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Perovskite solar cells (PSCs) with state-of-the-art efficiencies contain thermally unstable methylammonium (MA). Avoiding MA molecules usually leads to a severe decrease in the cell efficiency. In this work, a novel ion liquid (simplified as NDAPBF4) possessing a pyridine cation and BF4− anion were introduced to improve the performance of MA-free PSCs. The ion liquid NDAPBF4 can optimize the grain growth of the perovskite, leading to reduced carrier traps. In particular, NDAPBF4 served as an n-type dopant and boosted the electron transportation in the perovskite films, which further suppressed the carrier non-radiative recombination at the interface between the perovskite and the electron transporting layer. Finally, PSCs with a Cs0.05FA0.95PbI3 perovskite film as the absorber achieved a remarkable efficiency of 21.25%, which was one of the highest MA-free inverted perovskite solar cells up to date. PSCs doped with NDAPBF4 also gave excellent stability, which preserved 95% and 94% of the initial efficiency after being aged for 1000 h and 500 h under room temperature and elevated temperature at 85 °C, respectively.

Employing low-dimensional perovskite has been proven to be a promising approach to enhance the efficiency and stability of perovskite solar cells. Here, thiopheniformamidine hydrochloride is introduced into CH

Conjugated polyelectrolytes (CPEs) have been successfully applied in organic photovoltaics and organic light-emitting diodes, and recently those with inorganic cations became to serve as a hole-transporting layer (HTL) in inverted perovskite solar cells (iPSCs), whereas the CPE HTL materials with organic cations are really limited. In this work, we design a CPE whose side-chains are end-capped by CH3NH3+ cations, the same cations as that in the perovskite layer. The CPE is found to be more compatible to the perovskite material, and shows stronger abilities to reduce the traps both at the surface and in the bulk of the perovskite layer, compared with the typical poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). The resulting iPSC presents much improved photovoltaic properties and a better long-term stability, with a power conversion efficiency of 19.76%, which is the highest value ever reported for iPSCs based on CPE HTLs.

Here, the authors report a highly efficient integrated ideal-bandgap perovskite/bulk-heterojunction solar cell (IPBSC) with an inverted architecture, featuring a near infrared (NIR) polymer DTBTI-based bulk-heterojunction (BHJ) layer atop guanidinium bromide (GABr)-modified FA

Quasi-two-dimensional (Q-2D) perovskites ((RNH3)2MAn−1PbnI3n+1, RNH3 represents the organic spacer (mostly phenethylammonium (PEA) and n-butylammonium (BA)) and MA = methylammonium) have shown great potential for application in solar cells due to their intrinsic stability, where the organic spacer dominantly determines the Q-2D perovskite ambient stability and device performance. Current studies merely concentrate on unary organic spacer Q-2D perovskites, either using BA or PEA. Herein, for the first time, we have successfully designed and fabricated (PEA1−xBAx)2MA3Pb4I13 binary spacer-based Q-2D perovskite films, and demonstrated that the device using binary organic spacer-based Q-2D perovskite films has substantially better performance than that using either of the unary organic spacer-based Q-2D perovskite films. The (PEA0.8BA0.2)2MA3Pb4I13 binary spacer device yields a maximum power conversion efficiency of 15.7%, which outperforms the efficiency record (12–14%) for unary spacer (PEA or BA) Q-2D perovskite devices. In particular, a peak open-circuit voltage of 1.21 V is achieved due to a non-radiative recombination loss of ∼100 mV, the lowest reported loss value for Q-2D perovskite devices. The high device performance results from binary-spacer-induced intensified film surface quality, preferable vertical orientation of crystals and improved film optoelectronic properties as well as obviously decreased device recombination losses. These findings open up a new avenue for the rational design of Q-2D perovskite materials with polynary organic spacer.

Although great efforts have been devoted to enhancing the efficiency and stability of perovskite solar cells (PSCs), the performance of PSCs has been far lower than anticipated. Interface engineering is helpful for obtaining high efficiency and stability through control of the interfacial charge transfer in PSCs. This paper demonstrates that the efficiency and stability of PSCs can be enhanced by introducing stable α-CsPbI3 quantum dots (QDs) as an interface layer between the perovskite film and the hole transport material (HTM) layer. By synergistically controlling the valence band position (VBP) of the perovskite and the interface layer, an interface engineering strategy was successfully used to increase the efficiency of hole transfer from the perovskite to the HTM layer, resulting in the power conversion efficiency increasing from 15.17 to 18.56%. In addition, the enhancement of the stability of PSCs can be attributed to coating inorganic CsPbI3 QDs onto the perovskite layer, which have a high moisture stability and result in long-term stability of the PSCs in ambient air.

Exploring competent electrocatalysts for the oxygen evolution reaction (OER) is central to the development of a clean, reliable and emission-free hydrogen economy. Perovskites have been seen as promising OER electrocatalysts among all the potential candidates so far. Here, we introduced redox inactive Zr and Y ions to meliorate the redox capability of active ions and prepared BaCo0.5−xFe0.5−xZrxYxO3−δ (BCF(ZY)x, x = 0.0−0.2) oxides as efficient electrocatalysts for the OER. The catalyst of BCF(ZY)0.1 exhibits a higher OER activity (including disk activity, intrinsic activity and mass activity) and better durability than the gold-standard OER electrocatalyst IrO2 and the well-known Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite. The overpotential to deliver an electrode current density of 10 mA cm−2 of BCF(ZY)0.1 oxide is merely 0.32 V in 1 M KOH, and the intrinsic activity of BCF(ZY)0.1 is ∼52 times higher than IrO2. The outstanding electro-catalytic activity and stability of BCF(ZY)0.1 are attributed to the increased redox ability compared with BSCF, including the faster charge transfer process and much more facile adsorption of OH− and desorption of O2.

A delicate control of crystallization and morphology of perovskite absorbers is critical to obtain high performance hybrid perovskite solar cells (PSCs). Here, we have developed a novel crystallization strategy which involves hydration water induced intermediate phase formation under heat assisted spin-coating processing (HASP) to manipulate the morphology and grain size of perovskite films, and thus it can avoid the use of toxic and volatile antisolvents used in conventional one-step solution processes to make PSCs. During HASP, impressive morphological evolution of films occurs with the formation of CH3NH3PbI3·xH2O perovskite intermediate phases. With ingenious control of the crystallization kinetics, highly crystalline perovskite films with fewer defect states and high carrier lifetimes are obtained. The corresponding PSCs exhibit a power conversion efficiency (PCE) of 19.12% with a stabilized power output efficiency of 18.89% at the maximum power point, which is a 70% enhancement compared to that of conventional one-step process based PSCs. Furthermore, the PSC fabricated by the HASP method achieved a PCE of 15.47% with an active area of 1.2 cm2. Moreover, the flexible PSCs fabricated by the HASP method achieved a record efficiency of 14.87% with negligible hysteresis for PEDOT:PSS-based flexible inverted PSCs. Our work opens up a new avenue for morphology and crystallization control through hydration water induced intermediate phase formation under HASP, which paves the way toward further enhancing the device performance of perovskite solar cells.

Side-chain polymers have the potential to be excellent dopant-free hole-transporting materials (HTMs) for perovskite solar cells (PSCs) because of their unique characteristics, such as tunable energy levels, high charge mobility, good solubility, and excellent film-forming ability. However, there has been less research focusing on side-chain polymers for PSCs. Here, two side-chain polystyrenes with triphenylamine substituents on carbazole moieties were designed and characterized. The properties of the side-chain polymers were tuned finely, including the photophysical and electrochemical properties and charge mobilities, by changing the positions of triphenylamine substituents on carbazole. Owing to the higher mobility and charge extraction ability, the polymer P2 with the triphenylamine substituent on the 3,6-positions of the carbazole unit showed higher performance with power conversion efficiency (PCE) of 18.45%, which was much higher than the PCE (16.78%) of P1 with 2,7-positions substituted. These results clearly demonstrated that side-chain polymers can act as promising HTMs for PSC applications and the performance of side-chain polymers could be optimized by carefully tuning the structure of the monomer, which provides a new strategy to design new kinds of side-chain polymers and obtain high-performance dopant-free HTMs.

An optimized charge transporting layer (CTL) under perovskite film is crucial for efficient photoelectric devices. Here, a new water-soluble conjugated polyeletrolyte (CPE) with CH3 NH3+ (MA+ ) counterion termed as TB(MA) is used as the hole transporting layer (HTL) instead of the acidic poly(3,4-ethylenedioxythiophene):poly-styrene sulfonate (PEDOT:PSS) in sky-blue perovskite light-emitting diodes (PeLEDs). The inherent hydrophilicity of CPE enables a well-growth of quasi-2D perovskite layer with uniform and compact morphology, enhanced crystallinity with rare defect density and excellent energy transfer, resulting in a high photoluminescence quantum yield (PLQY) up to 62.0%. Especially, the MA+ counterion is able to passivate the interfacial defects in the perovskite, which optimize the interfacial compatibility between HTL and perovskite film. Finally, efficient sky-blue PeLEDs, emitting at 488 nm, are fabricated with high external quantum efficiency (EQE) up to 13.5% by using CPE as HTL. In addition, due to the low-temperature processability of water-soluble CPE, an efficient flexible sky-blue PeLEDs based on PEN/ITO substrate is also obtained with high EQE of 8.3%. Using CPE as HTL is an effective strategy toward fabricating efficient blue PeLEDs.

Hard carbon exhibits high theoretical capacity for sodium-ion batteries. However, its practical application suffers from low electric conductivity, poor electrochemical stability, and sluggish kinetics. To tackle these challenges, novel nitrogen-doped carbon spheres with mesopores, ultrathin nanostructure, and optimal graphitization are prepared by a three-step procedure. We find that the as-prepared sample (NMCSs-800) with an optimal structure and nitrogen content delivers a high reversible sodium storage capacity of 334.7 mA h/g at 50 mA/g and an ultrahigh rate performance of 93.9 mA h/g at 5 A/g, which is better than most state-of-the-art carbon materials. The improved energy storage capacity is attributed to its unique architecture and optimal nitrogen doping, which provide abundant active sites, defects, and voids. Moreover, kinetic analysis and in situ Raman spectroscopy results reveal adsorption and adsorption-intercalation mechanisms for Na

Modified 3,4-ethylenedioxythiophene is employed as the conjugated side chain in conjugated polymers, which can significantly depress the dark current of the polymer photodetectors with little associated decrease in photovoltaic properties, thus enhanceing the detectivities. This approach can be applied to a variety of conjugated polymers covering a photoresponse range from UV to NIR.

The surface defects and grain boundary defects of organometallic halide perovskite films are detrimental to both the efficiency and stability of perovskite solar cells (PSCs). Furthermore, the electrical conductivity, work function and surface morphology of the hole transport layer (HTL) can also affect the performance of PSCs significantly. Here, we first have developed a novel synergistic strategy that uses multiple functional EMIC (1-Ethyl-3-methylimidazolium chloride) ionic liquid to modify PEDOT:PSS (poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate) HTL, thereby obtaining the HTL with high electrical conductivity, low work function and smooth surface. Moreover, a novel S-acetylthiocholine chloride molecule which replaces expensive PCBM (phenyl-C61-butyric acid methyl ester) is developed to effectively passivate the negative- and positive-charged ionic defects in hybrid perovskite. The synergistic strategy extends the carrier recombination lifetime and reduces the charge trap density. In addition, the current hysteresis of the inverted device was also effectively eliminated. As a result, the champion cell in small area shows 20.06% efficiency with no hysteresis, along with an efficiency 18.77% for inverted PSCs in an active area of 1 cm2, both of which are the highest efficiency in the one-step PEDOT:PSS-based inverted PSCs so far. Compared to PCBM, the device passivated by S-acetylthiocholine chloride also has improved environmental stability (retaining 85% of initial PCE after 35 days storage without encapsulation in air with 60% humidity) and thermal stability (retaining 87% of initial PCE after 80 °C for 24 h storage without encapsulation under inert atmosphere).

A variety of dopant-free hole-transporting materials (HTMs) is effectively applied in perovskite solar cells (PSCs); however, HTMs with the additional function of HTM/perovskite interfacial optimization that is crucial to their photovoltaic performance are really limited. In this work, the design of an HTM bearing an intensive exposure of its functional aromatic rings to perovskite layer via side-chain engineering is attempted. With an edge-on orientation and a short distance to perovskite, this HTM was expected to display an excellent ability to extract holes from and passivate defects in the perovskite layer. To demonstrate this strategy, an alternating copolymer was constructed with a 2,5-di-2-ethylhexyloxy-1,4-phenylene unit and a bithiophene unit, and the PSC based on this polymer showed an ultrahigh short-circuit current density of 25.50 mA cm-2 , which was the highest so far presented by dopant-free organic HTMs. A comparable power conversion efficiency of 19.68% (certified: 19.5%) to that of a control 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) device (19.81%) was thus obtained, which is the highest value ever reported for mesoporous PSCs based on dopant-free polymeric HTMs.