Pulsed Laser Deposition of Wide Band Gap Perovskites for Monolithic Perovskite/Silicon Tandem Devices

Perovskite-silicon tandem solar cells hold great promise due to high efficiencies (&gt; 33%) and low-cost materials [1,2]. However, the integration of the perovskite top cell, conformally and with uniform thickness onto the textured silicon wafers, still presents a challenge. Physical vapor deposition (PVD) methods facilitate conformal deposition and thickness control, but their full potential in fabricating the perovskite top cell has yet to be explored [3-7].<br/>In this work, we investigate the use of pulsed laser deposition (PLD) as a single-source physical vapor deposition technique to develop Cs_xFA_1-xPb(Br_yI_1-y)₃ films for p-i-n single-junction and monolithic tandem devices. Structural analysis via X-ray diffraction (XRD) confirms the formation of crystalline α-phase perovskite films with a preferential (100) orientation which showed to be crucial for a good device performance. Morphological characterization by scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveals the formation of dense and smooth films on both planar and textured silicon substrates at various deposition rates. Furthermore, by precisely controlling bromide ion incorporation in the PLD target, we demonstrate the tunability of the perovskite bandgap energy, ranging from 1.58 to 1.68 eV, as determined by photoluminescence measurements. This bandgap tunability enables optimal alignment with the underlying silicon absorber, and combined with thickness control, facilitates current matching conditions in monolithic device integration.<br/>Taking advantage of the conformal and rapid deposition with PLD and/or sputtering deposition, we also studied the formation of the inorganic scaffold in the hybrid sequential method, a widely used technique for fabricating perovskite top cells . A layer of PbI₂:CsBr (in 10:1 ratio) is deposited at a rate of ~ 55 nm/min and the formation of the perovskite layer is finalised with a spin coating of organic cation solution containing formamidinium iodide (FAI) and bromide (FABr) in ethanol. We compare the hybrid and single-step PLD method for the growth of Cs_xFA_1-xPb(Br_yI_1-y)₃absorbers, in terms of optoelectronic performance with respect to grain size, film orientation, surface passivation and final device performance.<br/>In conclusion, we underscore the potential of PLD in advancing the fabrication methodologies of perovskite-based monolithic tandem solar cells. With the added benefits of bandgap tuning, precise thickness control, and conformal coverage, this method shows promise for achieving efficient current matching conditions in monolithic perovskite/silicon tandem solar cells. Therefore, our aim is to contribute to ongoing efforts to optimize physical vapor deposition techniques for the scalable production of high-performance perovskite/silicon tandem solar cells.<br/><br/><b>References:</b><br/>[1] Best Research-Cell Efficiency Chart (https://www.nrel.gov/pv/cell-efficiency.html) [Access: 18th May 2024]<br/>[2] S. De Wolf, E. Aydin, Tandems have the power, <i>Science</i> <b>381</b>, 30-31 (2023)<br/>[3] T. Abzieher, et al., Energy Environ. Sci. <b>17</b>, 1645-1663 (2024)<br/>[4] M. Roß, et al., Adv. Energ. Mater. <b>35</b>, 11, 2101460 (2021)<br/>[5] F. Sahli, <i>et al</i>., <i>Nature Mater.</i> <b>17</b>, 820–826 (2018)<br/>[6] T. Soto Montero, W. Soltanpoor, M. Morales-Masis, APL Matter.<b> 8</b>, 110903 (2020)<br/>[7] T. Soto-Montero, et al., Adv. Funct. Mater, 2300588 (2023)