Kerem Artuk

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%.

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.

Screen-printed Ag metallization on ITO enables perovskite/silicon tandems of 34.0% on 1 and 4 cm ² and of 31.3% on 54 cm ² , while Ag–Cu pastes cut silver use at only a minor efficiency loss.

In this work, the effects of luminescent coupling (LC) on the external quantum efficiency (EQE) of perovskite‐silicon tandem (PST) solar cells are quantified by means of monochromatic transient photocurrent measurements and comprehensive optoelectronic simulations that take into account both optical and electrical coupling of the subcells. It is shown that, at short wavelengths, a similar response results from both LC and silicon bottom‐cell shunts. The two contributions can be discriminated and quantified based on bias voltage and light intensity‐dependent measurements. Such measurements were conducted on state‐of‐the‐art PST cells and agree well with the behavior predicted by the simulations. For the case of polychromatic EQE simulations, a quenching of the LC effects with decreasing concentration of mobile ions is found, which is explained in terms of ion‐modulated recombination via bulk defects.

Inverted perovskite solar cells face performance limitations due to non-radiative recombination at the perovskite surfaces in devices, including functional layers. Advanced characterization and density functional theory reveal that phosphonic acids passivate perovskite surface defects, while piperazinium chloride mitigates interface recombination by improving energy level alignment, introducing a field effect, and homogenizing the surface. Together, the quasi-Fermi level splitting of the perovskite is homogeneously increased by ca. 100 mV. This enables two-terminal perovskite-on-silicon tandems to achieve a certified open-circuit voltage of 2 V for a 1 cm² device and high performance in excess of 31%. The scalability of the passivation is furthermore demonstrated with homogeneously passivated devices reaching certified efficiencies of 28.9% for an active area of 60 cm².

Perovskite–TOPCon² tandem solar cells reaching 31.3% efficiency on front-textured devices, enabled by an optimized AlO_x-based hydrogenation process that provides high passivation quality.

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%.

Inverted perovskite solar cells face performance limitations due to non-radiative recombination at the perovskite surfaces in devices, including functional layers. Advanced characterization and density functional theory reveal that phosphonic acids passivate perovskite surface defects, while piperazinium chloride mitigates interface recombination by improving energy level alignment, introducing a field effect, and homogenizing the surface. Together, the quasi-Fermi level splitting of the perovskite is homogeneously increased by ca. 100mV. This enables two-terminal perovskite-on-silicon tandems to achieve a certified open-circuit voltage of 2V for a 1 cm² device and high performance in excess of 31%. The scalability of the passivation is furthermore demonstrated with homogenously passivated devices reaching certified efficiencies of 28.9% for an active area of 60 cm².

Cesium‐formamidinium lead iodide (Cs_xFA_1‐xPbI₃) perovskites are a promising methylammonium‐free alternative for efficient single‐junction solar cells. However, they have not been fully explored by vapor‐phase deposition techniques. Herein, a template‐assisted approach is demonstrated for the growth of Cs_xFA_1‐xPbI₃ perovskite films using pulsed laser deposition (PLD) from a single‐source target of mixed precursors. Implementing a lead iodide (PbI₂) + Cs_xFA_1‐xPbI₃ tailored template, phase‐pure Cs_xFA_1‐xPbI₃ films with uniform coverage on both planar and textured substrates are achieved. Compositional analysis via X‐ray fluorescence confirms near‐stoichiometric transfer of the inorganic cations (Cs/Pb), with identical Cs_0.2FA_0.8PbI₃ composition and a bandgap of 1.58 eV achieved in templated and non‐templated films. However, the presence of the template proves essential for attaining phase‐pure films in the photoactive cubic (α‐) phase. Proof‐of‐concept solar cells fabricated with templated‐PLD α‐Cs_xFA_1‐xPbI₃ achieve an efficiency exceeding 12.9% on 0.1 cm² area devices without the employment of passivation approaches. Additionally, increasing deposition rates does not alter the phase, morphology, or optoelectronic properties of the templated films on textured substrates, indicating the robustness of this methodology. The compositional control of PLD for Cs‐FA‐based perovskites is showcased, and template‐assisted growth is demonstrated as a reliable pathway to high‐quality reproducible perovskite films.