Scientists from the University of Konstanz in Germany, Quaid-i-Azam University and Kohsar University Murree in Pakistan and Huazhong University of Science and Technology in China have fabricated an inverted perovskite solar cell with a passivation technique utilizing a mixed solvent vapor annealing method based on ethylenediamine (EDA).
The team managed to show how simple passivation can improve both the performance and operational stability of a perovskite solar cell. The scientists said EDA has been used in previous research projects to suppress the defect states in different kinds of perovskite. However, the exact way that EDA contributes to the morphology, defect passivation and optoelectronic properties of perovskite films was unclear.
The team applied their EDA passivation technique via solvent vapor annealing followed by annealing at 90 C for 30 minutes to a film based on a methylammonium lead iodide (MAPbI3) lead-halide perovskite. They claimed they were able to achieve enhanced crystallinity and a densely packed film morphology featuring larger grains than a non-passivated reference film.
The researchers annealed the film under a vacuum chamber after spin coating and then placed it in a controlled EDA vapor environment with a concentration of 0.06 wt.%. The EDA interacted with the perovskite surfaces and led to a rearrangement of surface features.
“The 0.06 % EDA passivated films also show a smaller root mean square roughness of 13.7 nm than that of the pristine perovskite films,” said the scientists.
They used the film in a perovskite cell a p-i-n structure and tested its performance under standard illumination conditions. The device reportedly achieved a power conversion efficiency of 20.1%, an open-circuit voltage of 1.1 mV, a short-circuit current of 24.0 mA/cm2, and a fill factor of 79.9%. By way comparison, a reference device without the EDA treatment reached an efficiency of 15.9%, an open-circuit voltage of 0.99 V, a short-circuit current of 20.4 mA/cm2, and a fill factor of 73.5%.
“The increase in the open-circuit voltage and the fill factor suggests a suppressed non-radiative recombination and efficient charge extraction in the EDA modified perovskite films,” the researchers said. “The suppression of non-radiative recombination upon EDA passivation is further evidenced through transient photocurrent (TPC) measurements and light intensity dependent (LID) J-V measurements.”
The team determined that the EDA modified cell was able to retain 88% of its initial efficiency after 850 hours, while the reference cell's efficiency fell by 66% within 500 hours.