Metal halide perovskites have raised huge excitement in the field of emerging photovoltaic technologies. The possibility of fabricating perovskite solar cells (PSCs) on lightweight, flexible substrates, with facile processing methods, provides very attractive commercial possibilities. Nevertheless, efficiency values for flexible devices reported in the literature typically fall short in comparison to rigid, glass-based architectures. Here, a solution-processable fullerene derivative, [6,6]-phenyl-C61 butyric acid n-hexyl ester (PCBC6), is reported as a highly efficient alternative to the commonly used n-type materials in perovskite solar cells. The cells with the PCBC6 layer deliver a power conversion efficiency of 18.4%, fabricated on a polymer foil, with an active area of 1 cm 2. Compared to the phenyl-C61-butyric acid methyl ester benchmark, significantly enhanced photovoltaic performance is obtained, which is primarily attributed to the improved layer morphology. It results in a better charge extraction and reduced nonradiative recombination at the perovskite/ electron transporting material interface. Solution-processed PCBC6 films are uniform, smooth and displayed conformal capping of perovskite layer. Additionally, a scalable processing of PCBC6 layers is demonstrated with an ink-jet printing technique, producing flexible PSCs with efficiencies exceeding 17%, which highlights the prospects of using this material in an industrial process.

Within a decade, perovskite solar cells (PSCs) leaped to the forefront of photovoltaic research, rapidly moving toward the industrial phase. Despite the impressive progress in technology development and new efficiency records, there still remains a large scope for further advancement. Utilization of scalable deposition methods and good control of the perovskite crystallization process, especially with industrially compatible fabrication protocols, require more understanding to ascertain reproducible, large-format manufacturing. Here, we report ink formulation development for ink-jet printing of perovskite thin films in ambient conditions. We used the precursor solution on a nonhazardous solvent system, fulfilling industrial requirements. By carefully adjusting the coordination environment of the Pb2+ through additive engineering, we were able to tune the nucleation process and achieve uniform, pinhole-free perovskite thin films. Furthermore, we combined multiple characterization techniques with computational methods to analyze Pb-complex structures and evaluate their influence on perovskite formation. Lastly, we applied ink-jet printed photoactive layers into large-area (1 cm2) photovoltaic devices and processed on flexible substrates (PET foil). Inverted (p–i–n architecture) PSCs, based on multication composition, Cs0.1[(HC­(NH2)2)0.83(CH3NH3)0.17]0.9Pb­(I0.83Br0.17)3, delivered 11.4% of power conversion efficiency.

perovskites remains one of the main challenges, adding risk to the long-term reliability of these devices. [3] Recently, perovskite compositions, which induce structures of reduced dimensionality, were reported as an interesting family of compounds, exhibiting promising environmental stability and effective photovoltaic performance parameters. [4,5] Within that category, Ruddlesden-Popper perovskite types were most often used in thin-film solar cells. Such layered structures, also referred to as quasi-2D perovskites, are described by the empirical formula of (LC) 2 (SC) n−1 Pb n I 3n+1 , where LC is a cation with a large ionic radius (usually an aromatic or aliphatic alkyl ammonium halide), SC is a small cation (typically, methylammonium -MA + , or formamidinium -FA + ), and n is the number of confined lead halide octahedral layers. [5] When the perovskite film is processed from a precursor solution, bulky cations organize in a specific way, separating the 3D-like phases, and forming a layered structure. The unique arrangement of the lattice brings certain properties, which can be further tuned with appropriate compositional engineering. [6][7][8] Many compounds of different chain lengths and chemical structures were found to fit the role of the bulky cation. [9,10] Commonly, these large organic cations provide hydrophobic character, enhancing the water resistance of the perovskite layers. [11] The large cation can also passivate various electronic defects in the perovskite structure, and limit ion migration, which in turn provides better photostability. [12] As a result, the quasi-2D perovskites provide an interesting avenue for reaching improved structural robustness and enhanced operational stability when compared to the more conventional 3D counterparts, making them particularly suitable for terrestrial applications. As the large organic cation is electrically insulating, the orientation of perovskite grains needs to be carefully adjusted. In order to enable efficient charge carrier transport through the photoactive layer, low dimensional perovskite sheets need to be oriented perpendicularly to the substrate. [13] Various strategies of inducing preferential vertical alignment of 2D perovskite crystallites have been explored, including coordinating additives, or specific processing conditions, inducing preferential dynamics of the initial crystallization stages. [14,15] Recent advancements in this topic resulted in PCEs exceeding 20%, highlighting the large application potential for these materials. [16] Metal halide perovskites of reduced dimensionality constitute an interesting subcategory of the perovskite semiconductor family, which attract a lot of attention, primarily due to their excellent moisture resistance and peculiar optoelectronic properties. Specifically, quasi-2D materials of the Ruddlesden-Popper (RP) type, are intensely investigated as photoactive layers in perovskite solar cells. Here, a scalable deposition of quasi-2D perovskite thin films, with a nominal composition of 4F-PEA 2 MA 4 Pb 5 I ...