The efficiency of the indoor perovskite photovoltaic solar cell reaches 32.0%.

Thailand have developed three-cation perovskite solar cells for low-light applications using a manufacturing process based on anti-solvent deposition and vacuum thermal annealing (VTA). "VTA results in a compact, dense, and hard morphology while suppressing trapped States at the surface and grain boundaries, which are responsible for exciton loss,"

they said, emphasizing the importance of the second step for producing high-quality perovskite layers. "Because the indoor light intensity is at least 300 times lower than that of sunlight, it is valuable to induce the formation of dense and uniform perovskite layers by vacuum thermal annealing." The researchers achieved the process

through a vacuum flask connected to a pressure-controlled vacuum pump and located on top of a hot plate to regulate the temperature. They used a perovskite material called FA0.45 MA0.49 Cs0.06Pb (I0.62Br0.32 Cl0.06) 3 with a band gap of 1.80 eV after treatment with bromine and chlorine.

They built a cell with a substrate made of fluorine-doped tin dioxide (FTO), an electron transport layer (ETL) based on tin (group IV) oxide (SnO2), a perovskite absorber, a hole transport layer (HTL) made of Spiro-OMeTAD, a carbon top electrode and another FTO layer. Its effective area is 0.04 cm2. The solar cell showed an energy conversion efficiency of 27.7%, an open circuit voltage of 0.93 V, a short circuit current of 0.16 mA/cm2, and a peak efficiency of 32.0% when tested under indoor light of

1000 Lux. The reference device without VTA treatment has an efficiency of 25.5%, an open-circuit voltage of 0.91 V, a short-circuit current of 0.16 mA/cm2, and a peak efficiency of 30.7%. "VTA results in reduced surface roughness, as well as electron trapping at the bulk and surface,"

the panel said of the superior performance of VTA-based cells. "VTA opens the door to robust perovskite structure formation and can be practically adapted to a variety of perovskite cell compositions for optoelectronic applications ideal for modern society." They described the cell in "Robust Perovskite Layer Formation by Vacuum Thermal Annealing for Indoor Perovskite Solar Cells" published in Scientific Reports.