Researchers at the Huaneng Renewables Corporation, Nanjing University of Posts & Telecommunications, Thermal Power Research Institute and Zhejiang University have developed a molecular surface doping strategy that enables high-performance inverted perovskite solar cells (IPSCs) to be fabricated under high-humidity ambient conditions, addressing one of the key bottlenecks for scalable manufacturing.
While IPSCs have reached certified power conversion efficiencies (PCEs) of up to 27%, their fabrication typically relies on controlled environments such as nitrogen-filled gloveboxes and the use of anti-solvents. Processing in air - especially at relative humidity (RH) above 50% - introduces severe challenges. Moisture accelerates crystallization and promotes hydration-induced phase transitions, leading to structural degradation and a high density of defects. These defects are concentrated at surfaces and interfaces, where their density can be nearly two orders of magnitude higher than in the bulk. In particular, excess p-type defects form at the perovskite/air interface, weakening the n-type surface contact required for efficient IPSCs and increasing nonradiative recombination losses.
To address this, the researchers introduced pyridine-2,6-diamide (PDBA) as an n-type semiconductor for surface modification. The molecule combines a pyridine ring with two amide groups, enabling strong coordination with uncoordinated Pb²⁺ ions on the perovskite surface.
This interaction plays several roles simultaneously:
- Passivates undercoordinated Pb²⁺ defect sites.
- Suppresses the formation of additional p-type defects at the surface.
- Enhances n-type character at the perovskite interface.
- Reduces nonradiative recombination by improving carrier lifetimes.
The electron-donating nature of both the pyridine ring and amide groups enables effective Lewis base interactions with the perovskite lattice, stabilizing the surface under humid conditions.
Using this approach, the team fabricated IPSCs in ambient air with approximately 60% relative humidity and achieved a champion PCE of 22%. This represents a significant step toward eliminating the need for controlled environments during device fabrication.
Beyond efficiency, the devices also demonstrated strong operational stability. Under ISOS testing protocols, they retained 93% of their initial efficiency after 800 hours under ISOS-L-2I conditions. In addition, extended stability was observed under ISOS-D-1I testing for over 1700 hours.
The study highlights that controlling surface defect chemistry rather than relying solely on environmental control can enable high-quality perovskite films even under challenging ambient conditions. By introducing multifunctional Lewis-base molecules like PDBA, it becomes possible to simultaneously passivate defects and tune interfacial energetics.
This molecular n-doping strategy offers a practical pathway for fabricating efficient and stable IPSCs in high-humidity air, bringing perovskite photovoltaics closer to industrial-scale production.
