Juliane Borchert

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.

Molecular engineering of evaporated Me‑4PACz and 2PACz SAMs reveals the link between structure to interface quality and tandem performance. Mitigating SAM disorder enables 32.2% efficient fully textured perovskite/silicon tandems.

The conformal coating of perovskites on textured silicon for tandem solar cells requires scalable deposition methods, for which hybrid vacuum-solution processing, using an evaporated inorganic scaffold (Pb/Cs halides) followed by solution conversion, is promising. Yet multisource coevaporation of the scaffold, as commonly used for lab-scale devices, is complex and costly to implement at an industrial scale. Here, we investigate sequential single-source evaporation of the inorganic scaffold as an industrially viable alternative. Five sequentially evaporated scaffold stacks were compared to a coevaporated reference. Despite differences in PbI₂ conversion, halide distribution, and morphology, all showed similar single-junction device power conversion efficiencies (∼19%). The best scaffold (a PbI₂/CsBr/PbI₂/CsBr/PbI₂ stack) achieved 28.4% in perovskite/silicon tandems without molecular additives, matching the coevaporated reference (28.3%). This work demonstrates that sequential deposition of the inorganic scaffold offers a scalable route to high-efficiency tandems.

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.

Solvent-free perovskite solar cells offer scalable processing and excellent large-area homogeneity. Here, we investigated the influence of hole transport layers on structural evolution and device performance of sequentially evaporated perovskites.

Functional-group engineering reveals distinct passivation mechanisms at the perovskite/C ₆₀ interface, enabling the rational design of molecules that balance recombination suppression, device efficiency, and operational stability.

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.

Co-evaporation enables solvent-free route for perovskite solar cell fabrication. However, it presents challenges, such as substrate dependence and non-linear FAI evaporation, which might limit systematic studies and reproducibility.

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.