Florian Schindler

Long‐term reliability of high‐efficiency tunnel oxide passivated contact (TOPCon) and silicon‐heterojunction (HJT) modules seem threatened by ultraviolet light‐induced degradation (UVID), yet the kinetics and triggers of the defect mechanisms remain poorly understood. We systematically investigate UVID in unencapsulated industrial solar cells under variations of UV spectrum, intensity, temperature, and concurrent visible illumination (VIS) and correlate resulting losses with hydrogen redistribution measured by ToF‐SIMS. Short‐wavelength UV photons strongly enhance UVID and drive near‐surface defect formation, whereas elevated cell temperatures during exposure substantially suppress degradation. For a fixed exposure time, the defect generation scales linearly with cumulative UV photon dose, but the net UVID amplitude depends critically on the accumulated thermal budget. Under combined UV + VIS illumination near‐outdoor conditions, although at open contacts, UVID is almost completely suppressed, indicating that continuous carrier injection promotes repassivation and prevents stable defect buildup. Post‐UV dark storage induces additional metastable degradation in the TOPCon group, which, like the initial UVID, is reversible by visible light soaking at elevated temperature. Our results substantiate hydrogen‐mediated interface changes as the most likely key driver of UVID and highlight that accelerated UV tests must account for spectral shape, temperature history, and concurrent VIS illumination to reproducibly determine UVID in field performance.

Increasing the thickness of perovskite thin film absorbers allows for enhanced photo absorption, which increases the current and performance of the solar cells. In multijunction devices, thickness optimization is critical to achieve current matching between subcells, depending on the bandgap combination. However, maintaining film quality while balancing charge transport and recombination becomes more challenging as thickness increases. Herein, we investigate thickness limitations of wet‐chemically processed 1.56 eV mixed cation mixed halide perovskites as middle cell in monolithic perovskite/perovskite/silicon triple‐junction solar cells. It is found that Cs _0.05 (FA _0.90 MA _0.10 ) _0.95 Pb(I _0.95 Br _0.05 ) ₃ perovskite shows a decrease in performance for thickness >450 nm. Substituting bromide with chloride (Cl ⁻ ) in the composition allows to increase layer thickness up to ∼700 nm without sacrificing fill factor (FF) and open‐circuit voltage ( V _OC ) _. The Cl‐substituted absorbers show larger grain size, less nonradiative recombination loss, higher carrier lifetime, and mobility as evidenced by steady‐state and transient photoluminescence, and optical pump/terahertz probe spectroscopy measurements. Thick Cl‐substituted absorbers enhance performance up to 20% in 1 cm ² semitransparent single‐junction devices. By integrating the ∼700 nm perovskite as middle cell in a perovskite/perovskite/silicon triple‐junction device, an efficiency of 23.4% with a short circuit current density of 9.6 mA/cm ² , a FF of 80.5%, and a V _OC of 3026 mV is achieved.

Perovskite–silicon triple-junction photovoltaics offer efficiency gains beyond dual-junction devices but at the expense of added complexity ¹ . Here we address two key bottlenecks in perovskite–silicon-based triple-junction solar cells: reduced open-circuit voltage ( V _OC ) in the wide-bandgap (WBG) top cell and limited photocurrent generation in the middle cell ^1,2 . A non-volatile additive, 4-hydroxybenzylamine (HBA), regulates WBG perovskite crystallization and passivates defects, promoting oriented growth and suppressing non-radiative recombination. Together with improved energy-level alignment, this yields V _OC s of up to 1.405 V and enhanced stability. To overcome the current limitations in the middle cell, a three-step deposition strategy enables the formation of thick, low-bandgap perovskite absorbers while preserving microstructural integrity and enhancing electron extraction. Also, low-refractive-index SiO _x -nanoparticles (SiO _x -np) that accumulate in the front valleys of the textured silicon bottom cell act as an optical middle reflector, enhancing light absorption in the middle cell. These advances are then combined in 1-cm ² perovskite–perovskite–silicon devices, achieving a certified efficiency of 30.02%.

Characterization of perovskite–silicon (Pero/Si) tandem solar cells in an industrial environment is hampered by several challenges. First, the monolithic series connection of the two subcells and the fact that the entire stack shares only two electrical terminals make it impossible to probe each subcell independently. Second, the perovskite absorber's metastability—most notably ion migration—introduces additional, often slow, time‐dependent effects. Together with the industry's requirement for high throughput, these factors complicate accurate, high‐speed characterization. In this work we propose a concept to acquire I–V data for tandem solar cells from light‐emitting diode (LED)‐based solar simulators, where we acquire an approximation of the external quantum efficiency from LED‐based measurements before conducting an I–V measurement with an adjusted LED illumination spectrum. We present results on a reference III/V and different Pero/Si solar cells. We model ion migration in perovskite subcells, which allows for assessing preconditioning and transient effects in I–V cell measurements. We recommend a short preconditioning under light to stabilize the scan time dependence and show the potential for transfer between industrial and lab conditions. Finally, we showcase concepts of camera‐based luminescence measurements for inline analysis. Specifically, we show a line‐scan photoluminescence approach, a fast electroluminescence (EL) imaging approach based on parallel data acquisition with two cameras, and an EL concept based on the application of one RGB camera.

Monolithic two‐terminal perovskite‐based multijunction solar cells are considered as the next generation technology in the photovoltaic market, thanks to their high power conversion efficiency at potentially low production costs. In these structures, an interlayer is required for subcell interconnection. Commonly used recombination layers are based on scarce and expensive materials such as gold or indium. Developing alternative candidates without compromising device performance is therefore crucial for the future of such multijunction technologies. Herein, low‐temperature sputtered zinc tin oxide (ZTO) is employed as an indium‐free recombination layer between two perovskite subcells. ZTO is deposited using scalable in‐line sputtering. Slight zinc doping of tin oxide is needed to enable the DC sputtering from a rotary target. Employing ZTO results in improved device performance compared to the reference devices with indium tin oxide recombination layer, deposited via a lab‐type sputtering tool. Perovskite/perovskite/silicon triple‐junction and all‐perovskite tandem solar cells show increased open‐circuit voltages by ≈60 and ≈30 mV, respectively. The work showcases that ZTO can be sputtered in a non‐destructive and scalable manner in different perovskite‐based multi‐junction technologies.

Reducing charge carrier transport losses, improving selectivity, and minimizing nonradiative recombination are essential for enhancing the efficiency and stability of perovskite/silicon tandem solar cells. We used a hybrid two-step perovskite deposition method that is compatible with industry-standard textured silicon, incorporating a perovskite surface treatment based on 1,3-diaminopropane dihydroiodide. The interaction of this molecule with the perovskite surface increased the majority charge carrier concentration at the electron-selective contact, which reduced interfacial recombination. Simultaneously, this field-effect passivation increased the electron concentration across the entire intrinsic perovskite absorber, which increased conductivity and reduced transport losses. Combined, this yields high-performance, fully textured perovskite/silicon tandem solar cells, achieving a 1-sun AM1.5G conversion efficiency of 33.1% with an open-circuit voltage of 2.01 volts and an extended outdoor stability in the Red Sea Coast.

Light‐ and elevated‐temperature‐induced degradation (LeTID) has been the most discussed degradation phenomenon during the late p ‐type passivated emitter and rear cell (PERC) era. It is important to investigate whether similar issues affect the new generation of n ‐type tunnel oxide passivating contacts (TOPCon) solar cells. This study focuses on the temporary recovery (TR), the reverse reaction to the degradation reaction. TR has been key to understanding LeTID in p ‐type Si. Its existence is demonstrated and reported in n ‐type silicon solar cells for the first time. Further, the repeatability of the degradation‐TR‐cycle is shown and other effects unique to TR are demonstrated, such as a negative activation energy, and the TR rate constant scaling superlinearly with Δ n . With TR as a tool, LeTID defects are identified to be present already after the fast‐firing process. Such defects, if initially present, can have a multitude of effects. First, they lower the initial efficiency. Second, this might lead to the development of processes that are indirectly based on TR, enhancing the efficiency but concurrently leading to stronger degradation. Furthermore, it is imperative to exercise caution and to include the potential for TR when devising stability tests. Finally, it is demonstrated that strategies to mitigate LeTID in p ‐type also work for n ‐type.

Perovskite–silicon triple-junction photovoltaics offer efficiency gains beyond dual-junction devices, but at the expense of added complexity. Here, we address two main challenges in perovskite-silicon-based triple-junction solar cells: reduced open-circuit voltage in the wide-bandgap top-cell and limited current density in the middle-cell. Additive engineering with 4-hydroxybenzylamine modulates the crystallization dynamics of the top-cell absorber and suppresses bulk recombination, enabling open-circuit voltages up to 1.405 V. The three-step-manufactured lead-halide middle-cell absorbers result in an increasing thickness and a reduced bandgap, thereby boosting the current density. Low-refractive-index SiOx nanoparticles accumulated in the front valleys of the textured silicon bottom-cell act as a middle-reflector, enhancing light absorption in the middle-cell. These innovations are then combined in 1-cm2 perovskite-perovskite-silicon devices, reaching a steady-state efficiency of 30.5%.