Maryamsadat Heydarian

Perovskite-based triple-junction solar cells offer a theoretical efficiency potential exceeding 47%. As an emerging photovoltaic technology, recent research has focused on optimizing the top, middle, and bottom subcells, as well as the recombination layers between the subcells.

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.

Employing indium-based transparent conductive oxides (TCO) such as indium tin oxide (ITO) in silicon solar cells is already a hurdle due to the scarcity of indium for the photovoltaic community. This is even more challenging in perovskite/silicon multijunction solar cells where TCO layers are necessary for multiple applications beyond transparency and lateral carrier transport. Development of perovskite/perovskite/silicon triple-junction solar cells is a relatively new research focus. It is important to consider this criticality of the raw materials used during the design and development phase. In this work, we successfully replaced all four ITO layers used in our perovskite/perovskite/silicon triple-junction solar cell with an indium-free material. We mainly used zinc-doped tin oxide (ZTO), while for the silicon bottom cell’s front and rear contacts an interfacial layer of aluminum-doped zinc oxide (AZO) was used to ensure low contact resistance/efficient vertical transport to the silicon thin films. To replace the ITO top TCO of the perovskite top cell, a ZTO material with lower ZnO fraction was used to achieve a lower sheet resistance/more efficient lateral transport. With this, we present the first fully indium-free silicon-based triple-junction solar cell with no efficiency penalty.

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%.

We report a two-step thermal evaporation–close space sublimation deposition method for tunable bandgap lead halide perovskites with single junction solar cell efficiencies exceeding 20%. These absorbers are integrated into perovskite–silicon tandem solar cells with stabilized efficiencies of >29%.

In recent years, the development of perovskite/perovskite/silicon triple junction solar cells has received considerable attention, aiming to exceed the efficiency of perovskite/silicon dual junction solar cells. Various challenges must be addressed to reach these efficiencies and justify the additional complexity. This article outlines a simulation‐based roadmap for improving the structure of these cells. It discusses critical issues and estimates potential improvements for perovskite/perovskite/silicon solar cells based on device architectures developed at Fraunhofer ISE and EPFL. The article describes potential challenges related to thickening the middle perovskite absorber to achieve current matching. It explains the observed losses in fill factor in the top cell with a high bandgap, which arise from an insufficient hole barrier caused by unfavorable valence‐band alignment between the perovskite and the electron transport layer. These aspects are examined through numerical device simulations.

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.

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%.

Perovskite‐based triple‐junction solar cells have recently gained significant attention and are rapidly developing, thanks to the insights gained from the advancement in its dual‐junction counterparts. However, employing perovskite materials in multijunction solar cells with more than two junctions brings new challenges that have not yet been addressed. One aspect is the possibility of reverse bias breakdown of perovskite subcells during operation of the triple–junction device. This is more relevant for triple‐junction solar cells because a higher reverse voltage might drop at perovskite subcells compared to the case of dual‐junction solar cells. Herein, the breakdown voltages of the two perovskite subcells in perovskite/perovskite/silicon triple‐junction solar cells are determined by progressively increasing the reverse bias applied to the subcells in a single‐junction architecture during current–voltage measurements and monitoring the appearance of shunts using illuminated lock‐in thermography measurements. Furthermore, to analyze the effect on the final triple–junction solar cell, the triple‐junction device is brought in different current limitation conditions. It is shown that the subcell breakdown can happen during the operation of the triple‐junction solar cell, especially for the case where the perovskite top cell is limiting the overall current of the device. This effect is less severe when the middle perovskite cell limits the current due to the absence of a direct contact with the silver metallization which has shown to be the major degradation site during reverse biasing of perovskite solar cells. Finally, there is no concern regarding breakdown of the silicon bottom cell due to the higher breakdown voltage of silicon compared to perovskite.

Monolithic perovskite-based triple junction solar cells have the potential to surpass the power conversion efficiency (PCE) limits of single and dual-junction solar cells.