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All-inorganic perovskite solar cells (PSCs) are attracting considerable attention due to their promising thermal stability, but their inferior power-conversion efficiencies (PCE) hinder their realistic application. Here, we propose an approach through surface modification based on methyl ammonium halide (MAX) for inorganic CsPbI2Br solar cells processed at a low temperature. The combined benefits of the introduced MAX modifier enable the boosting of the power conversion efficiency to 14.8% with an impressive FF of 82.2% in CsPbI2Br PSCs. Our experimental analyses coupled with optical modeling indicate that the incorporated MAX leads to an effective passivation of the surface traps originating from Pb2+ and I− ions in CsPbI2Br and simultaneously mediates the crystallization of CsPbI2Br with slightly enlarged grains and reduced numbers of structural defects and pinhole. As a result, the interfacial trap-assisted recombination is suppressed and the charge extraction is promoted. Mechanistically, we show that in the presence of MAX, the deep-level traps in the perovskites are passivated, leaving the energy of the trapping centers to become shallower. In this situation, the negative impacts of the traps on carrier transport and recombination are mitigated. [ABSTRACT FROM AUTHOR]

A comprehensive study unveiling the impact of heterovalent doping with Bi3+ on the structural, semiconductive, and photoluminescent properties of a single crystal of lead halide perovskites (CH3NH3PbBr3) is presented. As indicated by single‐crystal XRD, a perfect cubic structure in Bi3+‐doped CH3NH3PbBr3 crystals is maintained in association with a slight lattice contraction. Time‐resolved and power‐dependent photoluminescence (PL) spectroscopy illustrates a progressively quenched PL of visible emission, alongside the appearance of a new PL signal in the near‐infrared (NIR) regime, which is likely to be due to energy transfer to the Bi sites. These optical characteristics indicate the role of Bi3+ dopants as nonradiative recombination centers, which explains the observed transition from bimolecular recombination in pristine CH3NH3PbBr3 to a dominant trap‐assisted monomolecular recombination with Bi3+ doping. Electrically, it is found that the mobility in pristine perovskite crystals can be boosted with a low Bi3+ concentration, which may be related to a trap‐filling mechanism. Aided by temperature (T)‐dependent measurements, two temperature regimes are observed in association with different activation energies (Ea) for electrical conductivity. The reduction of Ea at lower T may be ascribed to suppression of ionic conduction induced by doping. The modified electrical properties and NIR emission with the control of Bi3+ concentration shed light on the opportunity to apply heterovalent doping of perovskite single crystals for NIR optoelectronic applications. Infiltrating single crystals: Heterovalent doping with Bi3+ (see figure) leads to modulation of the charge carrier mobility and thermal activation energy of electrical conductivity in CH3NH3PbBr3 single crystals. Upon doping, a new photoluminescent emission appears in the near‐infrared region of the spectrum. [ABSTRACT FROM AUTHOR]

Reaching the full potential of solar cells based on photo‐absorbers of organic‐inorganic hybrid perovskites requires highly efficient charge extraction at the interface between perovskite and charge transporting layer. This demand is generally challenged by the presence of under‐coordinated metal or halogen ions, causing surface charge trapping and resultant recombination losses. These problems can be tackled by introducing a small molecule interfacial anchor layer based on dimethylbiguanide (DMBG). Benefitting from interactions between the nitrogen‐containing functional groups in DMBG and unsaturated ions in CH3NH3PbI3 perovskites, the electron extraction of TiO2 is dramatically improved in association with reduced Schottky–Read–Hall recombination, as revealed by photoluminescence spectroscopy. As a consequence, the power conversion efficiency of CH3NH3PbI3 solar cells is boosted from 17.14 to 19.1 %, showing appreciably reduced hysteresis. The demonstrated molecular strategy based on DMBG enables one to achieve meliorations on key figures of merit in halide perovskite solar cells with improved stability. Surface traps: Incorporating a dimethylbiguanide (DMBG) anchoring layer in between the compact TiO2 and perovskite photo‐absorber leads to an effective passivation of surface traps with reduced Shockley–Read–Hall recombination, such that the power conversion efficiency of CH3NH3PbI3 solar cells is boosted to 19.1 %. [ABSTRACT FROM AUTHOR]

Thermoelectrochemical (TEC) materials are newly developed energy materials, which are promising and cost-effective in harvesting waste thermal energy based on redox electrolytes. However, liquid-state electrolytes and low thermoelectric (TE) performance seriously limit their application. Here, we report the first gel-state TEC (gel-TEC) materials based on incorporating Sn2+/Sn4+ electrolytes into polymer/single-wall carbon nanotube (SWCNT) composites. A porous 3D network morphology is observed, and the effect of SWCNT content on the tensile mechanical properties and TE performance is studied. Due to their large Seebeck coefficients and significantly enhanced electrical conductivities (10.5 ± 0.8 S m−1), the power factor at room temperature can reach 13.5 ± 3.0 μW m−1 K−2, greater than those of liquid-state TEC materials and possibly the highest for gel-TEC materials. The gel-state, outstanding mechanical properties and excellent TE performance of the gel-TEC materials will speed up and widen their application in various fields such as flexible devices, wearable electronics, e-skins, etc. [ABSTRACT FROM AUTHOR]

2D perovskite structures have gained significant attention due to their reliable long‐term stability. Unlike quasi‐2D perovskites, phase‐pure 2D perovskites exhibit a flattened energy landscape and low energy transfer losses, offering substantial benefits for enhancing device efficiency and stability. Recent research on phase‐pure 2D perovskites has shown significant progress, attributed to their unique properties. This review delineates advancements in the study of phase‐pure 2D perovskite materials and elucidates the relationships between crystal structure design, growth, and device performance regulation. Additionally, it summarizes techniques for characterizing phase‐pure 2D structures and methods for their precise synthesis. Finally, an outlook on the future development of phase‐pure 2D perovskites, highlighting the scientific and technological challenges in current research is provided. [ABSTRACT FROM AUTHOR]

Lewis base molecules are widely used to passivate structural defects in perovskites. However, the spatial compatibility between these molecules and the perovskite lattice is seldom considered. Herein, a multisite atomic‐oxygen (O) anchoring passivation strategy using 1,1,2,2‐tetra(4‐methoxyphenyl)ethene (TMPE), which contains four electronegative O atoms to selectively anchor iodine vacancies and passivate under‐coordinated Pb2+ or MA+ defects is proposed. It is found that the distance between any three O atoms in a TMPE molecule matches that of iodine ions in the lattice structure, thereby maximizing passivation effects and enhancing lattice stability. Additionally, the coordination of TMPE facilitates the formation of larger colloid sizes in the precursor solution, effectively regulating crystal growth. Due to the molecular extrusion effect, TMPE‐based anchors localize on the surface, passivating defects and mitigating nonradiative recombination. As a result, defects in MA‐based and FA‐based perovskite films are significantly reduced, achieving optimized power conversion efficiencies (PCEs) of 19.9% and 24.5%, while exhibiting exceptional stability by retaining 90% of initial PCE after 1200 h of storage without encapsulation. This single molecule‐controlled perovskite multisite anchoring strategy would help resolve lattice stability issue caused by perovskite defects, thereby paving the pathway for the development of high‐performance and highly stable perovskite solar cells. [ABSTRACT FROM AUTHOR]

All-inorganic perovskite solar cells (PSCs) are attracting considerable attention due to their promising thermal stability, but their inferior power-conversion efficiencies (PCE) hinder their realistic application. Here, we propose an approach through surface modification based on methyl ammonium halide (MAX) for inorganic CsPbI2Br solar cells processed at a low temperature. The combined benefits of the introduced MAX modifier enable the boosting of the power conversion efficiency to 14.8% with an impressive FF of 82.2% in CsPbI2Br PSCs. Our experimental analyses coupled with optical modeling indicate that the incorporated MAX leads to an effective passivation of the surface traps originating from Pb2+ and I- ions in CsPbI2Br and simultaneously mediates the crystallization of CsPbI2Br with slightly enlarged grains and reduced numbers of structural defects and pinhole. As a result, the interfacial trap-assisted recombination is suppressed and the charge extraction is promoted. Mechanistically, we show that in the presence of MAX, the deep-level traps in the perovskites are passivated, leaving the energy of the trapping centers to become shallower. In this situation, the negative impacts of the traps on carrier transport and recombination are mitigated.

A comprehensive study unveiling the impact of heterovalent doping with Bi 3+ on the structural, semiconductive, and photoluminescent properties of a single crystal of lead halide perovskites (CH 3 NH 3 PbBr 3 ) is presented. As indicated by single-crystal XRD, a perfect cubic structure in Bi 3+ -doped CH 3 NH 3 PbBr 3 crystals is maintained in association with a slight lattice contraction. Time-resolved and power-dependent photoluminescence (PL) spectroscopy illustrates a progressively quenched PL of visible emission, alongside the appearance of a new PL signal in the near-infrared (NIR) regime, which is likely to be due to energy transfer to the Bi sites. These optical characteristics indicate the role of Bi 3+ dopants as nonradiative recombination centers, which explains the observed transition from bimolecular recombination in pristine CH 3 NH 3 PbBr 3 to a dominant trap-assisted monomolecular recombination with Bi 3+ doping. Electrically, it is found that the mobility in pristine perovskite crystals can be boosted with a low Bi 3+ concentration, which may be related to a trap-filling mechanism. Aided by temperature (T)-dependent measurements, two temperature regimes are observed in association with different activation energies (E a ) for electrical conductivity. The reduction of E a at lower T may be ascribed to suppression of ionic conduction induced by doping. The modified electrical properties and NIR emission with the control of Bi 3+ concentration shed light on the opportunity to apply heterovalent doping of perovskite single crystals for NIR optoelectronic applications., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reaching the full potential of solar cells based on photo-absorbers of organic-inorganic hybrid perovskites requires highly efficient charge extraction at the interface between perovskite and charge transporting layer. This demand is generally challenged by the presence of under-coordinated metal or halogen ions, causing surface charge trapping and resultant recombination losses. These problems can be tackled by introducing a small molecule interfacial anchor layer based on dimethylbiguanide (DMBG). Benefitting from interactions between the nitrogen-containing functional groups in DMBG and unsaturated ions in CH 3 NH 3 PbI 3 perovskites, the electron extraction of TiO 2 is dramatically improved in association with reduced Schottky-Read-Hall recombination, as revealed by photoluminescence spectroscopy. As a consequence, the power conversion efficiency of CH 3 NH 3 PbI 3 solar cells is boosted from 17.14 to 19.1 %, showing appreciably reduced hysteresis. The demonstrated molecular strategy based on DMBG enables one to achieve meliorations on key figures of merit in halide perovskite solar cells with improved stability., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)