Molecular Aggregates as Charge Transport Layers in Perovskite Solar Cells

The hole (H) and electron (E) transport layers (TLs) play a critical role in the performance of metal halide perovskite solar cells (HPSCs). Particularly, organic semi-conductive small molecules as HTLs/ETLs hold advantages of structural versatility, cost-effective synthesis as well as high batch-to-batch material reproducibility. In the past several years, researchers have paid a lot of attention to manipulating the optoelectronic properties and film-forming properties of the HTLs and ETLs by optimizing their molecular structures. This chapter provides an overview of the recent advances in the chemical engineering of the small molecule-based HTLs and ETLs, and at the same time summarizes the fundamental understanding of how the structures and aggregated states of the organic hole/electron transport materials influence the optoelectronic properties as well as the performance of the HPSCs. It begins with an introduction of the device structures and the working principle of the HPSCs, and then reviews the previous studies on the organic HTL and ETLs. Last, it highlights the key challenges for designing good-performing charge transport layers toward highly efficient and stable HPSCs, and provides an outlook for future research directions.