Researchers from Switzerland's Ecole Polytechnique Fédérale de Lausanne (EPFL), Chinese Academy of Sciences (CAS) and Peking University have developed a perovskite solar cell with a 2D/3D heterojunction architecture.
The cell uses a 2D perovskite layer at the interface between the perovskite and the hole transport layer, which the researchers said can improve charge-carrier transport/extraction while suppressing ion migration. Cells with this architecture usually exhibit large exciton binding energies and are generally more stable than conventional 3D devices due to the protection provided by the organic ligands.
“The interlaminar molecules in 2D perovskites can effectively saturate the 3D perovskite surface to reduce surface defects during the fabrication process, leading to the formation of a potential energy offset for field-effect passivation,” the scientists stated.
The team fabricated the cell with a substrate made of tin oxide (FTO), an electron transport layer made of titanium oxide (TiO2) and tin(IV) oxide (SnO2), a 3D perovskite layer, a 2D perovskite layer, a spiro-OMeTAD hole transport layer, and a metal contact based on gold (Au).
To make the 2D perovskite absorber, the acientists used a precursor called n-butylammonium iodide (BAI), which they said can increase the layer's activation energy to 0.52 eV. “This increase is usually attributed to the larger migration energy owing to the large distance between the interlayer spacings of the 2D perovskite,” they further explained.
Tested under standard illumination conditions, the cell achieved a power conversion efficiency of 25.32%, an open-circuit voltage of 1.159 V, and a fill factor of 83.9%. For comparison, a reference device without the 2D layer achieved an efficiency of 23.02%, an open-circuit voltage of 1.120 V, and a fill factor of 78.9%.
The efficiency value of 25.32% obtained is said to be 'record-breaking for 2D/3D perovskite-based perovskite solar cells'. the device was also able to retain 90% of its initial values after 2000 h of operation.
Using this cell, the scientists also built a mini module that reached an efficiency of 21.39%, an open-circuit voltage of 9.416 V, and a fill factor of 80.3%. The team believes that these modules may potentially achieve an efficiency of around 23% and expect commercial production to be possible in three years, at an estimated cost of $0.02/kWh, and an energy payback time of 6 months.