Shuaifeng Hu

Abstract:

Substantial VOC loss and halide segregation in wide-bandgap (WBG) perovskite sub-cells pose significant challenges for advancing all-perovskite tandem solar cells (APTSCs). Regarding this, one of the most impactful developments is the application of hole-selective self-assembled monolayers (SAMs), leading to the advancement in APTSC technology. However, SAMs with poor polar-solvent resistance would be inevitably delaminated from substrates during perovskite precursor coating, remaining great challenge in achieving a complete SAMs coverage with derivatization issues, e.g. defective perovskite and considerable interface energy loss. Here, we introduced an in-situ molecular compensation strategy to address the inherent flaw of SAMs within WBG perovskites via incorporating 5-ammonium valeric acid iodide (5-AVAI). The larger-dipole 5-AVAI spontaneously accumulates toward the buried interface to compensate the SAMs-deficient sites when depositing WBG perovskite, effectively minimizing interfacial energy loss. Simultaneously, amphoteric 5-AVAI with amino and carboxyl groups can compensate the defects at grain boundaries for solid passivation. Consequently, a champion efficiency of 20.23% with a record VOC of 1.376 V was realized on WBG devices, enabling an efficiency of 28.9% for the APTSCs. Encouragingly, the tandems showed good operational stability and retained 87.3% of their efficiency after 800 hours of tracking.

Abstract:

Narrow-bandgap tin and mixed tin-lead halide perovskites are attracting growing interest for optoelectronic applications, yet the difficult-to-control crystallization process has hindered their development. Although additive engineering has effectively improved film formation, the fundamental origins of their distinct crystallization behavior remain less explored. Here, through direct comparison with Pb counterparts, we investigate the pre-crystallization stages of Sn-based perovskite precursor solutions through complementary structural characterizations. We show that Sn precursors are intrinsically more reactive and sensitive to their chemical environment, exhibiting poorer colloidal stability compared to Pb and a strong inherent tendency to agglomerate. These findings explain their narrower processing window, where small variations in solution chemistry strongly affect nucleation and crystallization dynamics. To fabricate high-quality tin-based perovskite through solution methods, we highlight the importance of controlling the often-overlooked pre-crystallization stages, though, for example, rational solvent and additive designs. Overall, we provide fundamental insights into precursor solution chemistry and establish pre-crystallization engineering as a key strategy for overcoming long-standing limitations in thin-film fabrication, particularly in light of the field's rapid progression toward large-scale, sustainable, and solvent-conscious manufacturing.

Abstract:

Narrow‐bandgap tin and mixed tin–lead halide perovskites are attracting growing interest for optoelectronic applications, yet the difficult‐to‐control crystallization process has hindered their development. Although additive engineering has effectively improved film formation, the fundamental origins of their distinct crystallization behavior remain less explored. Here, through direct comparison with Pb counterparts, we investigate the pre‐crystallization stages of Sn‐based perovskite precursor solutions through complementary structural characterizations. We show that Sn precursors are intrinsically more reactive and sensitive to their chemical environment, exhibiting poorer colloidal stability compared to Pb and a strong inherent tendency to agglomerate. These findings explain their narrower processing window, where small variations in solution chemistry strongly affect nucleation and crystallization dynamics. To fabricate high‐quality tin‐based perovskite through solution methods, we highlight the importance of controlling the often‐overlooked pre‐crystallization stages, though, for example, rational solvent and additive designs. Overall, we provide fundamental insights into precursor solution chemistry and establish pre‐crystallization engineering as a key strategy for overcoming long‐standing limitations in thin‐film fabrication, particularly in light of the field's rapid progression toward large‐scale, sustainable, and solvent‐conscious manufacturing. A comparative NMR/SAXS study of lead‐ and tin‐based perovskite precursor solutions reveals fundamental differences in reactivity, environmental sensitivity, and colloidal stability. Tin systems show weaker colloidal stability, enhanced agglomeration, and strong solvent dependence. We provide the first detailed description of the pre‐crystallization stages governing tin halide precursor chemistry.

Abstract:

Vacuum-based deposition is a scalable, solvent-free industrial method ideal for uniform coatings on complex substrates. However, all vacuum-deposited perovskite solar cells fabricated by thermal evaporation trail solution-processed counterparts in efficiency and stability due to film quality challenges, necessitating advancement and improved understanding. Here, we report a co-evaporation route for 1.67-eV wide-bandgap perovskites by introducing a PbCl2 co-source to optimize film quality. We promote perovskite formation with pronounced (100) “face-up” orientation and deliver a certified all vacuum-deposited solar cell with 18.35% efficiency (19.3% in the lab) for 0.25-cm2 devices (18.5% for 1-cm2 cells). These cells retain 80% of peak efficiency after 1,080 hours under the ISOS-L-2 protocol. Leveraging operando hyperspectral imaging, we provide spatiotemporal spectral insight into halide segregation and trap-mediated recombination, correlating microscopic luminescence features with macroscopic device performance while distinguishing radiative from non-ideal recombination channels. We further demonstrate 27.2%-efficient 1-cm2 evaporated perovskite-on-silicon tandems and outdoor stability of all vacuum-deposited tandems in Italy, retaining ~80% initial performance after 8 months.

Abstract:

<jats:p>This study pioneers a solvent-additive cascade strategy to achieve crystallographically homogenous perovskite films, breaking the efficiency–stability trade-off by harnessing facet-dependent properties for record performance.</jats:p>