2D Cations in Tin-Lead Perovskite Solar Cells Increase Conversion Efficiency to 25.5%

Scientists from the US National Renewable Energy Laboratory (NREL) has developed a novel tin-lead perovskite tandem cell fusing different layers of two chemical compounds achieving a power conversion efficiency (PCE) of 25.5%.

The study published in natural energy observations derived from a 2019 experiment that used the cation guanidium thiocyanate (GuaSCN) and achieved 23.1% efficiency in a tin-lead tandem perovskite cell. The GuaSCN cation enhanced the structural and optoelectronic properties of mixed tin-lead (Sn-Pb) perovskite films with a low bandgap of about 1.25 electron-volts.

However, in the new research, the NREL team introduced phenethylammonium iodide (PEAI) as a second compound along with GuaSCN leading to an improved tin-lead perovskite.

NREL researchers Kai Zhu and Jinhui Tong are the authors of the research study with scientists from the University of Colorado-Boulder and the University of Toledo.

Source: Nature

Adding the two compounds revealed that while the best-certified tandem device recorded a voltage of 2.049 volts, NREL’s two-dimensional tandem cell achieved an improved voltage generation of 2.1142 volts, while the lifetime of the cell carriers increased by about 9 microseconds using dimensional engineering mechanics.

The NREL researchers preconditioned their PSCs with continuous illumination under 1 Sun (AM 1.5G, 100 mW/cm2) for 10 seconds. Electron movements are triggered in solar cells when exposed to sunlight, and a long carrier lifetime associated with this movement improves cell efficiency.

The combination of the two additives reduced the defect density associated with tin oxidation to an unprecedented level for tin-lead perovskites.

The team then investigated the external quantum efficiency (EQE) of the PSC device and implemented EQE curves to improve performance.

Perovskite tandem solar cells improve efficiency

Source: Nature

As a result, the integrated Jsc curve of EQE matched the Jsc determined from the JV measurement, channeling the performance with stable solar cell efficiency.

NREL lead scientist and research author Kai Zhu said, “Our experiment represents an accelerated laboratory aging test. At this level of tandem efficiency, the best reported stability in the literature is normally several hundred hours. However, the new perovskite cell retained 80% of its peak efficiency after continuous operation for 1,500 hours under the sun or more than 62 days.

In a recent experiment, materials scientists penetrated the mixed cation of GuaBr (guanidinium bromide) and OABr (n-octylammonium bromide) into the mass of perovskite. They passived the interface between the perovskite absorber and the charge transport layers. The dual cation passivation layer gave an increased efficiency of 23.13%, which was previously 21.37% with a single spacer cation.

Another group of scientists from the University of Rome Tor Vergata reduced cell-module losses in perovskite solar modules and fabricated a 20*20 cm mini panel using the laser ablation method to cancel electrical losses by limiting the current flow in the PSCs. The scientists achieved a PCE of 11.9%.

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