Scientists have simulated dozens of electron transport layer-free cell structures and identified the optimal design with a transparent Zr:In2O3 front electrode, a CuSCN hole transport layer, and a NAN transparent back electrode. They have also optimized the thickness and tire clearance.
Researchers from India have proposed a novel bifacial electron transport layer (ETL)-free cell structure for flexible devices. They optimized this cell using SCAPS-1D simulation software, selecting the most effective combination of the front transparent electrode (FTE), the hole transport layer (HTL) and the rear transparent electrode (RTE). The new structure has achieved an energy conversion efficiency (PCE) of more than 27%.
“ETL-free perovskite solar cells (PSCs) are the most promising and acceptable devices for developing flexible PSCs due to processing at lower temperatures, simplest configuration, and elimination of complex preparation routes, which reduces energy and time,” the researchers said. “They can be easily processed via the roll-to-roll method, spray coating, inkjet printing and can be encapsulated with low-cost flexible layers.”
The scientists started with a reference structure consisting of an FTE layer of PFTO; interfacial defect layer (IDL)1; a perovskite layer (FA0.75MA0.25PbI2.5Br0.5); IDL2; HTL layer of Spiro-OMeTAD; IDL3; and an RTE layer of Cu/Cu2O (PFTO/IDL1/FA0.75MA0.25PbI2.5Br0.5/IDL2/Spiro-OMeTAD/IDL3/Cu/Cu2O). They set the thickness of the perovskite layer to 600 nm.
“While selecting an appropriate FTE, we found that the lower value of conduction band offset (CBO) at the FTE/perovskite interface exhibits improved device performance due to the potential-good-like structure,” the group explains. “CuI and CuSCN exhibit superior band alignment with the perovskite absorbing layer compared to other HTLs, resulting in improved device performance. The electron affinity of RTE plays a crucial role in the band alignment at the RTE/HTL interface and therefore in the performance of the device.”
After finalizing the champion cell, the group examined its band gap and thickness.
“The PCE of the device increases to an optimized band gap of 1.4 eV, achieving a PCE of 24.65% (front illumination) and 25.48% (back illumination). Beyond this band gap, the PCE begins to decrease,” the results showed. “After optimizing the thickness of the absorber layer (800 nm) with a defect density of 1.0 × 10^14 cm−3, the PCE improves to 26.88% and 27.35%.”
They presented their results in “Performance optimization of ETL-free bifacial perovskite solar cells for flexible devices: a simulation study”, which was recently published in Next energy. The team included researchers from the Indian National Institute of Technology and the Indian Institute of Technology.
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