Researchers in China, led by Nanjing University, have designed a tandem perovskite-silicon solar cell with a top perovskite device based on an absorber treated with n-butanol (nBA), which reportedly reduces the detrimental effects of moisture in manufacturing processes carried out in air environment. The resulting PV device is said to have improved charge collection.
The nBA used by the team is a clear, colorless alcohol used as a cleaning agent in many industries, including electronics manufacturing. The team explained that it offers low polarity and saturation vapor pressure and ensures that the typical detrimental effects of moisture in perovskite cell fabrication in an ambient environment can be significantly reduced.
The perovskite film used in the tandem cell's top device had an active area of 0.049 cm2 and was fabricated via co-evaporation and blade-coating techniques, which the team said meets the requirements for large-area fabrication of the perovskite films.
“It is worth noting that the second step was implemented in air to match the realistic production environment,” the scientists stated in their recent paper, noting that nBa replaced common ethanol and isopropyl alcohol, which negatively affect film uniformity. “Both the polarity and evaporation rate of the solvent have a joint effect on H2O absorption levels. In this view, nBA emerges as the optimal solvent for our specific requirements.”
The nBa-based film was found to promote improved charge collection, due to the larger grain sizes minimizing recombination, compared to control films developed with conventional solvents.
The researchers designed the top cell with a glass-coated indium tin oxide (ITO) absorber, a nickel (II) oxide (NiO) layer, a hole transport layer (HTL) with a self-assembled monolayer (SAM), a perovskite absorber with an energy bandgap of 1.68 eV, an electron transport layer based on buckminsterfullerene (C60) and a tin oxide (SnOx) buffer layer, and a copper (Cu) electrode. Tested under standard illumination conditions, this device achieved a power conversion efficiency of 20.8%.
The top device was then integrated in a tandem cell with an active area of 1.044 cm2 integrating a bottom heterojunction silicon solar cell. This cell achieved an efficiency of 29.4%, an open-circuit voltage of 1.83 V, a short-circuit current density of 20.45 mA cm−2, and a fill factor of 78.63%.
The team was also able to certify a 28.7% efficiency for the tandem cell and 26.3% for a device with an aperture area of 16 cm2. “The encapsulated device retained 96.8% of the initial output after 780 h of maximum power point tracking,” the researchers added. “Additionally, we have showcased the potential for commercial scaling by achieving a conversion efficiency of 25.9% for 16 cm² devices fabricated via slot-die coating.”
“This solvent engineering strategy demonstrates the feasibility of commercial perovskite-silicon tandem solar cells,” the team stated.
