Natural-born p-doped material for pervoskite solar cells

Researchers in South Korea have found that molybdenum ditelluride could increase carrier generation in perovskite solar cells. They simulated a cell with a perovskite absorber and a layer made of the new material, and determined that its efficiency could exceed 20%.

Image: Sungkyunkwan University, scientific reports, Creative Commons License CC BY 4.0

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Sungkyunkwan University (SKKU) researchers have 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 proposed cell configuration can overcome the present limitations of solar light absorption in perovskite solar cells,” researcher Mohammad Gholipoor told pv magazine. “We think this cell can be another new solution to mitigate this problem.”

The scientists 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 excellently desirable band alignment of MoTe2 with other layers, along with its high near-infrared (NIR) absorption capacity, remarkably paves the way for achieving higher photovoltaic efficiency,” they explained, noting 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%.

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“The calculated results show an appreciable increase in the perovskite solar cell efficiency originating from the short circuit current, compared to the cell without MoTe2,” they said.

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.

They presented the new cell design in “High-performance parallel tandem MoTe2/perovskite solar cell based on reduced graphene oxide as hole transport layer,” which was recently published in Scientific Reports. They 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,” Gholipoor 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.”

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