Nucleation and crystallization control of perovskite films toward efficient perovskite photovoltaics

Abstract

Perovskite photovoltaics have advanced rapidly across single-junction, module-scale, and tandem architectures, yet further progress is increasingly constrained by insufficient control over nucleation and crystallization, which amplifies microstructural non-uniformity, defect-assisted nonradiative recombination, compositional gradients, and operational instability. Motivated by these challenges, this thesis develops nucleation/crystallization regulation strategies across multiple perovskite material systems and device formats, aiming to establish clear mechanistic links between film-formation dynamics and device losses across different perovskite systems, and to demonstrate practical performance improvements from the small-area rigid solar cell level to advanced device architectures.
First, a polarity-engineering strategy is introduced in a normal-bandgap formamidinium lead iodide system using a series of (Methylsulfonyl)phenethylammonium additives. By increasing the polarity of the additive, additive-precursor interactions in the intermediate stage are strengthened, the approach promotes direct nucleation and crystallization of the photoactive phase without participation of the non-photoactive phase, thereby improving crystallographic orientation and reducing defect formation. Beyond kinetic regulation, an unexpected mesoscopic dielectric-screening effect is identified: polar additives enriched at grain boundaries increase the local dielectric response, weaken Coulomb interactions between charged defects and carriers, and reduce defect-assisted carrier capture and ion migration. These coupled effects enable a champion single-junction device efficiency increased from 22.9% for the control device to 25.2%, and demonstrate significantly improved operational stability with over 93% of the initial power conversion efficiency maintained after 450 hours of continuous illumination. This strategy is further validated at the module level, where a large-area perovskite solar module with an active area of 70 cm² achieves a power conversion efficiency of 20.5%, substantially higher than the 16.5% obtained for the control module.
Second, the thesis extends nucleation and crystallization control to wide- and narrow-bandgap multi-component perovskites used for all-perovskite tandem architectures. In these compositions, a key limitation is not only the overall film-formation rate but also mismatched nucleation and crystallization kinetics among different compositions, which drives vertical compositional gradients and phase instability. To address this issue, an additive-design strategy guided by chemical hardness and softness is developed to harmonize coordination interactions and synchronize nucleation and crystal-growth dynamics across the components, thereby suppressing phase segregation and reducing nonradiative losses. Using difluoro(oxalato)borate for the wide-bandgap sub-cell and tetrafluoroborate for the narrow-bandgap sub-cell, the power conversion efficiencies of the corresponding single-junction devices are increased from 18.7% to 20.1% and from 21.6% to 23.3%, respectively. Based on these optimized sub-cells, the monolithic two-terminal tandem device achieves a certified efficiency of 30.3%, compared with 28.6% for the control device, and retains 92% of its initial efficiency after 1000 h of maximum-power-point operation. When applied to flexible devices, the tandem achieves a power conversion efficiency of 28.2%, with a certified value of 28.0%, compared with 25.2% for the control flexible tandem, and maintains 95.2% of its initial efficiency after 10,000 bending cycles at a radius of 2 mm.
Overall, this thesis shows that rational regulation of nucleation and crystallization—implemented through polarity-driven kinetic control coupled with dielectric screening, and through chemical-hardness-guided additive selection to synchronize multi-component kinetics—provides an effective route to improve efficiency and operational robustness in both single-junction and tandem perovskite photovoltaic technologies, and is further demonstrated in large-area modules and flexible devices.

Date of Award	18 Jul 2026
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Bencan Tang (Supervisor), Ziyi Ge (Supervisor), Hainam Do (Supervisor) & Darren Walsh (Supervisor)