Julien Hurni

Zinc phosphide () shows great promise for next‐generation photovoltaics made of earth‐abundant elements. To date, the poor crystal quality is limiting conversion efficiency to 4.4% for heterojunction and to 6% for Schottky junction solar cell. This work presents the fabrication and characterization of /InP solar cells with a new record efficiency of 8%. The material quality is significantly improved by using selective area epitaxy (SAE) in conjunction with a post‐growth annealing. The combination of current–voltage (J–V) measurements and electron beam induced current (EBIC) mapping, alongside with optical and electrical simulations, outline the impact of the SAE pattern dimensions on the device performances. A decrease in the opening area fraction is associated with an increase in the V _OC and a decrease in the J _SC . Our results suggest that the degradation of the V _OC for large openings is predominantly attributable to the presence of misfit dislocations at the heterojunction interface. On the other hand, the reduced J _SC for small openings is associated with a smaller electron diffusion length, which is attributed to the current crowding effect. Finally, the device's stability under outdoor testing over a year is demonstrated.

For several classes of crystalline silicon (c-Si) photovoltaic (PV) cells, such as silicon heterojunction (SHJ) or tunnel oxide passivated contact (TOPCon), an obstacle to producing them at the terawatt scale is the use of silver in their contacts. One promising alternative is copper, which is often implemented in combination with a barrier material to prevent degradation via copper diffusion. But because there may be cases where the barrier is locally absent between copper and Si (caused by fabrication imperfections such as dust), it may be desirable to design silicon-based cell layers that are themselves resistant to copper-induced degradation. Here, we study how the crystallinity of n-type polysilicon layers (like those used at the rear of a TOPCon cell) affects their susceptibility to copper-induced degradation. We study simple, symmetric samples consisting of sputtered copper thin films on flat n-type polysilicon / silicon oxide (poly-Si(n) / SiOx) passivating contact stacks. After annealing the samples at 200°C for 30 minutes in nitrogen, the passivation is ruined for samples whose poly-Si crystalline fractions are high, while more amorphous poly-Si(n) show little to no change in passivation. The passivation is also ruined for a sample with highly crystalline poly-Si(n) that is >1.5x thicker than the more amorphous poly-Si(n). This study may aid in the development of poly-Si thin films that, combined with a diffusion barrier layer, provide the highest protection against copper-induced degradation in scalable, copper-metallized PV cells.

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%.

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.

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.

This work investigates the potential of nanocrystalline silicon carbide (nc-SiC) films as transparent passivating contacts for high-efficiency solar cells. A plasma-enhanced chemical vapor deposition process for high hydrogen radical density was developed to fabricate nc-SiC films. The influence of phosphorus (P) doping and thermal treatment on the structural, compositional, and electrical properties of these films was investigated. Increased doping reduced the contact resistance but also negatively affected the open circuit voltage ($iV_{\text{oc}}$). We identified a set of parameters that provided a compromise between conductivity and passivation, resulting in a maximum $iV_{\text{oc}}$ of 708 mV on textured surfaces with a contact resistance of around 100 $\mathrm{m}\mathrm{\Omega }\mathrm{c}\mathrm{m}^{2}\,$. In addition, nc-SiC exhibited superior ultraviolet transparency compared to poly silicon (poly-Si) and crystalline silicon (c-Si), with an absorption coefficient of $3\times 10^{5}\; \text{cm}^{-1}$ at 350 nm, lower than the typical $1\times 10^{6}\; \text{cm}^{-1}$ for poly-Si and c-Si.