Effects of Growth Temperature on Electrical Conductivity in Low-Dimensional, Ruddlesden- Popper Perovskite Thin Films Deposited by RIR-MAPLE

Low-dimensional hybrid organic-inorganic perovskite (HOIPs) are being developed as wide bandgap, passivating layers on top of three-dimensional (3D) perovskite absorber layers to improve long-term device stability due to their greater resistance to moisture compared to the 3D HOIPs [1]. However, the same ligands that resist moisture, are also a barrier to charge transport, which can overshadow the significant advantages of using these materials as passivation layers in perovskite solar cells. Current work to overcome the charge transport challenge in low-dimensional perovskites focuses on: 1) achieving vertical orientation of quantum wells [2] and 2) increasing conductivity across the R-ligands and van der Waals gap via molecular modification [3]. Most studies focus on the first strategy and demonstrate vertical orientation, but do not show increased conductivity through the material, which is relevant for solar cell integration, thereby leaving a gap in the knowledge base. This work seeks to establish process-structure-property relationships to correlate a unique process (resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE)) to the HOIP structure (grain size and orientation), and subsequently, a relevant solar cell property (conductivity) in the specific case of
$\mathbf{n}=1,2\mathbf{D}$
perovskites. The deposition technique used here - RIR-MAPLE - is a modified pulsed laser deposition technique that has been previously demonstrated for deposition of 3D HOIPs [4],
$2\mathbf{D}(\mathbf{n}=1)$
Ruddlesden-Popper HOIPs [5],
$2\mathbf{D}(\mathbf{n}=1)$
Dion-Jacobson HOIPs [6]. In this study, (PEA)2PbI4 thin films are deposited by RIR-MAPLE at four growth temperatures (~10oC, 25oC, 50oC, and 75oC). Williamson-Hall analysis is used forthe average grain size of each film and scanning electron microscopy is used for changes in planar and cross-sectional morphology as a function of growth temperature. J-V measurements in the vertical and lateral directions of the film are used to investigate conductivity.