Understanding Film Formation Morphology and Orientation in High Member 2D Ruddlesden–Popper Perovskites for High‐Efficiency Solar Cells

• Published in: Advanced energy materials 2018-01, Vol.8 (1), p.n/a
• Main Authors: Soe, Chan Myae Myae, Nie, Wanyi, Stoumpos, Constantinos C., Tsai, Hsinhan, Blancon, Jean‐Christophe, Liu, Fangze, Even, Jacky, Marks, Tobin J., Mohite, Aditya D., Kanatzidis, Mercouri G.
• Format: Article
• Language: English
• Subjects: 2D perovskites; Ammonia; Chemical Sciences; Crystal structure; Energy conversion efficiency; Engineering Sciences; Grain size; Grazing incidence; microstructure; Open circuit voltage; Perovskites; Photovoltaic cells; Physics; Silicon wafers; Solar cells; Stability; Substrates; Thin films; X-ray scattering
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201700979

2D Ruddlesden–Popper (RP) perovskites have recently emerged as promising candidates for hybrid perovskite photovoltaic cells, realizing power‐conversion efficiencies (PCEs) of over 10% with technologically relevant stability. To achieve solar cell performance comparable to the state‐of‐the‐art 3D perovskite cells, it is highly desirable to increase the conductivity and lower the optical bandgap for enhanced near‐IR region absorption by increasing the perovskite slab thickness. Here, the use of the 2D higher member (n = 5) RP perovskite (n‐butyl‐NH3)2(MeNH3)4Pb5I16 in depositing highly oriented thin films from dimethylformamide/dimethylsulfoxide mixtures using the hot‐casting method is reported. In addition, they exhibit superior environmental stability over thin films of their 3D counterpart. These films are assembled into high‐efficiency solar cells with an open‐circuit voltage of ≈1 V and PCE of up to 10%. This is achieved by fine‐tuning the solvent ratio, crystal growth orientation, and grain size in the thin films. The enhanced performance of the optimized devices is ascribed to the growth of micrometer‐sized grains as opposed to more typically obtained nanometer grain size and highly crystalline, densely packed microstructures with the majority of the inorganic slabs preferentially aligned out of plane to the substrate, as confirmed by X‐ray diffraction and grazing‐incidence wide‐angle X‐ray scattering mapping. Controllable tuning of the thin film properties of high‐n member layered Ruddlesden–Popper perovskites, BA2MA4Pb5I16, is achieved via a hot‐casting method using dimethylformamide (DMF)/dimethylsulfoxide (DMSO) processing solvent. Unlike the polycrystalline films grown from DMF, the optimized 3:1 DMF:DMSO films are essentially single‐crystalline with regularly stacked inorganic slabs, and deliver solar cell power conversion efficiencies up to 10%.