‘New World Record’ For All-Perovskite Tandem Solar Modules

• Nanjing University researchers have announced achieving 24.5% all-perovskite tandem solar module efficiency  
• Achieved on an aperture area of 20.25 cm², they claim it to be the world's highest efficiency for this category  
• They used glycinamide hydrochloride to homogenize crystallization process and also passivate the buried perovskite interface 

Researchers at China's Nanjing University have achieved what they call is a new world record for power conversion efficiency of large-area all-perovskite tandem solar modules. The team led by Professor Tan Hairen claims certification for its 24.5% efficiency from Japan Electrical Safety and Environment Technology (JET).   

The team at the Nanjing University's School of Modern Engineering and Applied Science says it achieved the high efficiency on an aperture area of 20.25 cm². Its Voc is 2.157 and fill factor (FF) 77.5.   

According to the team, "The world record efficiency of perovskite stacked modules has laid the technical foundation for the mass production and commercial application of all-perovskite stacked cells." 

Hairen and team previously reported small-area all-perovskite tandem cell efficiency of 28%, using grain surface interface passivation strategy. They further achieved a large-area laminated certified efficiency of 21.7% through mass-produced preparation technology.  

Aiming for industrial production of these modules, the team says current large-scale technology development focuses on conventional bandgap perovskite films. However, these lead to fast crystallization, leading to uneven film formation that doesn't work for mass production. It can cause a large-number of defects at the bottom interface of the lead-tin perovskite.  

The team's focus was on controlling crystallization which it achieved by adding a multifunctional zwitterionic buffer-glycinamide hydrochloride to the precursor solution.  

According to the researchers, "Glycinamide hydrochloride can form hydrogen bonds between perovskite organic cations and solvents, and form complexes with metal halides in the perovskite precursor, inhibiting and delaying solvent evaporation during the perovskite crystallization process."  

They add, "The crystallization rate of perovskite greatly extends the preparation window time for large-area film formation of perovskite films, achieving large-area and uniform preparation of lead-tin perovskite films."  

High solubility of glycinamide hydrochloride in the precursor solution can induce it to spontaneously aggregate at the bottom interface of the perovskite film. This, explains the team, reduces the defect density at the bottom interface thereby greatly improving the carrier lifetime of the perovskite film. 

The team's research is now published in the scientific journal Science with the title Homogeneous crystallization and buried interface passivation for perovskite tandem solar modules.  

The efficiency level achieved has also been included in the Solar Cell Efficiency Tables (Version 63) collated by an international research group led by Professor Martin Green.