All-perovskite–based polycrystalline thin-film tandem solar cells have the potential to deliver efficiencies of >30%. However, the performance of all-perovskite–based tandem devices has been limited by the lack of high-efficiency, low–band gap tin-lead (Sn-Pb) mixed-perovskite solar cells (PSCs). We found that the addition of guanidinium thiocyanate (GuaSCN) resulted in marked improvements in the structural and optoelectronic properties of Sn-Pb mixed, low–band gap (~1.25 electron volt) perovskite films. The films have defect densities that are lower by a factor of 10, leading to carrier lifetimes of greater than 1 microsecond and diffusion lengths of 2.5 micrometers. These improved properties enable our demonstration of >20% efficient low–band gap PSCs. When combined with wider–band gap PSCs, we achieve 25% efficient four-terminal and 23.1% efficient two-terminal all-perovskite–based polycrystalline thin-film tandem solar cells.
Recent achievements of 2D perovskites for various optoelectronic applications along with their basic properties and future opportunities are discussed.
Maximizing the power conversion efficiency (PCE) of perovskite/silicon tandem solar cells that can exceed the Shockley-Queisser single-cell limit requires a high-performing, stable perovskite top cell with a wide bandgap. We developed a stable perovskite solar cell with a bandgap of ~1.7 electron volts that retained more than 80% of its initial PCE of 20.7% after 1000 hours of continuous illumination. Anion engineering of phenethylammonium-based two-dimensional (2D) additives was critical for controlling the structural and electrical properties of the 2D passivation layers based on a lead iodide framework. The high PCE of 26.7% of a monolithic two-terminal wide-bandgap perovskite/silicon tandem solar cell was made possible by the ideal combination of spectral responses of the top and bottom cells.
This work shows a bimolecular additive engineering approach to prepare highly efficient wide-band-gap perovskite solar cells. The coupling of PEA + and SCN À provides a synergistic effect that overcomes growth challenges with either additive individually and improves perovskite quality with enhanced crystallinity, reduced defect density, and improved carrier mobility and lifetime. When coupling a semitransparent wide-band-gap perovskite top cell with a low-band-gap CIGS bottom cell, we achieve a 25.9%-efficient polycrystalline perovskite/CIGS 4-terminal thinfilm tandem solar cell.
The first bottom-up solution-processed perovskite–perovskite tandem solar cell has been successfully fabricated via an optimized charge recombination layer comprising spiro-OMeTAD/PEDOT:PSS/PEI/PCBM:PEI. The as-fabricated tandem device delivers an open voltage of up to 1.89 V, close to the sum of the two perovskite subcells.
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