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Japanese scientists have developed a lead-free tin sulfide solar cell for application in perovskite-silicon tandem photovoltaic devices. Using a new passivation technique based on the use of phenylsilane (PhSiH3) as a reducing agent, they managed to considerably increase the efficiency of the cell compared to a reference device without PhSiH3 treatment.
Researchers at the University of Electrocommunications in Japan have developed a tin perovskite solar cell with a bandgap greater than 1.6 eV that could be used as a top layer in lead-free perovskite-silicon tandem solar cells.
The scientists recognized that the replacement of lead (Pb) by tin (Sn) in perovskite solar cells implies a considerable reduction in power conversion efficiency and explained that this depends on the presence of tin(IV) sulfide ( Sn4+), which is formed by the oxidation of Sn during perovskite ink preparation, perovskite ink maintenance, or perovskite film baking.
To reduce the presence of concentrated Sn4+ on the surface of the perovskite film, the research group adopted a new passivation strategy based on the use of phenylsilane (PhSiH3) as a reducing agent.
“To our knowledge, there is no report on the passivation of surfaces with organic solutions composed of reducing agents,” he explained, noting that the use of PhSiH3 results in the formation of a siloxane layer, which creates better contact between the absorbent hydrophilic tin perovskite and the hydrophobic buckminsterfullerene (C60) used for the electron transport layer (ETL). “After surface passivation, the contact angle increased, showing that the perovskite surface became more hydrophobic.”
The academics built the cell with a glass substrate and a fluorine-doped tin oxide (FTO), a hole transport layer (HTL) made with PEDOT:PSS, a polymer known for its low-cost properties and easy preparation, an absorber made of a lead-free perovskite material known as ASnI2Br, a C60-based ETL, a bathocuproin (BCP) buffer layer, and a silver (Ag) metal contact.
The scientists compared the performance of the solar cell with that of a reference device that had not been subjected to the novel passivation treatment. They found that the latter reached an efficiency of 3.65%, while the treated device reached 5.50%, which, according to them, demonstrates the effectiveness of the treatment with PhSiH3.
The results are explained by a faster decay of photoluminescence after surface treatment, a lower series resistance and a greater resistance to charge recombination after surface treatment, they noted. “PhSiH3 was shown to be effective in reducing the Sn4+ accumulated in the perovskite films and in achieving better contact of the perovskite layer with the C60 layer,” they concluded.
The solar cell design and passivation techniques are described in the article “ Efficiency-enhancement of lead-free ASnI2Br perovskite solar cells by phenyltrihydrosilane passivation effective for Sn4+ reduction and hydrophobization ” lead-free by passivation with phenyltrihydrosilane effective for the reduction and hydrophobization of Sn4+), published in Next Materials . |
