Abnormal spatial heterogeneity governing the charge-carrier mechanism in efficient Ruddlesden-Popper perovskite solar cells

Layered Ruddlesden-Popper perovskite (RPP) photovoltaics have gained substantial attention owing to their excellent air stability. However, their photovoltaic performance is still limited by the unclear real-time charge-carrier mechanism of operating devices. Herein, we report the correlation between the charge-carrier mechanism and the spatially heterogeneous RPP bulks induced by distinct sublattice cations in the state-of-the-art antisolvent-driven RPP devices. In particular, abnormal heterogeneities ranging from the lateral long-range to local sub-grain scale and corresponding charge-carrier behaviours are visualized for triple-cation RPPs. We discovered that such heterogeneities with a unitary 2D/3D hybrid suppress lattice vibrations and reduce Frohlich interactions by about 2 times, significantly promoting charge-carrier dynamics. Consequently, optimized triple-cation RPP solar cells greatly outperform their mono-cation counterparts. Furthermore, this principle can be applicable irrespective of 2D layer thickness (n > 2) and substrate type. This work provides a rationale for leveraging a disordered structure to stimulate charge-carrier motion and suggests the design principle of low-dimensional perovskites.

Hot Gas‐Blowing Assisted Crystallinity Management of Bar‐Coated Perovskite Solar Cells and Modules

The bar‐coating technique for perovskite solar cells has been studied as a scalable process in relation to solar cell commercialization. In large‐area bar coating, solvents with the high boiling points like dimethylformamide or γ‐butyrolactone have difficulty in obtaining uniform and planar film at room temperature as they have slow evaporation rate. As an alternative, 2‐methoxyethanol is a volatile and polar solvent, which is useful on a bar coating if applied using an air‐blowing method with an air knife. Herein, a hot gas‐blowing method for the fabrication of a perovskite layer to achieve both proper solvent evaporation and high crystallinity is developed. With 75 °C of N2 blowing on the bar‐coated perovskite solution, highly crystalline perovskite films with large grains without voids are fabricated, showing excellent optical and electrical characteristics, such as long carrier lifetime, few carrier recombinations, and low trap density. Both small‐area solar cells and large‐area modules show good performance, 20.85% for the solar cell and 15.4% for the solar module. The results indicate that the newly proposed method can equally be applied to the fabrication of large‐area solar cells toward commercialization

Rational Core–Shell Design of Open Air Low Temperature In Situ Processable CsPbI 3

As a promising alternative, inorganic perovskite nanocrystals allow reinforced stability of photovoltaic device. Unfortunately, directly assembling these nanocrystals into film is uncontrollable. Instead, in situ assembling technology under low temperature in open air is attractive but limited due to the tendency of nonperovskite transition. The adverse shell ligands and unstable core lattices are known as the fundamental problems. In order to address this issue, here proposed is a rational core-shell design: 1) with respect to ligands, a new one, 4-fluorophenethylammonium iodide, is used to enhance bonding force and charge coupling between ligands and nanocrystals; 2) with respect to lattices, a novel compound H2PbI4 is employed to assist divalent ion (Mn2+) doping into perovskite lattices. By low temperature in situ processing CsPbI3 quasi-nanocrystal film, the highest power conversion efficiency of 13.4% for p-i-n solar cells is achieved, which retains 92% after 500 h in ambient air. The current study underlines the significance of rational hierarchical design of inorganic perovskite nanocrystals, especially for low temperature in situ processable electronic devices.N

R4N+ and Cl??? stabilized ??-formamidinium lead triiodide and efficient bar-coated mini-modules

The higher thermodynamic stability of formamidinium lead triiodide (FAPbI3) in the yellow non-perovskite (8-phase) than the black perov-skite (a-phase) at room temperature causes spontaneous a-phase to 8-phase transition. Stabilization of a-FAPbI3 by alloying the perovskite composition is limited by band gap broadening and halide segregation. Furthermore, commercial PSCs require coating methods suitable for large-area modules. Herein, we report a-phase stabilization of FAPbI3 without band gap broadening using R4N+ cations and Cl- anions. Subsequently, high-efficiency perovskite so-lar mini-modules (PSMs) were fabricated using a bar-coating process with simultaneous defect passivation and hole-transport promotion which exhibited a maximum power conversion efficiency (PCE) of 21.23% (certified 20.33%, 36.4-cm2 area). The PCE in the 1-cm2 area fabricated by bar-coating was 23.24% (certified 22.79%, the highest in those fabricated by scalable bar-coating method). Furthermore, the encapsulated PSM retained 93% of its initial PCE, even after 870 h under continuous one-sun illumination

Structural Isomer of Fluorinated Ruddlesden-Popper Perovskites Toward Efficient and Stable 2D/3D Perovskite Solar Cells

International audienceDefect passivation using two-dimensional (2D)-layered perovskites with organic spacers on 3D bulk perovskites has been proposed as an effective strategy to improve perovskite solar cell stability and efficiency. Specifically, fluorination of the organic spacers has been employed due to the resulting hydrophobic nature and the defect passivation characteristics. In addition to the type of functional groups attached to the spacer molecules, conformational changes of fluorine isomers on layered perovskites can provide an extended strategy to control a variety of opto-electrical properties related to the interlayer spacing. As a model system for the structural isomer of fluorinated spacers, meta-CF3 and para-CF3 groups anchored to phenethylammonium iodide (PEAI) spacer molecules are employed to synthesize 2D perovskites and to investigate their full potential as an interfacial modifier for perovskite solar cells. The fluorination position change leads to altered opto-electrical characteristics in layered perovskites. Although they possess identical functional groups, the different orientations of the functional groups used in the perovskite layer deposited on the 3D perovskite absorber result in distinct electrical properties of 2D/3D heterostructures due to dissimilar intermolecular interactions. The 2D perovskite with meta-CF3-PEAI spacers exhibits an enhancement of the charge transport in the out-of-plane orientation and an improved suppression of the trap states of 3D perovskites while also providing a more favorable energy alignment for efficient charge transfers. Theoretical simulations are consistent with the experimental results. The structural isomers of fluorination anchoring to spacer cations alter the structural configuration of the spacer as well as the interlayer spacing that can improve the performance and the stability of 2D/3D perovskite solar cells

High‐Performance Solution‐Processed Double‐Walled Carbon Nanotube Transparent Electrode for Perovskite Solar Cells

Double-walled carbon nanotubes are between single-walled carbon nanotubes and multiwalled carbon nanotubes. They are comparable to single-walled carbon nanotubes with respect to the light optical density, but their mechanical stability and solubility are higher. Exploiting such advantages, solution-processed transparent electrodes are demonstrated using double-walled carbon nanotubes and their application to perovskite solar cells is also demonstrated. Perovskite solar cells which harvest clean solar power have attracted a lot of attention as a next-generation renewable energy source. However, their eco-friendliness, cost, and flexibility are limited by the use of transparent oxide conductors, which are inflexible, difficult to fabricate, and made up of expensive rare metals. Solution-processed double-walled carbon nanotubes can replace conventional transparent electrodes to resolve such issues. Perovskite solar cells using the double-walled carbon nanotube transparent electrodes produce an operating power conversion efficiency of 17.2% without hysteresis. As the first solution-processed electrode-based perovskite solar cells, this work will pave the pathway to the large-size, low-cost, and eco-friendly solar devices.N

Foldable Perovskite Solar Cells Using Carbon Nanotube-Embedded Ultrathin Polyimide Conductor

Recently, foldable electronics technology has become the focus of both academic and industrial research. The foldable device technology is distinct from flexible technology, as foldable devices have to withstand severe mechanical stresses such as those caused by an extremely small bending radius of 0.5 mm. To realize foldable devices, transparent conductors must exhibit outstanding mechanical resilience, for which they must be micrometer-thin, and the conducting material must be embedded into a substrate. Here, single-walled carbon nanotubes (CNTs)–polyimide (PI) composite film with a thickness of 7 µm is synthesized and used as a foldable transparent conductor in perovskite solar cells (PSCs). During the high-temperature curing of the CNTs-embedded PI conductor, the CNTs are stably and strongly p-doped using MoOx, resulting in enhanced conductivity and hole transportability. The ultrathin foldable transparent conductor exhibits a sheet resistance of 82 Ω sq.−1 and transmittance of 80% at 700 nm, with a maximum-power-point-tracking-output of 15.2% when made into a foldable solar cell. The foldable solar cells can withstand more than 10 000 folding cycles with a folding radius of 0.5 mm. Such mechanically resilient PSCs are unprecedented; further, they exhibit the best performance among the carbon-nanotube-transparent-electrode-based flexible solar cells.Peer reviewe