To achieve optimal optical performance and minimal reflection losses, a textured interface between perovskite and silicon sub-cells in perovskite-silicon tandem solar cells is needed. However, the perovskite solar cells fabrication method yielding the highest efficiencies, spin coating, is not compatible with the conventional random micro-pyramidal texture on silicon. This study focuses on creating periodic inverted micro-pyramidal textures in silicon through photolithography, reactive ion etching, and wet-chemical etching, enabling the deposition of fully textured perovskite solar cells with low reflectance on the textured silicon via spin-coating. This breakthrough lays the foundation for the fabrication of optically and electronically optimized perovskite-silicon tandem solar cells.
KEYWORDS: Tandem solar cells, Finite element methods, Solar cells, Photocurrent, Perovskite, Simulations, Reflection, Multijunction solar cells, Light absorption, Interfaces
In this contribution we study numerically, how sinusoidal nanotextures would affect the (optical) performance of all-perovskite tandem solar cells. The simulations are conducted with the finite element method (FEM) and consider solar cells in glass superstrate configuration. We correct for the multiple interactions between light that is reflected from the solar cell stack and the glass-air interface with an iterative scattering-matrix approach. To achieve current matching, we optimize the perovskite thickness of the top cell using the Newton method.
Results show that front texturing improves the photocurrent density with respect to the planar reference. Additional texturing between top and bottom cell hardly improves the performance. Full texturing leads to an increased photocurrent density, which can mostly be attributed to light trapping at the absorption edge of the bottom cell. Our study shows how texturing can help to further increase the efficiency of all-perovskite tandem solar cells.
KEYWORDS: Tandem solar cells, Perovskite, Optical simulations, Solar cells, Silicon, Oxides, Optics manufacturing, Silicon solar cells, Optimization (mathematics), Multijunction solar cells
Optical simulations of perovskite/silicon tandem solar cells show that nanotexturing both sides of the perovskite top cell yields the strongest antireflective effect. Cells with an intermediate texture in-between the perovskite and silicon sub cells perform comparably to configurations with a fully planar top cell. However, in experiment intermediate-textured solar cells perform slightly better than their planar counterparts. A numerical sensitivity analysis shows that this can be attributed to the thickness of a silicon oxide layer in-between the two sub cells: this thickness affects the optics for a fully planar top cell, but does not affect the performance for intermediate texturing.
Optical simulations of perovskite/silicon tandem solar cells show that nanotexturing both sides of the perovskite top cell yields the strongest antireflective effect. Cells with an intermediate texture in-between the perovskite and silicon sub cells perform comparably to configurations with a fully planar top cell. However, in experiment intermediate-textured solar cells perform slightly better than their planar counterparts. A numerical sensitivity analysis shows that this can be attributed to the thickness of a silicon oxide layer in-between the two sub cells: this thickness affects the optics for a fully planar top cell, but does not affect the performance for intermediate texturing.
We present optical simulations for a tandem solar cell consisting of a nanostructured thin-film perovskite top cell and a silicon heterojunction (SHJ) wafer bottom cell. The absorption and related current density are calculated using the rigorous simulations in the form of the finite element method for the nanostructured perovskite cell and a semi-empirical method for the SHJ cell. In order to reach the optimal value for the perovskite layer thickness we employ Newton’s method using derivatives obtained directly from the rigorous simulation. Using this we obtain an optimal layer thickness using typically one iteration step and eliminate the need for a parameter scan.
We compare the results for different sinusoidal nanotextures applied to different layers in the multilayer thin-film perovskite top cell. The nanotextures lead to a gain in absorption and power conversion efficiency in comparison to an optimized planar reference. We also present experimental results towards a realisation of the proposed structure. These results give valuable insight for the emerging field of high efficiency perovskite/SHJ tandem solar cells.
Recently, we studied the effect of hexagonal sinusoidal textures on the reflective properties of perovskite-silicon tandem solar cells using the finite element method (FEM). We saw that such nanotextures, applied to the perovskite top cell, can strongly increase the current density utilization from 91% for the optimized planar reference to 98% for the best nanotextured device (period 500 nm and peak-to-valley height 500 nm), where 100% refers to the Tiedje-Yablonovitch limit.* In this manuscript we elaborate on some numerical details of that work: we validate an assumption based on the Tiedje-Yablonovitch limit, we present a convergence study for simulations with the finite-element method, and we compare different configurations for sinusoidal nanotextures.
KEYWORDS: Perovskite, Tandem solar cells, Solar cells, Silicon, Absorption, Nanophotonics, Finite element methods, Computer architecture, Fourier transforms, Crystals
Currently, perovskite–silicon tandem solar cells are one of the most investigated concepts for overcoming the theoretical limit for the power conversion efficiency of silicon solar cells. For monolithic tandem solar cells, the available light must be distributed equally between the two subcells, which is known as current matching. For a planar device design, a global optimization of the layer thicknesses in the perovskite top cell allows current matching to be reached and reflective losses of the solar cell to be minimized at the same time. However, even after this optimization, the reflection and parasitic absorption losses add up to 7 mA / cm2. In this contribution, we use numerical simulations to study how well hexagonal sinusoidal nanotextures in the perovskite top-cell can reduce the reflective losses of the combined tandem device. We investigate three configurations. The current density utilization can be increased from 91% for the optimized planar reference to 98% for the best nanotextured device (period 500 nm and peak-to-valley height 500 nm), where 100% refers to the Tiedje–Yablonovitch limit. In a first attempt to experimentally realize such nanophotonically structured perovskite solar cells for monolithic tandems, we investigate the morphology of perovskite layers deposited onto sinusoidally structured substrates.
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