Researchers from South Korea's Sungkyunkwan University (SKKU) have found that molybdenum ditelluride could increase carrier generation in perovskite solar cells.
They simulated a tandem solar cell with two absorbers based on methylammonium lead triiodide (CH3NH3PbI3) – a perovskite with high photoluminescence quantum yield – and molybdenum ditelluride (MoTe2), which is known for being naturally p-doped, with cascaded bandgaps to absorb a wider solar spectrum. The team determined that its efficiency could exceed 20%.
The team built the cell with an indium tin oxide (ITI) substrate, an electron transport layer (ETL) based on titanium oxide (TiO2), a CH3NH3PbI3 layer, a MoTe2 layer, a spiro-OMeTAD hole-blocking layer, and a silver (Ag) metal contact.
The researchers explained that the desirable band alignment of MoTe2 with other layers, along with its high near-infrared (NIR) absorption capacity, paves the way for achieving higher photovoltaic efficiency. They also noted that the ideal thickness of the MoTe2 absorber should be around 25 nanometers.
They found that the CH3NH3PbI3 and MoTe2 layers contributed to 61% and 39% of carrier generation, respectively. They noted that a cell fabricated with this configuration could reach a power conversion efficiency of 20.32%.
According to the team, the results showed an appreciable increase in the perovskite solar cell efficiency originating from the short circuit current, compared to the cell without MoTe2. However, stacking the absorbers with different bandgaps led to a decline in the open-circuit voltage, due to the hole transport deterioration in the absorbing area.
“In order to alleviate the unavoidable issue, we inserted a graphene oxide layer with a thickness of 1.5 nm. Consequently, we observed that the open circuit voltage increases as much as 0.1 eV,” they said.
The scientists are now trying to get experimental results in line with their simulation results.
“Transition-metal dichalcogenides (TMDs) such as MoTe2 are not too expensive and can be easily prepared through exfoliation method and growing, that is, the cost of a cell here is not an issue,” the team explained. “However, there are some technical and experimental issues that should be addressed, such as the perfect transfer of MoTe2 flakes on rough perovskite layers or high interlayer recombination of two absorbers.”
