Zhibin Yang

Stable Low-Bandgap Pb–Sn Binary Perovskites for Tandem Solar Cells

A low-bandgap (1.33 eV) Sn-based MA0.5 FA0.5 Pb0.75 Sn0.25 I3 perovskite is developed via combined compositional, process, and interfacial engineering. It can deliver a high power conversion efficiency (PCE) of 14.19%. Finally, a four-terminal all-perovskite tandem solar cell is demonstrated by combining this low-bandgap cell with a semitransparent MAPbI3 cell to achieve a high efficiency of 19.08%.

Highly Efficient Perovskite–Perovskite Tandem Solar Cells Reaching 80% of the Theoretical Limit in Photovoltage

Organic-inorganic hybrid perovskite multijunction solar cells have immense potential to realize power conversion efficiencies (PCEs) beyond the Shockley-Queisser limit of single-junction solar cells; however, they are limited by large nonideal photovoltage loss (V oc,loss ) in small- and large-bandgap subcells. Here, an integrated approach is utilized to improve the V oc of subcells with optimized bandgaps and fabricate perovskite-perovskite tandem solar cells with small V oc,loss . A fullerene variant, Indene-C60 bis-adduct, is used to achieve optimized interfacial contact in a small-bandgap (≈1.2 eV) subcell, which facilitates higher quasi-Fermi level splitting, reduces nonradiative recombination, alleviates hysteresis instabilities, and improves V oc to 0.84 V. Compositional engineering of large-bandgap (≈1.8 eV) perovskite is employed to realize a subcell with a transparent top electrode and photostabilized V oc of 1.22 V. The resultant monolithic perovskite-perovskite tandem solar cell shows a high V oc of 1.98 V (approaching 80% of the theoretical limit) and a stabilized PCE of 18.5%. The significantly minimized nonideal V oc,loss is better than state-of-the-art silicon-perovskite tandem solar cells, which highlights the prospects of using perovskite-perovskite tandems for solar-energy generation. It also unlocks opportunities for solar water splitting using hybrid perovskites with solar-to-hydrogen efficiencies beyond 15%.

Improved efficiency and stability of Pb–Sn binary perovskite solar cells by Cs substitution

Partially replacing Pb with Sn in organic–inorganic lead halide perovskites has been proven as a promising approach to reduce environmental toxicity and develop low bandgap (as low as 1.20 eV) perovskite solar cells (PVSCs) beneficial for constructing perovskite-based tandem solar cells. In this work, we demonstrated that partially replacing MA+ or FA+ with Cs+ in a Pb–Sn binary perovskite system can effectively retard the associated crystallization rate to facilitate homogenous film formation, subsequently resulting in enhanced device performance and stability, especially for high Sn-containing compositions. The representative MA0.9Cs0.1Pb0.5Sn0.5I3 PVSC with a low Eg of 1.28 eV not only achieves an improved efficiency up to 10.07% but also possesses much improved thermal and ambient stability as compared to the pristine MAPb0.5Sn0.5I3 PVSC showing poorer efficiency (6.36%) and stability. Similarly, when Cs was introduced into FAPb1−xSnxI3 perovskite, enhanced performance was observed, affirming its general applicability and beneficial role in mediating the crystal growth and film formation of Pb–Sn binary perovskites.

Large Grained Perovskite Solar Cells Derived from Single-Crystal Perovskite Powders with Enhanced Ambient Stability

In this study, we demonstrate the large grained perovskite solar cells prepared from precursor solution comprising single-crystal perovskite powders for the first time. The resultant large grained perovskite thin film possesses a negligible physical (structural) gap between each large grain and is highly crystalline as evidenced by its fan-shaped birefringence observed under polarized light, which is very different from the thin film prepared from the typical precursor route (MAI + PbI2).

Ideal Bandgap Organic–Inorganic Hybrid Perovskite Solar Cells

Extremely high power conversion efficiencies (PCEs) of ≈20-22% are realized through intensive research and development of 1.5-1.6 eV bandgap perovskite absorbers. However, development of ideal bandgap (1.3-1.4 eV) absorbers is pivotal to further improve PCE of single junction perovskite solar cells (PVSCs) because of a better balance between absorption loss of sub-bandgap photons and thermalization loss of above-bandgap photons as demonstrated by the Shockley-Queisser detailed balanced calculation. Ideal bandgap PVSCs are currently hindered by the poor optoelectronic quality of perovskite absorbers and their PCEs have stagnated at <15%. In this work, through systematic photoluminescence and photovoltaic analysis, a new ideal bandgap (1.35 eV) absorber composition (MAPb0.5 Sn0.5 (I0.8 Br0.2 )3 ) is rationally designed and developed, which possesses lower nonradiative recombination states, band edge disorder, and Urbach energy coupled with a higher absorption coefficient, which yields a reduced Voc,loss (0.45 V) and improved PCE (as high as 17.63%) for the derived PVSCs. This work provides a promising platform for unleashing the complete potential of ideal bandgap PVSCs and prospects for further improvement.

Solution-processed chalcopyrite–perovskite tandem solar cells in bandgap-matched two- and four-terminal architectures

Solution-processed chalcopyrite and perovskite devices of various bandgaps are combined in four- and two-terminal mechanically-stacked tandem architectures. The excellent low-light performance of Cu(In,Ga)(S,Se)2 and low-bandgap CuIn(S,Se)2 cells and the high efficiency of novel NIR-transparent inverted perovskite cells with C60/bis-C60/ITO as electron transport layers, enabled stabilized two- and four-terminal tandem efficiencies up to 18.5% and 18.8%, respectively, which represent a new record for tandem devices with solution-processed chalcopyrite and perovskite absorbers.