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Recently, mixed‐cation halide perovskites have gained significant attention for developing stable, high‐performance solar cells. However, their nonlinear optical (NLO) properties are much less explored. Herein, this study reports on intriguing NLO properties observed from FA0.8MA0.2PbI3 single crystals, having an ideal bandgap of 1.52 eV for photovoltaic performance. Contrary to a simple prediction, the perovskite exhibits higher‐order multiphoton absorption (MPA) over a broad wavelength range from 1300 to 1710 nm as evidenced by wavelength‐ and intensity‐dependent photoluminescence measurements. The corresponding MPA coefficients are very large to dominate lower‐order ordinary MPA across the bandgap. The hexagonal phase present in the perovskite is responsible for the observed higher‐order transition as confirmed by the recovery of ordinary MPA in the absence of the hexagonal phase. Although the perovskite is known to crystallize into the cubic phase at room temperature, these results indicate that minor inclusion of the hexagonal phase (≈4.0% at room temperature) can drastically alter the nature of the multiphoton process by double resonance uniquely offered by the mixed phases. [ABSTRACT FROM AUTHOR]

Recently, mixed‐cation halide perovskites have gained significant attention for developing stable, high‐performance solar cells. However, their nonlinear optical (NLO) properties are much less explored. Herein, this study reports on intriguing NLO properties observed from FA0.8MA0.2PbI3 single crystals, having an ideal bandgap of 1.52 eV for photovoltaic performance. Contrary to a simple prediction, the perovskite exhibits higher‐order multiphoton absorption (MPA) over a broad wavelength range from 1300 to 1710 nm as evidenced by wavelength‐ and intensity‐dependent photoluminescence measurements. The corresponding MPA coefficients are very large to dominate lower‐order ordinary MPA across the bandgap. The hexagonal phase present in the perovskite is responsible for the observed higher‐order transition as confirmed by the recovery of ordinary MPA in the absence of the hexagonal phase. Although the perovskite is known to crystallize into the cubic phase at room temperature, these results indicate that minor inclusion of the hexagonal phase (≈4.0% at room temperature) can drastically alter the nature of the multiphoton process by double resonance uniquely offered by the mixed phases. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) hybrid perovskites with novel functionalities and structural diversity are a perfect platform for emerging optoelectronic devices such as photodetectors, light‐emitting diodes, and solar cells. Here, we demonstrate that excess concentration of Cesium bromide (CsBr) is key to the formation of easily exfoliated 2D Cs2Cu(Cl/Br)4 perovskite crystal. Furthermore, by employing this trick to 2D perovskite MA2Cu(Cl/Br)4 (MA=methylammonium), we achieve a phase‐pure easily exfoliated 2D mixed‐cation (MA/Cs)2Cu(Cl/Br)4 perovskite crystal, which exhibits reduced bandgap (1.53 eV) with ferromagnetic behavior and photovoltaic property. The resultant mixed‐cation structured device reveals enhanced efficiency compared to all MA and all Cs counterparts. These findings demonstrate the importance of cation‐engineering in developing innovative materials with novel properties. [ABSTRACT FROM AUTHOR]

Photodetectors convert optical signals into electrical signals and demonstrate application potential in various fields, such as optical communication, image detection, environmental monitoring, and optoelectronics. In this study, a mixed cation–halide perovskite-based ultraviolet C photodetector was fabricated using a solution process. The higher the mobility of the perovskite carrier, which is one of the factors affecting the performance of electronic power devices, the better the carrier diffusion. The on/off ratio and responsivity indicate the sensitivity of the response, and together with the detectivity and external quantum efficiency, these parameters demonstrate the performance of the detector. The detector fabricated in this study exhibited a mobility of 202.2 cm2/Vs and a high on/off ratio of 105% at a −2 V bias, under 254 nm light irradiation with an intensity of 0.6 mW/cm2. The responsivity, detectivity, and external quantum efficiency of the as-fabricated detector were 5.07 mA/W, 5.49 × 1011 Jones, and 24.8%, respectively. These findings demonstrate that the solution process employed in this study is suitable for the fabrication of mixed cation–halide perovskites which show immense potential for use as photodetectors. [ABSTRACT FROM AUTHOR]

Mixed cation strategy greatly benefits the enhancement of device performance and chemical stability. However, adverse impact also accompanies the mixed cation system simultaneously. It brings the compositional instability, wherein the homogeneous film is likely to segregate into multi-phases during the fabrication and ageing process, thus resulting in the efficiency reduction of perovskite solar cells (PSCs) devices. This review focuses on the cation induced phase segregation, and elucidates the segregation mechanisms from the perspectives of film formation and ageing process, respectively. Furthermore, the influence of cation segregation on device performance and operational stability are discussed. And based on these understandings, viable strategies are proposed for the design of phase-stable mixed composition halide perovskites and for suppressing segregation to benefit its development towards commercial applications.

Photodetectors convert optical signals into electrical signals and demonstrate application potential in various fields, such as optical communication, image detection, environmental monitoring, and optoelectronics. In this study, a mixed cation–halide perovskite-based ultraviolet C photodetector was fabricated using a solution process. The higher the mobility of the perovskite carrier, which is one of the factors affecting the performance of electronic power devices, the better the carrier diffusion. The on/off ratio and responsivity indicate the sensitivity of the response, and together with the detectivity and external quantum efficiency, these parameters demonstrate the performance of the detector. The detector fabricated in this study exhibited a mobility of 202.2 cm2/Vs and a high on/off ratio of 105% at a −2 V bias, under 254 nm light irradiation with an intensity of 0.6 mW/cm2. The responsivity, detectivity, and external quantum efficiency of the as-fabricated detector were 5.07 mA/W, 5.49 × 1011 Jones, and 24.8%, respectively. These findings demonstrate that the solution process employed in this study is suitable for the fabrication of mixed cation–halide perovskites which show immense potential for use as photodetectors.

Perovskite/organic tandem solar cells (POTSCs) are gaining attention due to their easy fabrication, potential to surpass the S-Q limit, and superior flexibility. However, the low power conversion efficiencies (PCEs) of wide bandgap (Eg) perovskite solar cells (PVSCs) have hindered their development. This work presents a novel and effective mixed-cation passivation strategy (CE) to passivate various types of traps in wide-Eg perovskite. The complementary effect of 4-trifluoro phenethylammonium (CF 3 -PEA + , denoted as CA + ) and ethylenediammonium (EDA 2+ , denoted as EA 2+ ) reduces both electron/hole defect densities and non-radiative recombination rate, resulting in a record open-circuit voltage (V oc ) of wide-Eg PVSCs (1.35 V) and a high fill factor (FF) of 83.29%. These improvements lead to a record PCE of 24.47% when applied to fabricated POTSCs, the highest PCE to date. Furthermore, unencapsulated POTSCs exhibit excellent photo and thermal stability, retaining over 90% of their initial PCE after maximum power point (MPP) tracking or exposure to 60 °C for 500 h. These findings imply that the synergic effect of surface passivators is a promising strategy to achieve high-efficiency and stable wide-Eg PVSCs and corresponding POTSCs., (© 2023 Wiley-VCH GmbH.)

Abstract Two glass series were developed based on the substitution of a monovalent glass modifier for a di- or trivalent ion in a high borate glass system. The BRS series consists of compositions 0.70 B 2 O 3 –0.30-X Rb 2 O – X SrO, and the BRG series consists of compositions 0.70 B 2 O 3 –0.30-X Rb 2 O – X Ga 2 O 3 , where 0.00 ≤ X ≤ 0.10 in increments of 0.2. All glasses were characterized in order to examine their composition-structure-property relationships, and to assess their potential for use as degradable, radiopaque embolic agents. Glasses were melt quenched, and evaluated in terms of structural changes (11B MAS-NMR, density, and glass transition temperature), changes in radiopacity (both CT and MRI), and changes in degradation timeframes under simulated physiological conditions. Structural analysis determined there was no change in the B4% of the BRS series, despite a linear increase in density and Tg. The strontium acts as a crosslinker, creating a more hydrolytically stable network, which leads to longer dissolution times. Conversely, the BRG series displayed a linear decrease in the B4%, a decrease in density (Tg data not available), yet a slight increase in hydrolytic stability is also observed. Gallium most likely acts more as a glass former than a glass modifier, thereby sequestering oxygens from the tetrahedral boron centers, creating trigonal B3 centers and tetrahedral gallium. All glasses were found to be imageable on CT (intensity > 3200 HU at 120 kVp), and invisible on clinical MR imaging modalities. Highlights • Borate glasses offer good degradation and imageability properties for embolization • Changing the composition of the glass system drastically alters its properties • Substituting rubidium for strontium significantly decreases hydrolytic degradation • All glass series studied demonstrated good contrast on computed tomography imaging • The strontium series studied shows promise as a new transarterial embolic agent [ABSTRACT FROM AUTHOR]

A new hole transporting material based on 3,6-disubstituted carbazole (3,6Cz-TPA) was synthesized through a one-step approach and was used as hole-transporting material in perovskite solar cells. The HTM exhibits molecular glass behavior and a high glass transition temperature of 146 °C. A hole-mobility of 7.0 × 10−6 cm2 V−1 s−1 has been measured which is slightly lower than the mobility of spiro-OMeTAD (2.5 × 10−5 cm2 V−1 s−1). The HOMO energy level, similar to the HOMO of spiro-OMeTAD, is suitable to allow the hole injection from the perovskite. Solar cells based on organic-inorganic hybrid cation perovskite light absorber have been built. The optimization of the concentration of the HTM shows an optimal concentration around 30 mM. Finally, the perovskite cells based on 3,6Cz-TPA as HTM lead to a power conversion efficiency around 16%, similar to the most commonly used spiro-OMeTAD (17%). [ABSTRACT FROM AUTHOR]

Hybrid organolead halide perovskites, a class of materials used in optoelectronic devices, have attracted significant attention due to their performance and fabrication process. This paper reports on a pinhole free, compact, high-quality, mixed-cation (consisting of formamidinium (FA) and methylammonium (MA)) FA x MA (1− x ) PbI 3 polycrystalline perovskite film prepared in a one-step solution process using a doctor-blading deposition technology under ambient conditions with no subsequent annealing. A perovskite film domain size of up to 100 μm was obtained. A FA x MA (1− x ) PbI 3 -based photodetector using a simplestructure glass/FA x MA (1− x ) PbI 3 /Au device was fabricated. Ultraviolet (UV) high photoresponse reached the near-infrared (NIR) range. Its best responsivity (R) was 10.57 AW -1 with a response speed of ∼9.0 ms. Results indicate that this technique results in high-quality, phase-pure, FA x MA (1− x ) PbI 3 perovskite films and high-performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

Mixed cation hybrid perovskites such as Cs xFA1− xPbI3 are promising materials for solar cell applications, due to their excellent photoelectronic properties and improved stability. Although power conversion efficiencies (PCEs) as high as 18.16% have been reported, devices are mostly processed by the anti-solvent method, which is difficult for further scaling-up. Here, a method to fabricate Cs xFA1− xPbI3 by performing Cs cation exchange on hybrid chemical vapor deposition grown FAPbI3 with the Cs+ ratio adjustable from 0 to 24% is reported. The champion perovskite module based on Cs0.07FA0.93PbI3 with an active area of 12.0 cm2 shows a module PCE of 14.6% and PCE loss/area of 0.17% cm−2, demonstrating the significant advantage of this method toward scaling-up. This in-depth study shows that when the perovskite films prepared by this method contain 6.6% Cs+ in bulk and 15.0% at the surface, that is, Cs0.07FA0.93PbI3, solar cell devices show not only significantly increased PCEs but also substantially improved stability, due to favorable energy level alignment with TiO2 electron transport layer and spiro-MeOTAD hole transport layer, increased grain size, and improved perovskite phase stability. [ABSTRACT FROM AUTHOR]

A facile one-pot synthesis method is developed for preparing mixed-cation Cs 1− x FA x PbI 3 PQDs at a low temperature of 60 °C in open air without vacuum and inert atmospheres. This one-pot synthesis allows fine-tuning of the A-site cations of the PQDs, enabling the control of crystal structures and optical properties, thus optimizing photovoltaic performance. [Display omitted] • One-pot synthesis of mixed-cation Cs 1 − x FAxPbI3 PQDs is developed at 60 °C in open air. • The A-site cations of Cs 1 − x FAxPbI3 PQDs can be fine-tuned by adjusting the precursor ratio. • The fine tunability allowed the control of optical properties and crystal structures of the PQDs. • The PQD solar cells can also be systematically optimized to exhibit high PCEs and stability. • DFT and DFPT calculations at finite temperatures provide a thermodynamic proof for the synthesis. Cesium-formamidinium (FA) lead triiodide (Cs 1− x FA x PbI 3) perovskite quantum dots (PQDs) are promising building blocks for photovoltaics. However, the mixed-cation colloidal PQDs are difficult to be synthesized in one pot because of the differences in optimal reaction temperatures of Cs (180 °C) and FA (80 °C) precursors; therefore, they are obtained by cation-exchange reactions between pre-synthesized CsPbI 3 and FAPbI 3 PQDs. Herein, one-pot synthesis of Cs 1− x FA x PbI 3 PQDs is developed at 60 °C in open air, dramatically reducing the process time and energy consumption compared to the conventional cation-exchange method. Computational calculations considering temperature effects reveal that the formation of mixed-cation PQDs is thermodynamically favorable even at the low synthesis temperature. The temperature effects dominate the mixing energy over the configurational entropy effect as the temperature increased, and thus Cs crystallizes more easily than FA at the synthesis temperature. This one-pot synthesis also allows fine-tuning of the A-site cations of Cs 1− x FA x PbI 3 PQDs, enabling the control of crystal structures and optical properties, thus optimizing photovoltaic performance. As a result, the fabricated Cs 1− x FA x PbI 3 PQD solar cells exhibit power conversion efficiencies (PCEs) up to 11.58 %, which is the highest among the reported solar cells fabricated using QDs synthesized at ≤ 60 °C in open air. The optimized solar cell retains 92 % of its initial PCE value after 1,083 h in dry air (dark and relative humidity < 10 %). [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have been attracted the attention of many researchers due to their high conversion efficiency, low manufacturing cost, easy manufacturing steps, high light absorption, and the possibility of changing the photo electronic properties by modifying the chemical structure. Despite the mentioned advantages, the low stability of PSCs and toxicity of lead in the perovskite layer were the challenging issues in this field. In this regard, the use of mixed cation and mixed halide perovskite compounds with high crystal quality, efficiency, and stability has attracted enormous attention. In this project, Fe2+, Cd2+, and Cs+ cations with various contents (Fe2+ + Cd2+: 5% and 10%; Cs+: 5% and 10%) were partially replaced the Pb2+ and CH 3 NH 3 + cations, respectively in the MAPbI 3 perovskite structure through a two-step process using spin-coating. The as-synthesized [Cs y MA 1-y Pb 1-a-b Fe a Cd b I 3-2a Cl 2a ], (a+b): 5, 10%, y: 5, 10%) perovskites were characterized with X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD), and field emission scanning electron microscopy (FESEM). The optical properties of prepared compounds were investigated by ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy. The photovoltaic behavior as well as stability of solar cells containing MAPbI 3 , [Cs y MA 1-y Pb 1-a-b Fe a Cd b I 3-2a Cl 2a ], (a+b): 5%, y: 5%), and [Cs y MA 1-y Pb 1-a-b Fe a Cd b I 3-2a Cl 2a ], (a+b): 10%, y: 10%) perovskites as active layers were evaluated by current density-voltage (I–V) under AM1.5G illumination. Results showed that partial substitution of CH 3 NH 3 + cations with Cs+ and Pb2+ cations with Fe2+ + Cd2+ in the CH 3 NH 3 PbI 3 structure improved crystallinity and photovoltaic parameters. The average power conversion efficiency (PCE) of six solar cell containing [Cs y MA 1-y Pb 1-a-b Fe a Cd b I 3-2a Cl 2a ], (a+b): 10%, y: 10%) perovskite layer was 21.04% which was 1.03 and 1.21 times higher than that cells containing [Cs y MA 1-y Pb 1-a-b Fe a Cd b I 3-2a Cl 2a ], (a+b): 5%, y: 5%) and MAPbI 3 , respectively. The electrochemical impedance spectroscopy (EIS) was utilized to study the charge transfer resistance (R ct) and recombination resistance (R rec) of prepared solar cells. The R ct and R rec values of fabricated solar cell were decreased and increased, respectively in the presence of Fe2+, Cd2+, and Cs+ inorganic cations. As a result, the [Cs y MA 1-y Pb 1-a-b Fe a Cd b I 3-2a Cl 2a ] perovskites can be considered as the appropriate candidate with high efficiency, stability, and low lead content in the planar perovskite solar cells. [Display omitted] • Fe2+ + Cd2+ and Cs+ cations were partially replaced Pb2+ and MA+ in MAPbI 3 structure, respectively. • Maximum PCE of 21.11% is obtained in cell containing [Cs y MA 1-y Pb 1-a-b Fe a Cd b I 3-2a Cl 2a ], (a+b): 10%, y: 10%) perovskite layer. • Stability of MAPbI 3 -based cell improved in the presence of Fe2+, Cd2+, and Cs+ inorganic cations. [ABSTRACT FROM AUTHOR]

The effect of increasing substitutions of La 2 O 3 :Na 2 O on the structure ( 11 B MAS NMR) and properties, specifically strontium (Sr) ion release from five quaternary borate glass compositions (B 2 O 3 –SrO–Na 2 O–La 2 O 3 ) was studied. To examine component ion release, samples were extracted under simulated physiological conditions at 37 °C for five extraction time points (24, 72, 168, 336 and 720 h). A linear release profile for strontium was provided by composition LB102 (70B 2 O 3 –20SrO–6Na 2 O–4La 2 O 3 ) for up to 720 h. 11 B MAS NMR was used to investigate the impact of La 2 O 3 :Na 2 O substitution on the boron structure and speciation. Substitutions appeared to have minor effects on borate speciation, with the only change being a decrease in the proportion of BO 4 at maximum La 2 O 3 loading (70B 2 O 3 –20SrO–10La 2 O 3 ). These data further demonstrate the possible utility of high boron glasses as controllable degradable materials for the delivery of therapeutic metal ions, such as strontium. [ABSTRACT FROM AUTHOR]

Formamidinium (FA)-based quasi-two dimensional (Q-2D) perovskite normally has better environmental stability than methylammonium (MA)-based one, however, it is difficult to form larger n (n > 2) phases of layered FA-based perovskite due to their larger formation energies, resulting in insufficient absorption of sunlight and then poor performance of its solar cell. Here we partially replace FA with MA to form (BA) 2 (FA 1- x MA x) 3 Pb 4 I 13 mixture, which contains enriched larger n (n = 3, 4, a n d larger) phases, where BA is butylammonium. Particularly, the (BA) 2 (FA 0.8 MA 0.2) 3 Pb 4 I 13 perovskite film show the best stability under ambient conditions. Furthermore, using inverted planar heterojunction structure, the photovoltaic device based on (BA) 2 (FA 0.8 MA 0.2) 3 Pb 4 I 13 demonstrates power conversion efficiency of 14.2 %, which is among the highest efficiencies for the FA-rich Q-2D perovskites with n ≤ 4. This work highlights that FA-rich Q-2D perovskites have great promise for optoelectronic devices. • (BA) 2 (FA 0.8 MA 0.2) 3 Pb 4 I 13 film was stable in air for more than one month. • (BA) 2 (FA 0.8 MA 0.2) 3 Pb 4 I 13 based solar cell with power conversion efficiency of 14.2 %. • Among the highest efficiencies for FA-rich quasi-2D perovskite with n ≤ 4. [ABSTRACT FROM AUTHOR]

Thin films of polymer electrolytes comprising of PVA and KOH ( A) with and without the addition of zinc salts, viz., zinc acetate ( B) and zinc triflate ( C) as mixed cations were prepared via. solution casting method. The thermal stability and ionic conductivity of PVA–KOH solid polymer electrolyte ( A) were improved by the partial substitution of KOH with zinc salts. Among the two salts, zinc triflate was found to improve both the physical as well as electrochemical properties of the PVA–KOH films more significantly than zinc acetate. An attempt to optimize the ratio of various components of polymer electrolytes, viz., polymer: KOH: zinc salt was also made, based on the dimensional stability and ionic conductivity values. Finally, the select category polymer film containing PVA–KOH–zinc triflate ( C) in an optimum ratio of 40:35:25 was deployed in coin cell fabrication and subjected to charge–discharge studies with a view to demonstrate the possible electrochemical reversibility characteristics. Based on the encouraging results obtained from the cycling study, C type films [PVA–KOH–zinc triflate] qualify themselves as potential polymer electrolytes for use in rechargeable Zn/AgO polymer batteries. [ABSTRACT FROM AUTHOR]

Perovskites have stood out as excellent photoactive materials with high efficiencies and stabilities, achieved via cation mixing techniques. Overcoming challenges to the stabilization of Perovskite solar cells calls for the development of design principles of large cation incorporation in halide perovskite to accelerate the discovery of optimal stable compositions. Large fluorinated organic cations incorporation is an attractive method for enhancing the intrinsic stability of halide perovskites due to their high dipole moment and moisture-resistant nature. However, a fluorinated cation has a larger ionic size than its non-fluorinated counterpart, falling within the upper boundary of the mixed-cation incorporation. Here, we report on the intrinsic stability of mixed Methylammonium (MA) lead halides at different concentrations of large cation incorporation, namely, ehtylammonium (EA; [CH3CH2NH3]+) and 2-fluoroethylammonium (FEA; [CH2FCH2NH3]+). Density functional theory (DFT) calculations of the enthalpy of the mixing and analysis of the perovskite structural features enable us to narrow down the compositional search domain for EA and FEA cations around concentrations that preserve the perovskite structure while pointing towards the maximal stability. This work paves the way to developing design principles of a large cation mixture guided by data analysis of DFT data. Finally, we present the automated search of the minimum enthalpy of mixing by implementing Bayesian optimization over the compositional search domain. We introduce and validate an automated workflow designed to accelerate the compositional search, enabling researchers to cut down the computational expense and bias to search for optimal compositions. [ABSTRACT FROM AUTHOR]

• Counter to our understanding, K 2 O and SrO increase the %B3 (at the same mol%) within the networks examined. Based on the coefficients associated with regression analysis both compounds exhibit a similar influence on the %B3 in the range from 0-31 mol%. • SrO has the largest positive coefficient in respect of increasing T g , suggesting that it plays a cross-linking role in the network. • Each of the 16 borate glasses modified with K 2 O and SrO did not exhibit any property changes following sterilization, making them suitable for various biomedical applications where soluble compounds are required. Sixteen borate glass compositions, modified with K 2 O and SrO, were established using a design of mixtures approach and were subjected to chemical and physical characterization (11B MAS NMR, density, and glass transition temperature (T g)). The analysis intended to establish the influence of K 2 O and SrO on the composition-structure-property relationships for borate glass networks. The effects of γ-radiation on the glass networks were also examined to determine the impact that sterilization may have on the glass properties. Structural analysis showed that both K 2 O and SrO influenced the fraction of three- and four-fold coordinated boron groups independent of the cation. Thermal analysis of the glasses revealed that SrO significantly increases the glass transition temperature while both SrO and K 2 O have comparable impacts on glass stability. These data suggest that Sr2+ cations cross-link the networks. Contrastingly, K+ appears to stabilize B4 structures. All sixteen compositions retained their chemical and physical characteristics following sterilization. [ABSTRACT FROM AUTHOR]

Phase pure Al-rich CHA(1.6–2.0) was prepared both from seed-assisted and non-seeded gel routes. Two different gel composition spaces were explored and both cation composition and the addition of seeds had a large effect on the product phase. A working hypothesis that guided the initial synthesis work is that the product phase and SAR is a strong function of the SiO 2 solubility for the given gel system and addition of a seed would nucleate a CHA phase. Adsorption studies on pure and mixed alkali/alkaline earth CHA(2.0) showed homogeneous isosteric heats and low N 2 Henry's constants for the pure Na and Li forms as well as Ca 2 Li 8 CHA(2.0); whereas a heterogenous heat and significant increase in Henry's constant were observed for higher Ca loadings in this mixed Ca/Li system. This behavior strongly suggests that in the dehydrated form, <2Ca/uc site inside the hexagonal prism of CHA, inaccessible to N 2. This work shows the specific cation content of the phase pure, Al-rich CHA can be tailored to exhibit highly effective adsorbents for removing N 2 from N 2 -containg streams. Image 1 • Narrow phase space for CHA formation enabled with seeding and/or K+. • Seed morphology affects crystallization rates. • Ca2+ is inaccessible to adsorbate molecules in Ca 2 Li 8 CHA(2.0). [ABSTRACT FROM AUTHOR]

• RCP-BTT random copolymer is synthesized by linking of PhC 8 TPD with BDT and FTT unit. • Dopant-free RCP-BTT shows deeper HOMO energy level than parent PTB7 & spiro-OMeTAD. • The dopant-free RCP-BTT shows enhanced V oc and FF than PTB7 and spiro-OMeTAD. • RCP-BTT with dopant delivered higher efficiency of 14.57% than PTB7. Hole transport materials (HTMs) with different hole extraction abilities play an important role in dictating the efficiency of the perovskite solar cells (PSCs). Besides, employing a donor acceptor (D-A) random copolymer HTM to bring out deeper HOMO energy level is highly beneficial to the hole extraction and durability of PSCs. In this context, a highly soluble D-A based random copolymeric benzodithiophene-thienopyrroledione-thienothiophene derivatives (RCP-BTT) HTM has been derived from the backbone structure of Poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7). The synthesized dopant-free RCP-BTT HTM shows a deeper HOMO energy level (−5.28 eV) due to its high compatibility than PTB7 level (−5.15 eV) based on perovskite energy level. Gradient band alignment of RCP-BTT has provided efficient hole extraction in the PSCs made of Cs-containing triple cation perovskite as absorber resulting in the efficient photovoltaic performance of RCP-BTT. The RCP-BTT with dopant shows significantly increased V oc (1.09 V) with respect to that of parent PTB7 (V oc of 1.06 V), resulting in an enhanced efficiency of 14.57% than that of PTB7 (12.02%). On the whole, the improvement in photovoltaic performance of PSC based on the polymeric RCP-BTT HTM is attributable to its deeper HOMO energy level and exceptional hole extraction ability. [ABSTRACT FROM AUTHOR]

The presence of surface and grain boundary defects in organic–inorganic halide perovskite films can be detrimental to both the performance and operational stability of perovskite solar cells (PSCs). Here, the effect of chloride additives is studied on the bulk and surface defects of the mixed cation and halide PSCs. It is found that using an antisolvent technique, the perovskite film is divided into two layers, i.e., a bottom layer with large grains and a thin capping layer with small grains. The addition of formamidinium chloride (FACl) into the precursor solution removes the small‐grained perovskite capping layer and suppresses the formation of bulk and surface defects, providing a perovskite film with enhanced crystallinity and large grain size of over 1 µm. Time‐resolved photoluminescence measurements show longer lifetimes for perovskite films modified by FACl and subsequently passivated by 1‐adamantylamine hydrochloride as compared to the reference sample. Impedance spectroscopy measurements show that these treatments reduce the recombination in the PSCs, leading to a champion device with power conversion efficiency (PCE) of 21.2%, an open circuit voltage of 1152 mV and negligible hysteresis. The Cl treated PSC also shows improved operational stability with only 12% PCE loss after 700 h under continuous illumination. [ABSTRACT FROM AUTHOR]

We study the thermal stability in air of the mixed cation organic-inorganic lead halide perovskites Cs 0.17 FA 0.83 Pb(I 0.83 Br 0.17 ) 3 and Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 . For the latter compound, containing both MA + and FA + ions, thermal decomposition of the perovskite phase was observed to occur in two stages. The first stage of decomposition occurs at a faster rate compared to the second stage and is only observed at relatively low temperatures (T < 150 °C). For the second stage, we find that both decomposition rate and the activation energy have similar values for Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 and Cs 0.17 FA 0.83 Pb(I 0.83 Br 0.17 ) 3 , which suggests that the first stage mainly involves reaction of MA + and the second stage mainly FA + .

Mixed anion/cation perovskites absorber has been recently implemented to construct highly efficient single junction solar cells and tandem devices. However, considerable efforts are still required to map the composition-property relationship of the mixed perovskites absorber, which is essential to facilitate device design. Here we report the intensive exploration of mixed-cation perovskites in their compositional space with the assistance of a rational mixture design (MD) methods. Different from the previous linear search of the cation ratios, it is found that by employing the MD methods, the ternary composition can be tuned simultaneously following simplex lattice designs or simplex-centroid designs, which enable significantly reduced experiment/sampling size to unveil the composition-property relationship for mixed perovskite materials and to boost the resultant device efficiency. We illustrated the composition-property relationship of the mixed perovskites in multidimension and achieved an optimized power conversion efficiency of 20.99% in the corresponding device. Moreover, the method is demonstrated to be feasible to help adjust the bandgap through rational materials design, which can be further extended to other materials systems, not limited in polycrystalline perovskites films for photovoltaic applications only.

Novel organic-inorganic hybrid perovskite compounds composed of mixed A-site cation (Formamidinium and Cesium) and pseudohalides (SCN and I) ions are successfully synthesized. These new classes of hybrid perovskites photovoltaics exhibited remarkable power conversion efficiency of more than 16% with excellent stability against moisture in ambient environment and under low-light storage condition. The existence of SCN - ion inclusion is confirmed by secondary ion mass spectrometry and Fourier transform infrared spectroscopy. The SCN - -doped pseudohalide is advantageous for the formation of large perovskite grains, as well as the performance and stability of the device.