Light Management Enhancement for Four-Terminal Perovskite-Silicon Tandem Solar Cells: The Impact of the Optical Properties and Thickness of the Spacer Layer between Sub-Cells

Abstract

Mechanical stacking of a thin film perovskite-based solar cell on top of crystalline Si (cSi) solar cell has recently attracted a lot of attention as it is considered a viable route to overcome the limitations of cSi single junction power conversion efficiency. Effective light management is however crucial to minimize reflection or parasitic absorption losses in either the top cell or in the light in-coupling of the transmitted light to the bottom sub-cell. The study here is focused on calculating an optimum performance of a four-terminal mechanically stacked tandem structure by varying the optical property and thickness of the spacer between top and bottom sub-cells. The impact of the nature of the spacer material, with its refractive index and absorption coefficient, as well as the thickness of that layer is used as variables in the optical simulation. The optical simulation is done by using the transfer matrix-method (TMM) on a stack of a semi-transparent perovskite solar cell (top cell) mounted on top of a cSi interdigitated back contact (IBC) solar cell (bottom cell). Two types of perovskite absorber material are considered, with very similar optical properties. The total internal and external short circuit current (Jsc) losses for the semitransparent perovskite top cell as a function of the different optical spacers (material and thickness) are calculated. While selecting the optical spacer materials, Jsc for both silicon (bottom cell) and perovskite (top cell) were considered with the aim to optimize the stack for maximum overall short circuit current. From these simulations, it was found that this optimum in our four-terminal tandem occurred at a thickness of the optical spacer of 160 nm for a material with refractive index n = 1.25. At this optimum, with a combination of selected semi-transparent perovskite top cell, the simulated maximum overall short circuit current (Jsc-combined, max) equals to 34.31 mA/cm2. As a result, the four-terminal perovskite/cSi multi-junction solar cell exhibits a power conversion efficiency (PCE) of 25.26%, as the sum of the perovskite top cell PCE = 16.50% and the bottom IBC cSi cell PCE = 8.75%. This accounts for an improvement of more than 2% absolute when compared to the stand-alone IBC cSi solar cell with 23.2% efficiency.

Two‐Terminal Perovskites Tandem Solar Cells: Recent Advances and Perspectives

“…Due to free‐carrier absorption, significantly increased parasitic absorption losses occur over the wavelength range of 850–1200 nm in the transparent electrodes, especially for layers beyond 100 nm thick. There are several well‐identified routes to minimize a parasitic loss, and one strategy is reducing the layer thickness of transparent electrodes . By adjusting the thickness of front ITO layers from 150 to 60 nm, both the parasitic absorption and reflection were efficiently decreased.…”

“…There are several well-identified routes to minimize a parasitic loss, and one strategy is reducing the layer thickness of transparent electrodes. [63] By adjusting the thickness of front ITO layers from 150 to 60 nm, [45] both the parasitic absorption and reflection were efficiently decreased. However, the optical simulation indicated that thicker ITO layers give rise to significant parasitic absorption, [64] whereas thinner layers result in a reduced fill factor (FF) due to high series resistance.…”

Recent Progress and Future Prospects for Light Management of All‐Perovskite Tandem Solar Cells

“…[ 16 ] Light management also deals with essential features, such as antireflection of the incident light, minimizing parasitic absorption in various layers of the cell, and light‐trapping within the absorber to maximize the short circuit current density ( J SC ). [ 17,18 ] There is a great opportunity to further enhance the efficiency of all‐PTSCs by virtue of light management strategies. First, the fabrication of wide‐bandgap and narrow‐bandgap PSCs with efficient light utilization is the key to improving the performance of all‐PTSCs.…”

All-Thin-Film Perovskite/C–Si Four-Terminal Tandems: Interlayer and Intermediate Contacts Optimization

“…This serves as an electrical decoupler between the top and bottom cells and should simultaneously allow for maximum transmittance between themselves. 7,8 Furthermore, tandem 4T cells also require intermediate transparent contacts for charge collection as well as allowing light to reach the bottom cell. Traditionally, with TCOs, the overall manufacturing cost is increased, and the device's performance is limited due to parasitic absorption.…”

“…As such, we aim to study and optimize the most identifiable part of a 4T device, which is the interlayer. This serves as an electrical decoupler between the top and bottom cells and should simultaneously allow for maximum transmittance between themselves. , …”