Defect‐Engineering‐Enabled High‐Efficiency All‐Inorganic Perovskite Solar Cells

The emergence of cesium lead iodide (CsPbI₃) perovskite solar cells (PSCs) has generated enormous interest in the photovoltaic research community. However, in general they exhibit low power conversion efficiencies (PCEs) because of the existence of defects. A new all‐inorganic perovskite material, CsPbI₃:Br:InI₃, is prepared by defect engineering of CsPbI₃. This new perovskite retains the same bandgap as CsPbI₃, while the intrinsic defect concentration is largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere and thus a glovebox is not required. By completely eliminating the labile and expensive components in traditional PSCs, the all‐inorganic PSCs based on CsPbI₃:Br:InI₃ and carbon electrode exhibit PCE and open‐circuit voltage as high as 12.04% and 1.20 V, respectively. More importantly, they demonstrate excellent stability in air for more than two months, while those based on CsPbI₃ can survive only a few days in air. The progress reported represents a major leap for all‐inorganic PSCs and paves the way for their further exploration in order to achieve higher performance.     

Hybrid PbS Quantum‐Dot‐in‐Perovskite for High‐Efficiency Perovskite Solar Cell

In this study, a facile and effective approach to synthesize high‐quality perovskite‐quantum dots (QDs) hybrid film is demonstrated, which dramatically improves the photovoltaic performance of a perovskite solar cell (PSC). Adding PbS QDs into CH₃NH₃PbI₃ (MAPbI₃) precursor to form a QD‐in‐perovskite structure is found to be beneficial for the crystallization of perovskite, revealed by enlarged grain size, reduced fragmentized grains, enhanced characteristic peak intensity, and large percentage of (220) plane in X‐ray diffraction patterns. The hybrid film also shows higher carrier mobility, as evidenced by Hall Effect measurement. By taking all these advantages, the PSC based on MAPbI₃‐PbS hybrid film leads to an improvement in power conversion efficiency by 14% compared to that based on pure perovskite, primarily ascribed to higher current density and fill factor (FF). Ultimately, an efficiency reaching up to 18.6% and a FF of over ≈0.77 are achieved based on the PSC with hybrid film. Such a simple hybridizing technique opens up a promising method to improve the performance of PSCs, and has strong potential to be applied to prepare other hybrid composite materials.     

Amide‐Catalyzed Phase‐Selective Crystallization Reduces Defect Density in Wide‐Bandgap Perovskites

Wide‐bandgap (WBG) formamidinium–cesium (FA‐Cs) lead iodide–bromide mixed perovskites are promising materials for front cells well‐matched with crystalline silicon to form tandem solar cells. They offer avenues to augment the performance of widely deployed commercial solar cells. However, phase instability, high open‐circuit voltage (V_oc) deficit, and large hysteresis limit this otherwise promising technology. Here, by controlling the crystallization of FA‐Cs WBG perovskite with the aid of a formamide cosolvent, light‐induced phase segregation and hysteresis in perovskite solar cells are suppressed. The highly polar solvent additive formamide induces direct formation of the black perovskite phase, bypassing the yellow phases, thereby reducing the density of defects in films. As a result, the optimized WBG perovskite solar cells (PSCs) (E_g ≈ 1.75 eV) exhibit a high V_oc of 1.23 V, reduced hysteresis, and a power conversion efficiency (PCE) of 17.8%. A PCE of 15.2% on 1.1 cm² solar cells, the highest among the reported efficiencies for large‐area PSCs having this bandgap is also demonstrated. These perovskites show excellent phase stability and thermal stability, as well as long‐term air stability. They maintain ≈95% of their initial PCE after 1300 h of storage in dry air without encapsulation.     

High Temperature‐Stable Perovskite Solar Cell Based on Low‐Cost Carbon Nanotube Hole Contact

Mixed ion perovskite solar cells (PSC) are manufactured with a metal‐free hole contact based on press‐transferred single‐walled carbon nanotube (SWCNT) film infiltrated with 2,2,7,‐7‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,90‐spirobifluorene (Spiro‐OMeTAD). By means of maximum power point tracking, their stabilities are compared with those of standard PSCs employing spin‐coated Spiro‐OMeTAD and a thermally evaporated Au back contact, under full 1 sun illumination, at 60 °C, and in a N₂ atmosphere. During the 140 h experiment, the solar cells with the Au electrode experience a dramatic, irreversible efficiency loss, rendering them effectively nonoperational, whereas the SWCNT‐contacted devices show only a small linear efficiency loss with an extrapolated lifetime of 580 h.     

Low‐Temperature Soft‐Cover Deposition of Uniform Large‐Scale Perovskite Films for High‐Performance Solar Cells

Large‐scale high‐quality perovskite thin films are crucial to produce high‐performance perovskite solar cells. However, for perovskite films fabricated by solvent‐rich processes, film uniformity can be prevented by convection during thermal evaporation of the solvent. Here, a scalable low‐temperature soft‐cover deposition (LT‐SCD) method is presented, where the thermal convection‐induced defects in perovskite films are eliminated through a strategy of surface tension relaxation. Compact, homogeneous, and convection‐induced‐defects‐free perovskite films are obtained on an area of 12 cm², which enables a power conversion efficiency (PCE) of 15.5% on a solar cell with an area of 5 cm². This is the highest efficiency at this large cell area. A PCE of 15.3% is also obtained on a flexible perovskite solar cell deposited on the polyethylene terephthalate substrate owing to the advantage of presented low‐temperature processing. Hence, the present LT‐SCD technology provides a new non‐spin‐coating route to the deposition of large‐area uniform perovskite films for both rigid and flexible perovskite devices.     

A Strategy to Produce High Efficiency,High Stability Perovskite Solar Cells Using Functionalized Ionic Liquid‐Dopants

Functionalized imidazolium iodide salts (ionic liquids) modified with ? CH₂? CH?CH₂, ? CH₂C?CH, or ? CH₂C?N groups are applied as dopants in the synthesis of CH₃NH₃PbI₃‐type perovskites together with a fumigation step. Notably, a solar cell device prepared from the perovskite film doped with the salt containing the ? CH₂? CH?CH₂ side‐chain has a power conversion efficiency of 19.21%, which is the highest efficiency reported for perovskite solar cells involving a fumigation step. However, doping with the imidazolium salts with the ? CH₂C?CH and ? CH₂C?N groups result in perovskite layers that lead to solar cell devices with similar or lower power conversion efficiencies than the dopant‐free cell.     

Assembling Mesoscale‐Structured Organic Interfaces in Perovskite Photovoltaics

Mesoscale‐structured materials offer broad opportunities in extremely diverse applications owing to their high surface areas, tunable surface energy, and large pore volume. These benefits may improve the performance of materials in terms of carrier density, charge transport, and stability. Although metal oxides–based mesoscale‐structured materials, such as TiO₂, predominantly hold the record efficiency in perovskite solar cells, high temperatures (above 400 °C) and limited materials choices still challenge the community. A novel route to fabricate organic‐based mesoscale‐structured interfaces (OMI) for perovskite solar cells using a low‐temperature and green solvent–based process is presented here. The efficient infiltration of organic porous structures based on crystalline nanoparticles allows engineering efficient “n‐i‐p” and “p‐i‐n” perovskite solar cells with enhanced thermal stability, good performance, and excellent lateral homogeneity. The results show that this method is universal for multiple organic electronic materials, which opens the door to transform a wide variety of organic‐based semiconductors into scalable n‐ or p‐type porous interfaces for diverse advanced applications.