Researchers from Shanghai Jiao Tong University have developed a new method to produce halide-homogeneous wide-bandgap (WBG) perovskite films using a blade-coating technique, significantly improving the efficiency and stability of perovskite-organic tandem solar cells.
In conventional WBG perovskite films, the markedly different crystallization rates of bromide (Br⁻) and iodide (I⁻) ions often lead to vertical halide inhomogeneity - Br-rich layers forming near the surface and I-rich regions accumulating near the bottom. This uneven distribution causes considerable open-circuit voltage (VOC) losses and limits device efficiency. To tackle this, the team systematically investigated the vertical halide distribution in large-area films fabricated via gas-quenching blade coating. They then introduced a hydrogen-bonding donor solvent (HBDS), formamide (FM), into the standard N,N′-dimethylformamide (DMF)/dimethyl sulfoxide (DMSO) solvent mix. With its relatively high acceptor number (AN), formamide forms stronger hydrogen bonds with halide ions - especially with the electron-rich Br⁻- and effectively modulates the crystallization kinetics of the two halide species.
Among the three hydrogen-bonding solvents tested, formamide exhibited an optimal interaction strength that slowed the crystallization of Br-rich phases. This adjustment enabled the synchronized crystallization of the mixed Br⁻/I⁻ perovskite phase, yielding vertically homogeneous WBG films with a bandgap of 1.86 eV. The resulting perovskite solar cells achieved an impressive power conversion efficiency (PCE) of 18.9% and a VOC of 1.41 V.
Building on these advances, the researchers fabricated perovskite-organic tandem solar cells (TSCs) that delivered a PCE of 26.3%, with a certified value of 25.6%. Even after continuous illumination for 1000 hours, the devices retained 92% of their initial efficiency, underscoring their excellent operational stability.
This study highlights a scalable approach to producing halide-compositionally uniform WBG perovskite films through hydrogen-bonding modulation. By synchronizing halide crystallization dynamics, it opens a practical route toward large-area, high-efficiency perovskite-organic tandem devices and brings the technology closer to industrial application.
