Researchers in China have developed a new type of perovskite solar cells that offer higher efficiency. Developed by scientists from Huaqiao University, these perovskite solar cells offer 26.39% efficiency.
Researchers also revealed that these cells utilize a hole-selective interlayer inhibiting ion diffusion to increase the device’s stability. The major cause of instability of perovskite solar cells is believed to be ion migration.
They claimed that perovskite solar cells have demonstrated limited operational lifetimes, primarily due to the layer-to-layer ion diffusion in the perovskite/doped hole-transport layer (HTL) heterojunction, leading to conductivity drop in HTL and component loss in the perovskite.
Ultra-thin polymeric interlayer
Scientists introduced an ultra-thin (~7 nm) p-type polymeric interlayer (D18) with excellent ion-blocking ability between perovskite and HTL to address these issues.
Published in the journal Nature, the study reveals that the ultra-thin D18 interlayer effectively inhibits the layer-to-layer diffusion of lithium, methylammonium, formamidium, and iodide ions. Additionally, D18 improves the energy-level alignment at the perovskite/HTL interface and facilitates efficient hole extraction.
Researchers also claimed that the resulting perovskite solar cells achieve efficiencies of 26.39%(certified 26.17) and 25.02% with aperture areas of 0.12 and 1.00 square centimeters, respectively. Remarkably, the devices retain 95.4% of the initial efficiency after 1100 hours of operation in maximum power point tracking, representing significant stability advancements for high-efficiency PSCs, according to the study.
Incorporating a hole-selective interlayer in PSCs
Scientists revealed that the idea of incorporating a hole-selective interlayer in PSCs was inspired by proton exchange membrane (PEM) fuel cells, where the PEM serves as a proton conductor while blocking the diffusion of other chemical species. “To achieve highly stable n-i-p PSCs with high efficiency, the inserted hole-selective interlayer is expected to efficiently transport photo-generated holes and inhibit ion diffusion,” said researchers.
The research team built the hole-selective interlayer with an ultrathin polymeric material known as PDTBT2T-FTBDT (D18), which reportedly offers conformal coverage on the surface of perovskite film due to the high fluidity of its diluted solution. It also features matched energy level alignment with the perovskite absorber and the Spiro-OMeTAD HTL, reported PV Magazine.
To confirm the effectiveness of different polymers at inhibiting ion diffusion, researchers deposited PbBr2 films by spin coating PbBr2 solution (0.4 M) on glass substrates at 2000 r.p.m. for 30 seconds and then annealed at 100 °C for 5 min.
“The polymer layers were deposited by spin coating D18, P3HT, and PTAA solutions (2, 4, 6, 10 mg mL−1) on PbBr2 films at 3000 r.p.m. for 30 s, and then the FAI solution (0.4 M) was spin-coated on PbBr2/D18, PbBr2/P3HT, and PbBr2/PTAA films at 1700 r.p.m. for 30 s and then annealed at 100 °C for 10 min,” said researchers.
The team assessed the interlayer’s effectiveness of inhibiting ion diffusion and found it provides superior performance compared to the most commonly used polymers P3HT and PTAA. The results show that the D18 layer has robust ion-blocking capability under thermal stress. D18 is in close contact with the perovskite grain and grain boundary, providing conformal coverage, according to PV Magazine.
