JIALINGBO

Chlorine‐Substituted Graphdiyne

In article number 1900241, Tonggang Jiu and co‐workers introduce chlorine‐substituted graphdiyne into MAPbI₃‐based perovskite solar cells to produce a peak efficiency of 20.34% with suppressed J‐V hysteresis, which results from the interaction of derivated graphdiyne and PCBM, to be exact, four types of non‐covalent bonds. These findings suggest that derivated graphdiyne could have potential applications in solar cells and other photoelectric devices.

The elastic modulus of 3D perovskite is very close to that of human bones and the elastic modulus of 2D perovskite with long chains is close to that of cartilage. By reconstructing a crystal lattice with different A cations at the surface of perovskite films, a nature “bone‐joint” configuration is built in perovskite, which provides a cushioning effect to external stresses.

Abstract

To improve the photovoltaic performance (both efficiency and stability) in hybrid organic–inorganic halide perovskite solar cells, perovskite lattice distortion is investigated with regards to residual stress (and strain) in the polycrystalline thin films. It is revealed that residual stress is concentrated at the surface of the as‐prepared film, and an efficient method is further developed to release this interfacial stress by A site cation alloying. This results in lattice reconstruction at the surface of polycrystalline thin films, which in turn results in low elastic modulus. Thus, a “bone‐joint” configuration is constructed within the interface between the absorber and the carrier transport layer, which improves device performance substantially. The resultant photovoltaic devices exhibit an efficiency of 21.48% with good humidity stability and improved resistance against thermal cycling.

The elastic modulus of 3D perovskite is very close to that of human bones and the elastic modulus of 2D perovskite with long chains is close to that of cartilage. By reconstructing a crystal lattice with different A cations at the surface of perovskite films, a nature “bone‐joint” configuration is built in perovskite, which provides a cushioning effect to external stresses.

Abstract

To improve the photovoltaic performance (both efficiency and stability) in hybrid organic–inorganic halide perovskite solar cells, perovskite lattice distortion is investigated with regards to residual stress (and strain) in the polycrystalline thin films. It is revealed that residual stress is concentrated at the surface of the as‐prepared film, and an efficient method is further developed to release this interfacial stress by A site cation alloying. This results in lattice reconstruction at the surface of polycrystalline thin films, which in turn results in low elastic modulus. Thus, a “bone‐joint” configuration is constructed within the interface between the absorber and the carrier transport layer, which improves device performance substantially. The resultant photovoltaic devices exhibit an efficiency of 21.48% with good humidity stability and improved resistance against thermal cycling.

Perovskite solar cells still have huge room for improvement in photoelectric conversion efficiency. One of the constraints is the defects at the interface between the perovskite and the transport layer. Passivation is considered a key measure to limit defects. This paper systematically categorizes the effective passivation strategies for perovskites in recent years and gives a future outlook.

Abstract

The disorderly distribution of defects in the perovskite or at the grain boundaries, surfaces, and interfaces, which seriously affect carrier transport through the formation of nonradiative recombination centers, hinders the further improvement on the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Several defect passivation strategies have been confirmed as an efficient approach for promoting the performance of PSCs. Herein, recent progress in the defect passivation toward efficient perovskite solar cells are summarized, and a classification of common passivation strategies that elaborate the mechanism according to the location of the defects and the type of passivation agent is presented. Finally, this review offers likely prospects for future trends in the development of passivation strategies.

Nature Communications, Published online: 09 October 2019; doi:10.1038/s41467-019-12613-8

New natriumion‐functionalized carbon nano‐dots (CNDs@Na) are rationally designed for planar inverted perovskite solar cells as an interface modification layer to reduce interfacial defects. CNDs@Na interfacial modification passivates surface trap states and reduces trap density at the interface, which facilitates photogenerated holes extraction and suppresses charge recombination.

Realizing the full potential of perovskite photovoltaic requires stringent control over nonradiative losses in the devices. Herein, the interfacial carrier recombination of inverted planar perovskite solar cells (PSCs) is suppressed using rationally designed natriumion‐functionalized carbon nano‐dots (CNDs@Na). The binding effect of carbon dots on Na⁺ inhibits the interstitial occupancy of alkali cations and reduces the microstrain of the polycrystalline film. Furthermore, modified surface wettability improves the ordering and crystal size of perovskite, which restrains ion diffusion and improves interfacial contact, leading to reduced interfacial charge recombination. Consequently, the effective interfacial passivation and crystallization control enhance the photovoltaic performance and long‐term stability of PSCs, resulting in an efficiency of over 20% with negligible hysteresis.

The electron extracting properties of the widely used electron transporting layer (ETL) material Phen‐NaDPO are remarkably enhanced via simple addition of the wide‐bandgap inorganic material tin (II) thiocyanate (Sn(SCN)₂). Use of this hybrid ETL system in organic and perovskite solar cells results in consistent efficiency improvements due to the reduced trap‐assisted recombination and efficient electron extraction.

Abstract

A simple approach that enables a consistent enhancement of the electron extracting properties of the widely used small‐molecule Phen‐NaDPO and its application in organic solar cells (OSCs) is reported. It is shown that addition of minute amounts of the inorganic molecule Sn(SCN)₂ into Phen‐NaDPO improves both the electron transport and its film‐forming properties. Use of Phen‐NaDPO:Sn(SCN)₂ blend as the electron transport layer (ETL) in binary PM6:IT‐4F OSCs leads to a remarkable increase in the cells' power conversion efficiency (PCE) from 12.6% (Phen‐NaDPO) to 13.5% (Phen‐NaDPO:Sn(SCN)₂). Combining the hybrid ETL with the best‐in‐class organic ternary PM6:Y6:PC₇₀BM systems results to a similarly remarkable PCE increase from 14.2% (Phen‐NaDPO) to 15.6% (Phen‐NaDPO:Sn(SCN)₂). The consistent PCE enhancement is attributed to reduced trap‐assisted carrier recombination at the bulk‐heterojunction/ETL interface due to the presence of new energy states formed upon chemical interaction of Phen‐NaDPO with Sn(SCN)₂. The versatility of this hybrid ETL is further demonstrated with its application in perovskite solar cells for which an increase in the PCE from 16.6% to 18.2% is also demonstrated.

The polystyrene is introduced into perovskite solar cells as the buffer layer between the SnO₂ and perovskite, which can release the stress during the perovskite annealing. A large lattice, fewer defect, and low ion‐immigration‐energy perovskite can be obtained by releasing stress. Finally, 21.89% efficiency is obtained and the cell can remain almost 97% of the initial efficiency after 5 days.

Abstract

The mixed halide perovskites have become famous for their outstanding photoelectric conversion efficiency among new‐generation solar cells. Unfortunately, for perovskites, little effort is focused on stress engineering, which should be emphasized for highly efficient solar cells like GaAs. Herein, polystyrene (PS) is introduced into the perovskite solar cells as the buffer layer between the SnO₂ and perovskite, which can release the residual stress in the perovskite during annealing because of its low glass transition temperature. The stress‐free perovskite has less recombination, larger lattices, and a lower ion migration tendency, which significantly improves the cell's efficiency and device stability. Furthermore, the so‐called inner‐encapsulated perovskite solar cells are fabricated with another PS capping layer on the top of perovskite. As high as a 21.89% photoelectric conversion efficiency (PCE) with a steady‐state PCE of 21.5% is achieved, suggesting that the stress‐free cell can retain almost 97% of its initial efficiency after 5 days of “day cycle” stability testing.

Secondary amine, dimethylamine is intentionally included in MAPbI₃ perovskite to improve the rigidity and steric hindrance for water adsorption, giving rise to reduced defect density and enhanced hydrophobicity. Solar cells based on this perovskite structure demonstrate a record certified power conversion efficiency of 20.8% for NiO _x ‐based inverted perovskite solar cells and excellent operational stability under continuous light soaking.

Abstract

Large‐bandgap perovskites offer a route to improve the efficiency of energy capture in photovoltaics when employed in the front cell of perovskite–silicon tandems. Implementing perovskites as the front cell requires an inverted (p–i–n) architecture; this architecture is particularly effective at harnessing high‐energy photons and is compatible with ionic‐dopant‐free transport layers. Here, a power conversion efficiency of 21.6% is reported, the highest among inverted perovskite solar cells (PSCs). Only by introducing a secondary amine into the perovskite structure to form MA_{1− x} DMA _x PbI₃ (MA is methylamine and DMA is dimethylamine) are defect density and carrier recombination suppressed to enable record performance. It is also found that the controlled inclusion of DMA increases the hydrophobicity and stability of films in ambient operating conditions: encapsulated devices maintain over 80% of their efficiency following 800 h of operation at the maximum power point, 30 times longer than reported in the best prior inverted PSCs. The unencapsulated devices show record operational stability in ambient air among PSCs.

In article number https://doi.org/10.1002/adma.2019032391903239, Junsheng Yu, Wei Huang, Ziyi Ge, Tobin J. Marks, Antonio Facchetti, and co‐workers present a spontaneous passivation method to greatly improve the performance of perovskite solar cells (PSCs) by using a zwitterionic small‐molecule electrolyte. This bottom‐up passivation is a novel and promising strategy to overcome outstanding issues impeding PSC advances in the future.

The role of DMAI in fabricating high quality CsPbI₃ inorganic perovskite thin films is demonstrated to be a volatile crystal growth additive rather than dopant. With optimal DMAI additive and PTACl passivation, a PTACl‐CsPbI₃ based champion photovoltaic device exhibits a record efficiency of 19.03 %.

Abstract

The controllable growth of CsPbI₃ perovskite thin films with desired crystal phase and morphology is crucial for the development of high efficiency inorganic perovskite solar cells (PSCs). The role of dimethylammonium iodide (DMAI) used in CsPbI₃ perovskite fabrication was carefully investigated. We demonstrated that the DMAI is an effective volatile additive to manipulate the crystallization process of CsPbI₃ inorganic perovskite films with different crystal phases and morphologies. The thermogravimetric analysis results indicated that the sublimation of DMAI is sensitive to moisture, and a proper atmosphere is helpful for the DMAI removal. The time‐of‐flight secondary ion mass spectrometry and nuclear magnetic resonance results confirmed that the DMAI additive would not alloy into the crystal lattice of CsPbI₃ perovskite. Moreover, the DMAI residues in CsPbI₃ perovskite can deteriorate the photovoltaic performance and stability. Finally, the PSCs based on phenyltrimethylammonium chloride passivated CsPbI₃ inorganic perovskite achieved a record champion efficiency up to 19.03 %.

Recent progress on additive engineering during perovskite film formation is reported according to the following common categories: Lewis acid, Lewis base, ammonium salts, low‐dimensional perovskites, and ionic liquid. Then, various additive‐assisted strategies for interface optimization are compared. Finally, an outlook on the research trends with respect to additive engineering in perovskite solar cell development is provided.

Abstract

Perovskite solar cells (PSCs) have reached a certified 25.2% efficiency in 2019 due to their high absorption coefficient, high carrier mobility, long diffusion length, and tunable direct bandgap. However, due to the nature of solution processing and rapid crystal growth of perovskite thin films, a variety of defects can form as a result of the precursor compositions and processing conditions. The use of additives can affect perovskite crystallization and film formation, defect passivation in the bulk and/or at the surface, as well as influence the interface tuning of structure and energetics. Here, recent progress in additive engineering during perovskite film formation is discussed according to the following common categories: Lewis acid (e.g., metal cations, fullerene derivatives), Lewis base based on the donor type (e.g., O‐donor, S‐donor, and N‐donor), ammonium salts, low‐dimensional perovskites, and ionic liquid. Various additive‐assisted strategies for interface optimization are then summarized; additives include modifiers to improve electron‐ and hole‐transport layers as well as those to modify perovskite surface properties. Finally, an outlook is provided on research trends with respect to additive engineering in PSC development.

Recent progress on additive engineering during perovskite film formation is reported according to the following common categories: Lewis acid, Lewis base, ammonium salts, low‐dimensional perovskites, and ionic liquid. Then, various additive‐assisted strategies for interface optimization are compared. Finally, an outlook on the research trends with respect to additive engineering in perovskite solar cell development is provided.

Abstract

Perovskite solar cells (PSCs) have reached a certified 25.2% efficiency in 2019 due to their high absorption coefficient, high carrier mobility, long diffusion length, and tunable direct bandgap. However, due to the nature of solution processing and rapid crystal growth of perovskite thin films, a variety of defects can form as a result of the precursor compositions and processing conditions. The use of additives can affect perovskite crystallization and film formation, defect passivation in the bulk and/or at the surface, as well as influence the interface tuning of structure and energetics. Here, recent progress in additive engineering during perovskite film formation is discussed according to the following common categories: Lewis acid (e.g., metal cations, fullerene derivatives), Lewis base based on the donor type (e.g., O‐donor, S‐donor, and N‐donor), ammonium salts, low‐dimensional perovskites, and ionic liquid. Various additive‐assisted strategies for interface optimization are then summarized; additives include modifiers to improve electron‐ and hole‐transport layers as well as those to modify perovskite surface properties. Finally, an outlook is provided on research trends with respect to additive engineering in PSC development.

In article number https://doi.org/10.1002/aenm.2019018631901863, Fang‐Chung Chen and co‐workers use calculations of the Shockley‐Queisser limits under indoor light sources to reveal an unusual bandgap (E _g) zone, in which the dependence of the power conversion efficiencies (PCEs) on the value of E _g exhibits different trends from that under solar irradiation. Therefore, an increase in the Eg of perovskite materials improves the PCEs of perovskite solar cells under indoor lighting conditions.