In recent years, perovskite single junction solar cells (PSCs) and perovskite-based tandem solar cells (TSCs) have demonstrated significant advancements in power conversion efficiency (PCE) on the laboratory scale. However, the commercialization of this promising technology faces challenges related to upscaling without compromise in performance, high process expenses, and the use of hazardous materials. Specifically, solvent-based material deposition techniques, such as coating and printing, pose difficulties when applied to larger areas due to a substantial increase in solvent consumption and the potential use of harmful solvents, raising safety and environmental concerns.            
In this study, we investigate the viability of employing non-hazardous and environmentally friendly solvents, commonly referred to as "green solvents”, for the commercialization of PSCs and TSCs. We delineate the specific criteria that such solvents must meet to facilitate cost-effective, non-hazardous upscaling routes while preserving solar cell PCE. Our research proposes two fundamental approaches to tackle the aforementioned challenges, focusing on inkjet printing technology as an example: A one-step perovskite deposition with an adapted solvent system and processing parameters, and a highly optimized hybrid two-step perovskite deposition. For the hybrid two-step deposition process, inkjet printing is leveraged to introduce organic cation precursor materials into evaporated lead iodide thin films. This approach promises to overcome upscaling hurdles by addressing issues related to homogeneous thin film formation and conformity, particularly important for the fabrication of efficient TSCs.
Presented here are our latest results, achieved through meticulous optimization of the hybrid inkjet printing process. These efforts have led to the fabrication of PSCs that exhibit high PCE exceeding 18% and remarkable reproducibility, along with high conformity even on textured surfaces. Importantly, both fundamental approaches eliminate the need for the use of toxic solvents such as dimethylformamide.
We are confident that our research contributes valuable insights and practical strategies for a safer and more environmentally friendly scalable production of efficient perovskite photovoltaics, that brings the technology closer to the realization of large-scale commercial applications.