How nanotextured interfaces influence the electronics in perovskite solar cells

Abstract

Perovskite solar cells have reached power conversion efficiencies that rival those of established silicon photovoltaics. Nanotextures in perovskite solar cells scatter the incident light, thereby improving optical absorption. In addition, experiments show that nanotextures impact electronic performance, although the underlying mechanisms remain unclear. This study investigates the underlying theoretical reasons by combining multi-dimensional optical and charge-transport simulations for a single-junction perovskite solar cell. Our numerical results reveal that texturing redistributes the electric field, influencing carrier accumulation and recombination dynamics. We find that moderate texturing heights ($\leq 300$ nm) always increase the power conversion efficiency, regardless of surface recombination velocities. Our study also clarifies why experiments have reported that texturing both increased and reduced open-circuit voltages in perovskite solar cells: this behaviour originates from variations in surface recombination at the untextured electron transport layer. In contrast, surface recombination at the textured hole transport layer strongly affects the short-circuit current density, with lower recombination rates keeping it closer to the optical ideal. These findings provide new insights into the opto-electronic advantages of texturing and offer guidance for the design of next-generation textured perovskite-based solar cells, light emitting diodes, and photodetectors.

Figures (5)

• Figure 1: Overview of motivating experimental devices, simulated stack and simulation methods used in this study. (a) Scanning electron microscope (SEM) cross-section micrograph of the physical layer stacks investigated by Tockhorn et al.tockhorn2020improved and Sutter,Sutter22 showing planar (left) and textured (right) substrates. These devices showed improved efficiencies, which inspired the present work. The hole transport layer (HTL), electron transport layer (ETL), and the copper back contact layer are not visible. (b) The theoretical setup used for the optical and electronic simulations, depicting both planar (left) and textured (right) configurations. The material composition varies from the stacks in (a) and is taken from the literatureDiekmann2021LeCorre2022thiesbrummel2024ion due to available electronic data from these sources. (c) Schematic illustration of the three-step coupling procedure between optical and electronic simulations: A finite element (FE) mesh for the optical simulation (left), Cartesian grid points used for exporting the photogeneration rate (middle), and a finite volume (FV) mesh for the electronic simulation (right).
• Figure 2: (a) The optical photogeneration rate $G$ plotted as a function of position in the perovskite layer for cells with no texture (left panel), $300$ nm (mid panel), and $600$ nm (right panel) nanotexture height. (b) Total spectral reflectance ($R$), parasitic absorptance ($A_\text{par}$ in PTAA, Cu and ITO) and absorptance ($A_{\text{gen}}$) for no texture (left panel), $300$ nm texture (mid panel), and $600$ nm texture (right panel). The black dashed line indicates the absorptance for the non textured case of the first panel. The maximum achievable short-circuit current density $J_{\text{gen}}$ calculated from the photogeneration rate within the perovskite absorber is stated above each panel, respectively. (c) Dependence of the maximum achievable short-circuit current density $J_{\text{gen}}$ (top panel), the reflective losses $J_{R}$ (mid panel), and the parasitic losses $J_{\text{par}}$ (bottom panel) on texture height. The stars indicate the three textures shown in (a) and (b).
• Figure 3: Calculated performance metrics for the studied single-junction solar cell by solving the drift-diffusion charge transport model with a given optical photogeneration rate, computed from Maxwell's equations. (a) The device geometry (top) considered for the electronic simulations, consisting of the electron transport layer (C$_{60}$), the "83-17 triple cation" perovskite material layer, and the hole transport layer (PTAA). The thickness of the perovskite layer varies with the texture height $h_{\text{T}}$, while the texture width $w_{\text{T}}$ stays the same. Moreover, the considered measurement protocol (bottom) includes a preconditioning step, a backward and a forward scan. The following simulation results correspond to the grey shaded forward scan. (b) Simulated forward current-voltage ($J$-$V$) curves for cases $C_1$ to $C_4$, where the surface recombination velocities $v_{\text{HTL}}$ and $v_{\text{ETL}}$ are varied. Brighter colours indicate greater texture height, with arrows showing the direction of increasing texture height. Furthermore, we show for all test cases $C_1$ (grey), $C_2$ (orange), $C_3$ (green), and $C_4$ (blue), the impact of texture height on (c) the power conversion efficiency (PCE), (d) the short-circuit current density $J_{\text{SC}}$, (e) the open-circuit voltage $V_{\text{OC}}$, (f) the difference in $V_{\text{OC}}$ between planar (PL) and textured systems (NT), and (g) the fill factor (FF). The stars indicate the three texture heights shown in (b).
• Figure 4: Simulated voltage-dependent recombination current densities for planar and textured perovskite devices for the reference high-surface-recombination case $C_1$ (left) and the low-surface-recombination case $C_4$ (right) from drift-diffusion calculations, with the photogeneration rate obtained from Maxwell's equations. (a) Recombination current densities for the planar systems. We included radiative $J_{\text{rad}}$ and surface recombination at the PVK/HTL $J_{\text{SR, HTL}}$ and ETL/PVK interfaces $J_{\text{SR, ETL}}$ as well as Shockley-Read-Hall (SRH) $J_{\text{SRH}}$ recombination. These integrated recombination rates are compared to the generation current $J_{\text{gen}}$. Furthermore, we show for both recombination velocity test cases (b) $J_{\text{SR, HTL}}$, (c) $J_{\text{SR, ETL}}$, and (d) $J_{\text{SRH}}$ for varying texture height. The grey vertical line indicates the open-circuit voltage of the planar configuration. The arrows indicate the direction of increasing texture height. Colour coding indicates device morphology: blue corresponds to planar devices and yellow to strongly textured devices.
• Figure 5: (a) Electric field for three texture heights $h_{\text{T}} = 0, 300, 600$ nm for $V = 0$ V applied voltage. The colour and the stream plot indicate the strength $\Vert - \nabla \psi \Vert_2$ and the direction of the electric field, respectively. (b) The corresponding ratio between hole and electron density $n_\text{p}/n_\text{n}$ for $V = 1.2$ V applied voltage. (c) 2D device geometry with the vertical cross-section indicated (top), along which the carrier densities (bottom) are extracted. More precisely, we see one-dimensional profiles of the electron (blue) and hole densities (red) at an applied voltage $V = 1.2$ V for varying texture height. In the density plot, brighter colours indicate greater texture height, with arrows showing the direction of increasing texture height. All results correspond to the low-recombination case $C_4$.