite films.By starting with a poorly coordinating solvent (gamma-butyrolactone) andadding a small amount of dimethylsulfoxide and methanol, it is found thatvertical orientation and z-uniformity is greatly improved. These are carefullyexamined and verified using grazing-incidence wide-angle X-ray scatteringanalysis and advanced optical characterizations. These films are incorporatedinto 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 of0.96 V, and a fill factor of 73.8%. Furthermore, the quasi-2D absorbing layersshow excellent stability in moisture, remaining unchanged after hundreds ofhours. In addition, 2T is compared with the more common ligands butylammoniumand phenylethylammonium in this solvent system to developheuristics and deeper understanding of how to incorporate large ligands intostable photovoltaic devices.