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While there has been rapid progress in the performance of perovskite solar cells, the details of film formation, effect of processing parameters and perovskite crystal structure are still under discussion. The details of the X-ray diffraction (XRD) pattern of the tetragonal phase of CH 3 NH 3 PbI 3 perovskite existing at room temperature are often overlooked, with unresolved (002) (at 2 θ = 13.99° for CuK α and q = 0.9927 Å −1 ) and (110) (at 2 θ = 14.14° and q = 1.003 Å −1 ) peaks considered to be one peak at 14°, leading to an inaccurate estimation of lattice parameters. In this study, we use an electrospray deposition technique to prepare perovskite films at room temperature, oriented in (002) and (110) directions, with (002) as the preferred orientation. The results of a detailed study on the emergence of the two orientations during perovskite formation are reported. The effect of process parameters, such as substrate temperature during deposition and annealing temperature, on the grain orientation was established using XRD and grazing incidence wide angle X-ray scattering (GIWAXS). The study suggests that an irreversible crystal reorientation from (002) to (110) occurs at high temperature during rapid annealing, whereas a reversible crystal thermal expansion is seen during slow annealing. Finally, the results of the grain reorientation are correlated with the film properties, and it is shown that the film with the dominant (110) orientation has improved morphology and optoelectronic properties. The detailed structural investigation and characterization presented in this study are important for the precise determination of crystal orientation and achievement of desirable photovoltaic properties of the absorber material by carefully observing the adjacent crystal plane peaks in the XRD pattern of the perovskite thin films. 

Excellent contact passivation and selectivity are prerequisites to realize the full potential of high‐material‐quality perovskite solar cells, first to maximize theinternalvoltage (or quasi‐Fermi‐level separation)iVwithin the absorber, then to translate this highinternalvoltage into a highexternalvoltageV. Experimental quantification of contact passivation and selectivity is, thus, key to improving device performance. Here, open‐circuit measurements ofiV_ocandV_oc, combined with surface photovoltage measurements, are used to systematically quantify the passivation—usingiV_ocas a metric—and the selectivity—defined asS_oc = V_oc/iV_oc—of a range of common carrier transport layers to wide‐bandgap (1.67 eV) perovskite absorbers. The resulting solar cells suffer from large voltage deficits, particularly when NiO_xis used as the hole transport layer, even though it provides better passivation than its polymer‐based counterparts (PTAA and PTAA/PFN). This indicates a poor selectivity of NiO_x(S_oc < 0.81 for NiO_x‐based devices), whereas devices using polymer‐based hole transport layers exhibit high selectivity (S_oc = 0.94–0.95). In agreement with recent reports, this low selectivity is attributed to the formation of an interlayer of non‐perovskite material with high resistance to holes at the perovskite/NiO_xinterface. These measurements also imply that the selectivity of the C60‐based electron transport layers is relatively good.