Perovskite/silicon tandem solar cells have demonstrated rapid progression of power conversion efficiency in the past decade. However, little effort has focused on integrating scalable deposition technique to industry-relevant silicon bottom cells. In particular, the relationship between coating defects and tandem cell performance loss is rarely reported. First, we discuss the effect of the silicon substrate non-ideality (trenches and texturing) on the perovskite film properties. Then, we perform a rigorous defect categorization using PL images and SEM to classify coating defects into 9 categories. Finally, we present a Failure Mode and Effects Analysis (FMEA) that reveals the three main defects causing performance loss in 2-terminal perovskite-silicon solar cells.

Shunting is a known problem in perovskite (and perovskite/silicon tandem) solar cells, with shunts able to form both during manufacturing and during device operation. In this work, we describe the evolution of shunting in perovskite/silicon tandem solar cells undergoing accelerated stress testing as measured through JV, electroluminescence, and dark lock-in thermography. We observe changes in shunts that existed due to manufacturing defects, as well as the formation of new shunts. We find that a perovskite/silicon tandem solar cell undergoing 24 hours of light exposure changes in power conversion efficiency by -1.2% absolute, and we observe a shunt burning out during the test. We also find that during reverse bias testing at -20 V for 20 minutes a new shunt forms at a manufacturing defect, leading to a -5.9% absolute change in power conversion efficiency. With these observations, we obtain a greater understanding of the relative importance of pre-existing shunts and manufacturing defects during different stress tests.

Perovskite-silicon tandem cells have shown much higher efficiencies than single-junction cells, which promises further reduction of energy cost from photovoltaics. Due to the protection by perovskites, silicon subcells in perovskite-silicon tandem cells may last much longer than those in single-junction devices. Herein, we report recycling silicon bottom cells from end-of-life perovskite-silicon tandem solar cells, which further reduces their cost and enhances the sustainability. We demonstrate that silicon bottom cells can be recycled from end-of-life tandem cells by thermal delamination and chemical cleaning processes. The optoelectronic properties of silicon bottom cells were shown to be largely unchanged in the end-of-life tandem cells. The efficiencies of tandem cells refurbished from recycled silicon bottom cells are comparable to those fabricated from fresh cells.

The efficiency of small-area perovskite-silicon tandem solar cells is already above 30%; however, there are few studies about large-area tandem cells. One main challenge for the upscaling of perovskite-silicon tandems is the non-uniformity of perovskites across large areas of tandem cells that can cause shunting, which becomes more serious when large-area tandems are fabricated via a solution process. Here, we demonstrate the fabrication of efficient large-area tandems on industry-compatible Czochralski-grown and chemically etched rough silicon wafers using a blading process. We employed a lithium fluoride (LiF) interlayer to significantly mitigate the shunting issue for large-area tandems when it is deposited on the hole transport layer side. The LiF interlayer decreases local current drains and improves interfacial contact at the buried perovskite interface. As a result, a stabilized power conversion efficiency of 25.1% is achieved for tandem devices with a large aperture area of 24 cm2.

Wide-bandgap (WBG) mixed-halide perovskites show promise of realizing efficient tandem solar cells but at present suffer from large open-circuit voltage loss and the mechanism is still unclear. Here we show that WBG perovskites with iodide–bromide compositions have an increased concentration of deep traps induced by iodide interstitials, which limits performance of WBG perovskite cells. We employ tribromide ions to suppress the iodide interstitial formation and thus reduce charge recombination in bladed WBG perovskite films of Cs0.1FA0.2MA0.7Pb(I0.85Br0.15)3. The 1-µm-thick opaque WBG perovskite solar cells have an efficiency of 21.9%, a small open-circuit voltage deficit of 0.40 V and a large fill factor of 83%. The efficiency of the best-performing monolithic perovskite–silicon tandem cell using this perovskite reaches 28.6%. The tribromide addition also suppresses light-induced phase segregation in WBG perovskites and thus enhance device stability. Encapsulated tandem cells maintain 93% of their initial efficiency after operation for 550 h. Efficient perovskite–silicon tandem solar cells with an efficiency of up to 28.6% are reported by employing tribromide ions to reduce charge recombination.

Select emerging solar cell technologies, ranging from very narrow screen-printed fingers to perovskite/silicon tandems, would benefit from a reduction of the height of the standard pyramidal texture of monocrystalline silicon wafers to below 1 mu m. However, fabricating such small surface features usually compromises the requisite low reflectance and high passivation quality. Through systematic design of experiments, we demonstrate that conventional alkaline-based wet-chemical etching processes can be tuned to produce dense, spatially homogeneous, and uniformly sized sub-micrometer pyramids. Precise texture size can be further controlled by adding potassium silicate to the texturing solution to effectively slow the pyramid growth rate and promote nucleation. With pyramid size distribution data-extracted from multiple atomic force microscopy images across each wafer-we demonstrate 16 nanotextures with average pyramid sizes ranging from 62 to 512 nm, with the largest having only 0.3% of its pyramids taller than 1 mu m. Six of the nanotextures exhibit light trapping and surface defect densities comparable to state-of-the-art microtextured wafers. The best nanotexture achieved an AM1.5G-weighted reflectance of 11.8% and a minority-carrier lifetime of 3.4 ms after passivation with amorphous silicon, demonstrating that smaller textures need not deteriorate solar cell performance.