Indian researchers have replaced Spiro-OMeTAD with copper thiocyanate (CuSCN) as the hole-transporting material in a perovskite solar cell. They say the new precursor can provide the same levels of efficiency while reducing moisture leakage.
In “Dual Inorganic CuSCN for Efficient Hole Removal and Moisture Sealing of MAPbI3 perovskite solar cells” – published recently Materials Progress – the researchers explained that CuSCN has emerged as a stable HTM to replace the Spiro-OMeTAD precursor because the latter leads to moisture penetration into the cell, which in turn weakens the perovskite absorber and degrades the solar cell performance.
“With good transparency in the visible and near-infrared regions, appropriate band positions for CuSCN-based devices show comparable efficiency,” they said. “Solution-based processability at low temperatures, cost-effectiveness and repeatability have made industrial profitability possible.”
The scientists built the cell from a fluorine-doped tin oxide (FTO) substrate, electron transport layer containing titanium oxide (TiO2), halide perovskite known as α-formamidinium lead iodide known as α-FAPbI3, CuSCN HTM, and a gold (Au) metal contact.
“MAPbI3 films were deposited by a one-step process,” they said. “The perovskite films were then spin-coated with a hole-transporting material, followed by thermal evaporation of Au at 10 °C.-6 mbar. MAPbI for HTM-free architecture3 the films were coated with gold without HTM coating.”
Academics analyzed the performance of the solar cell and compared it with a reference solar cell with the same configuration and Spiro-OMeTAD HTM. The measurements showed that the CuSCN-based device achieved a power conversion efficiency of 10.1%, compared to 10.0% for the reference cell.
“The CuSCN-based cell retained 70% of its original efficiency due to the robust nature of the CuSCN HTM, which can be seen in devices with a large water contact angle,” they said.
They stated that the cell consists of reducing moisture leakage in the device, which is common in cells using Spiro-OMeTAD.
“The role of the CuSCN-Au interface here is shown to act only as a protective layer for the perovskite film by preventing the ingress of moisture, in contrast to spiro-Au and MAPbI3– Au interfaces that facilitate penetration, they concluded. “This study shows that covering a perovskite with CuSCN HTM acts as a moisture-shielding layer without any changes to the interface or the absorbing layer of the perovskite.”