Researchers from China's Hebei University of Technology, Fudan University, Fuyang Normal University, Chinese Academy of Sciences (CAS), Macau University of Science and Technology, Kunming University of Science and Technology and France's CNRS have reported an innovative passivation strategy that is said to enable record power conversion rates and enhanced operational longevity of single junction and tandem perovskite solar cells (PSCs).
The team has developed this innovative strategy to address the issue of interfacial trap-assisted nonradiative recombination, which has been known to hinder the performance of perovskite-based photovoltaic technologies. The new passivator is identified as L-valine benzyl ester p-toluenesulfonate (VBETS) and using it under optimal conditions yielded PSCs that achieved a power conversion efficiency (PCE) of 26.28%.
The need for this passivation system arose from inherent challenges faced by PSCs, particularly their susceptibility to ion migration and the prevalence of deep-level defects. These issues contribute to energy losses and reduced durability over time—a significant barrier to the wide adoption of this promising solar technology.
The new approach revolves around the design of organic ammonium salts to passivate surface defects effectively. This technology hinges on adjusting the number of hydrogen atoms and managing steric hindrance via molecular engineering. By employing VBETS, which efficiently neutralizes both positively and negatively charged defects on the perovskite surface, the researchers mitigated the energy loss typically experienced at the interface.
According to the authors of the study, the defect passivation effect of cations, including VBETS, is influenced significantly by the balance between the number of hydrogen atoms present and the size of the cations used. Testing revealed this balance is pivotal for enhancing the overall efficiency of these solar cells.
The VBETS passivator also demonstrated substantial improvements concerning long-term operational stability. Under continuous light exposure conditions, VBETS-modified single-junction PSCs were able to retain about 90.8% of their initial efficiency after 4,000 hours, overshadowing control devices which only maintained around 70.9% efficiency. Such stability improvements could be pivotal for the widespread adoption of solar technologies.
The large-area PSC modules created using this technology reported efficiencies of 21.00%, showcasing scalability and commercialization potential.
When combining the results from various experimental methods, analysis pointed to significant reductions in defect density and nonradiative recombination losses within the modified PSCs. These enhancements were confirmed through diverse characterization techniques such as photoluminescence and transient photocurrent measurements.
The research concludes by emphasizing the transformative impact of VBETS and its design strategy, which might guide future developments aimed at refining the efficiency and reliability of perovskite solar technology. Further study is needed to fully leverage the potential of these materials and to broaden their applicability across different solar technologies.
