Chen Weijie

Publication date: Available online 7 May 2018
Source:Joule
Author(s): Jianbo Li, Rahim Munir, Yuanyuan Fan, Tianqi Niu, Yucheng Liu, Yufei Zhong, Zhou Yang, Yuansi Tian, Bo Liu, Jie Sun, Detlef-M. Smilgies, Sigurdur Thoroddsen, Aram Amassian, Kui Zhao, Shengzhong (Frank) Liu
Here, we have identified that the key issue for rational transitioning from spin-coating to blade-coating processes of perovskite films arises from whether intermediate phases participate in the phase transition. In situ characterizations were carried out to provide a comprehensive picture of structural evolution and crystal growth mechanisms. These findings present opportunities for designing an effective process for blade-coating perovskite film: a large-grained dense perovskite film with high crystal quality and photophysical properties can be obtained only via direct crystallization for both spin-coating and blade-coating processes. As a result, the blade-coated MAPbI3 films deliver excellent charge-collection efficiency at both short circuit and open circuit, and photovoltaic properties with efficiencies of 18.74% (0.09 cm²) and 17.06% (1 cm²) in planar solar cells. The significant advances in understanding how the phase transition links spin-coating and blade-coating processes should provide a path toward high-performance printed perovskite devices.

Graphical abstract

Teaser

Hybrid organic-inorganic perovskite solar cells have recently emerged as a highly promising and inexpensive solution for sustainable energy. However, a full comprehensive picture of the phase transition including structural evolution and crystal growth mechanisms is missing for both scalable printing and lab-based spin-coating processes. Here we reveal fundamental insights into the perovskite phase transition when moving between spin-coating and printing processes, providing a rational path toward optimization of printed devices.

Publication date: Available online 7 May 2018
Source:Joule
Author(s): Hui Bian, Dongliang Bai, Zhiwen Jin, Kang Wang, Lei Liang, Haoran Wang, Jingru Zhang, Qian Wang, Shengzhong (Frank) Liu
All-inorganic perovskite shows great potential for photovoltaic applications due to its excellent solar cell performance and atmospheric stability. Here, a CsPbI2+x Br1−x perovskite solar cell with a graded bandgap is explored using CsPbBrI2 and CsPbI3 quantum dots as component cells. Four strategies were pursued to boost the device performance. First, CsPbI2Br film was fabricated as the main absorber, with the component cell showing remarkable power conversion efficiency (PCE) as high as 13.45%. Second, by Mn²⁺ substitution, SCN⁻ capping, and [(NH2)2CH]⁺ treatment, stable and high-mobility CsPbI3 quantum dot (QD) film was attained. Third, a halide-ion-profiled heterojunction was designed at the CsPbBrI2/CsPbI3 QD interface to achieve proper band-edge bending as graded bandgap for improved carrier collection. Finally, the CsPbI3 QD layer was optimized in the graded bandgap structure to achieve maximum overall light harvesting. As a result, the device achieved a PCE of 14.45%. This is the highest efficiency ever reported for inorganic perovskite solar cells.

Graphical abstract

Teaser

Here, a high-performance graded bandgap structure-based solar cell was designed and demonstrated, comprising a CsPbI2Br bottom cell and a CsPbI3 QD top cell. Several optimizations were conducted to boost the device performance. As a result, the extended photoresponse, high carrier mobility, and well-matched energy levels afford a record power conversion efficiency of 14.45%, coupled with a high J SC of 15.25 mA/cm². The result shows that optical and energy-band manipulation is an effective approach for improving the performance of inorganic perovskite solar cells.

Advanced Energy Materials, Volume 8, Issue 13, May 4, 2018.

The ability to control the response of metamaterial structures can facilitate the development of new terahertz devices, with applications in spectroscopy and communications. We demonstrate ultrafast frequency-agile terahertz metamaterial devices that enable such a capability, in which multiple perovskites can be patterned in each unit cell with micrometer-scale precision. To accomplish this, we developed a fabrication technique that shields already deposited perovskites from organic solvents, allowing for multiple perovskites to be patterned in close proximity. By doing so, we demonstrate tuning of the terahertz resonant response that is based not only on the optical pump fluence but also on the optical wavelength. Because polycrystalline perovskites have subnanosecond photocarrier recombination lifetimes, switching between resonances can occur on an ultrafast time scale. The use of multiple perovskites allows for new functionalities that are not possible using a single semiconducting material. For example, by patterning one perovskite in the gaps of split-ring resonators and bringing a uniform thin film of a second perovskite in close proximity, we demonstrate tuning of the resonant response using one optical wavelength and suppression of the resonance using a different optical wavelength. This general approach offers new capabilities for creating tunable terahertz devices.

Author Correction: III–V-on-silicon solar cells reaching 33% photoconversion efficiency in two-terminal configuration

Author Correction: III–V-on-silicon solar cells reaching 33% photoconversion efficiency in two-terminal configuration, Published online: 03 May 2018; doi:10.1038/s41560-018-0165-5

Author Correction: III–V-on-silicon solar cells reaching 33% photoconversion efficiency in two-terminal configuration

Advanced Functional Materials, Volume 28, Issue 18, May 4, 2018.

Advanced Energy Materials, EarlyView.

Advanced Materials, EarlyView.

Hybrid perovskite films approaching the radiative limit with over 90% photoluminescence quantum efficiency

Hybrid perovskite films approaching the radiative limit with over 90% photoluminescence quantum efficiency, Published online: 30 April 2018; doi:10.1038/s41566-018-0154-z

Surface treatment is shown to yield passivated perovskite films with very high quasi-Fermi level splitting and internal photoluminescence quantum efficiency, indicating that further improvements in the performance of perovskite optoelectronics should be feasible.

Advanced Energy Materials, Volume 8, Issue 12, April 25, 2018.

Advanced Energy Materials, Volume 8, Issue 12, April 25, 2018.

Advanced Energy Materials, EarlyView.

Advanced Materials, EarlyView.

The interplay between the electronic and lattice degrees of freedom in nonequilibrium states of strongly correlated systems has been debated for decades. Although progress has been made in establishing a hierarchy of electronic interactions with the use of time-resolved techniques, the role of the phonons often remains in dispute, a situation highlighting the need for tools that directly probe the lattice. We present the first combined megaelectron volt ultrafast electron diffraction and time- and angle-resolved photoemission spectroscopy study of optimally doped Bi₂Sr₂CaCu₂O₈₊. Quantitative analysis of the lattice and electron subsystems’ dynamics provides a unified picture of nonequilibrium electron-phonon interactions in the cuprates beyond the N-temperature model. The work provides new insights on the specific phonon branches involved in the nonequilibrium heat dissipation from the high-energy Cu–O bond stretching "hot" phonons to the lowest-energy acoustic phonons with correlated atomic motion along the <110> crystal directions and their characteristic time scales. It reveals a highly nonthermal phonon population during the first several picoseconds after the photoexcitation. The approach, taking advantage of the distinct nature of electrons and photons as probes, is applicable for studying energy relaxation in other strongly correlated electron systems.