Impact of Vertical Inhomogeneity on the Charge Extraction in Perovskite Solar Cells: A Study by Depth-Dependent Photoluminescence

Abstract

In perovskite solar cells (PSCs), the vertical inhomogeneities which include uneven grains, voids, and grain boundaries are closely linked to the underlying charge transport layer which controls the nucleation and grain growth in the perovskite film. Herein, the vertical inhomogeneity of perovskite films in the device structure is analyzed by depth-dependent photoluminescence (PL) achieved with different excitation wavelengths. An analytical representation between vertical inhomogeneity and depth-dependent PL, parametrized with a factor, b, is introduced to understand the relation between inhomogeneity and charge recombination. Lower values of b correlate to lower vertical inhomogeneity and hence reduced recombination. The analytical representation is validated in two sets of devices that show remarkable differences in perovskite film morphology, device based on mesoporous TiO2 and planar SnO2. By exploring the morphological properties and the PL emission from different depths across the device structures, we show that the lower vertical inhomogeneity leads to more efficient charge carrier extraction in planar SnO2-based devices. Moreover, the SnO2-based devices exhibit lower Urbach energy, which concurs with the slow transient photovoltage decay, suggesting less defects and recombination losses. This work provides a broader understanding of the impact of vertical inhomogeneity on the charge extraction efficiency and presents a methodology to study quantitatively the inhomogeneity of perovskite films in device structures.

High‐Performance Tin–Lead Mixed‐Perovskite Solar Cells with Vertical Compositional Gradient

“…[34][35][36] As shown in Figure 2e, the front PL peak (979 nm) shows a clear red shift in comparison with the back PL peak (976 nm). Because a 360 nm excitation laser was used in the PL measurement, the penetrate depth in the perovskite film is only ≈50 nm, [37] so the peak shift can reflect different perovskite compositions on the top and bottom surfaces, respectively. The uneven metal element distribution along the vertical direction could be ascribed to the different crystallization dynamics between Sn-and Pb-based perovskites.…”

Disentangling X‐Ray and Sunlight Irradiation Effects Under a Controllable Atmosphere in Metal Halide Perovskites

“…The 7 keV X-rays penetrate through all perovskite layer while the UV-LED probes less than 50 nm. [37,43] Consequently, UV-LED emission originates from the surface and is more sensitive to environmental conditions, while X-ray probes the bulk. For instance, if the inner layers of the material had a more significant Br content, with I segregated to the surface, that would cause a redshift in the PL emission.…”

Reevaluation of Photoluminescence Intensity as an Indicator of Efficiency in Perovskite Solar Cells

“…Further, simple analyses to include the real device characteristics were performed comparing the PL quenching between OC and SC conditions. [21,[26][27][28] In particular, Du et al [21] found a linear relationship between the logarithm of the PL quenching and the power conversion efficiency (PCE) or the V oc . This linear relationship was found by analyzing three devices containing the same absorbing layer.…”