Nanophotonic light management for perovskite–silicon tandem solar cells

Abstract

Perovskite-silicon tandem solar cells are currently one of the most investigated concepts to overcome 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 reflection and parasitic absorption losses occur, which add up to 7 mA/cm 2 .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, which are deposited onto sinusoidally structured substrates.

2D/3D Heterostructure for Semitransparent Perovskite Solar Cells with Engineered Bandgap Enables Efficiencies Exceeding 25% in Four‐Terminal Tandems with Silicon and CIGS

“…Hence, optical losses that reduce the photo‐generated charge carrier densities, both in the top and the bottom cell should be considered. For example, to reduce the reflection and transmission losses one can employ light management schemes such as nanophotonics or interlayers, [ 17,60,66–67,108 ] as well as further improve the PSC layer stack (e.g., optimization of layer thicknesses and refractive indices and reduction of parasitic absorption). [ 56,57,67 ] This is feasible, for example, by employing a p‐i‐n structure to eliminate thick spiro‐MeOTAD, [ 53,58,107 ] and more importantly by replacing the bottom and top ITO with less absorbing TCOs (which also possess a more suitable refractive index) such as indium zinc oxide (IZO), zirconium‐doped indium oxide (IZRO), or hydrogen‐doped indium oxide (IO:H).…”

“…Various strategies to reduce optical losses in tandem solar cells have already been suggested, [ 17 ] including optimization of the thicknesses and optical properties of the various layers [ 12,14,53,56–59 ] as well as implementation of additional layers, [ 59,60 ] micro‐ and nanotextures, textured foils, and anti‐reflection coatings. [ 9,53,58,59,61–67 ] Unfortunately, despite significant advances in developing phase‐stable and high‐efficiency wide‐bandgap PSCs with E g > 1.7 eV (APbI 1− y Br y , y > ≈0.3) in recent years, [ 68–72 ] these Br‐rich perovskite compositions suffer from severe recombination losses. [ 3,52,69,73,74 ] A common issue is photo‐induced phase segregation and subsequent funneling of charge carriers into iodide‐rich lower bandgap regions, [ 75 ] acting as radiative recombination centers.…”

Textured interfaces in monolithic perovskite/silicon tandem solar cells: advanced light management for improved efficiency and energy yield

“…However, until recently textured front-sides were not suitable for the deposition of perovskite layers with spin-coating that gives the highest efficiencies and process control to date. Despite first proofs of concept shown with smooth nano-textures, 10 full 11 or hybrid 5 vacuum perovskite deposition is needed to implement conformal coatings of the perovskite top cell. Alternatively, planar anti-reflection (AR) coatings, such as LiF or MgF 2 , or textured light management (LM) foils can yield further gains in photocurrents.…”

Antireflective nanotextures for monolithic perovskite-silicon tandem solar cells

“…Therefore the negative cosine structure, utilized in Ref. 4, is preferred for light management in perovskite Si tandem solar cells.…”

“…3 In a recent study we investigated the effect of nanotextures in the perovskite layer stack on the reflective properties of the tandem solar cells. 4 We used hexagonal sinusoidal nanotextures that have proven to strongly reduce reflection at silicon-oxide silicon interfaces. [5][6][7][8] Send correspondence to K.J.…”