Search

Converting PbI2 residues into low‐dimensional perovskites through post‐treatment with ammonium‐based large cations can passivate 3D perovskites, thus has emerged as an effective strategy to improve the performance of perovskite solar cells (PSCs). Herein, a dramatically improved efficiency is demonstrated for PSCs based on a two‐step‐processed FAPbI3 perovskite via post‐treatment with formamidinium (FA)‐based benzamidine hydrochloride (PFACl), outperforming the commonly used methylamine (MA)‐based benzylamine hydrochloride (PMACl). With an in‐depth exploration of the crystal structures and morphology changes of the FAPbI3 perovskite upon the PFACl post‐treatment, the preferential formation of 1D rather than 2D structures on the 3D perovskite film is identified. In contrast to the 2D counterpart, the more energetically favorable 1D structure enables a more effective elimination of PbI2 residues. As a consequence, the PFACl‐induced 1D/3D perovskite film is endowed with smoother morphology, more uniform surface potential distribution, lower trap density, faster charge transfer, and better film stability than the PMACl‐induced 2D/3D perovskite and control films, demonstrating champion efficiencies of 24.9% for a small‐size PSC, 23.6% for a 1 cm2 large‐size PSC, and 21.2% for a 5 × 5 cm2 mini‐module, which is the highest among the perovskite solar mini‐modules using the two‐step deposition method. [ABSTRACT FROM AUTHOR]

Low‐temperature solution processing of the perovskite layer enables the fabrication of flexible devices. However, the performance of flexible perovskite solar cells (f‐PSCs) lags far behind their rigid counterpart in terms of efficiency and stability. Emerging evidence demonstrates that the quality of the buried interface between perovskite and transporting layer underneath is the key point. Herein, a class of novel halide substituted ammonium salts, i.e., n‐bromophenethylammonium (n‐Br‐PEAX, n = 2 or 4, X = Cl or Br) are designed and synthesized to modify the buried interface as well as the perovskite crystallization of f‐PSCs. It is found that the ammonium salt with rational design molecular structure can modify the crystallization speed of perovskite, leading to the formation of a compact and uniform morphology without nanovoids at the interface. As a result, the efficiency of f‐PSCs is improved from 15.4% to 20.2%. Moreover, the modified devices without encapsulation retain 86% of their initial performance after 1000 h of aging at ambient conditions and 87% after 290 h of continuous operation. [ABSTRACT FROM AUTHOR]

In this study, high quality CsxFA1−xPbIyBr3−y perovskite thin films were successfully fabricated by an evaporation/spray-coating hybrid deposition method. In this method, CsI and PbI2 were first deposited via thermal evaporation, and then FAI/FABr mixed solution was sprayed on the CsI/PbI2 substrate to form the CsxFA1−xPbIyBr3−y film. As confirmed by x-ray diffraction, scanning electron microscopy, and atomic force microscopy, a perovskite film with full surface coverage and small surface roughness was obtained. Then, the effect of interface modification materials on the performance of perovskite solar cells (PSCs) was investigated: the devices with the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) interlayer incorporated via vacuum evaporation deposition between SnO2 and perovskite showed remarkably higher performance than those with the C60 interlayer, which was attributed to enhanced charge extraction and reduced recombination at the SnO2/PCBM/perovskite interface. As a result, a high power conversion efficiency (PCE) of 18.21% was obtained for the 0.16 cm2 device. To the best of our knowledge, it is the highest efficiency of CsxFA1−xPbIyBr3−y based PSCs fabricated by the spray technique. Furthermore, we fabricated mini-modules with the size of 5 × 5 cm2 and achieved a PCE of 14.7%. [ABSTRACT FROM AUTHOR]

The electron transport layer (ETL) plays a crucial role for efficiency and stability of perovskite solar cells (PSCs). As a promising low‐temperature ETL, tin oxide still requires complicated surface chemical decoration or heat‐treatments to further passivate the defects and adjust band energy level to improve the optoelectronic performance of the device. Herein, a novel and efficient strategy is developed for the solution prepared annealing‐free SnO2 ETL for PSCs. Through simple electrochemical regulation, the elemental composition, valence ratio of Sn, concentration of oxygen vacancies, hydroxyl groups, and dopant ions are precisely modified with the optimized the energy band, reduce the defect density, and enhance high carrier transport for PSCs. Thus, an increase of power conversion efficiency (PCE) from 21.6% to 24.7% and a high VOC of 1.19 V is obtained. The modified devices maintain 95% of the initial PCE after 2000 h of storage, and 80% of the initial PCE after 900 h of aging in an atmospheric environment at 75 °C and RH 20 ± 5%. Moreover, the perovskite solar module based on the as made SnO2 achieve a high PCE of 21.3%. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) based on SnO2 electron transport layers have attracted extensive research due to their compelling photovoltaic performance. Herein, we presented an in situ passivation of SnO2 with low‐cost hydroxyacid potassium synergist during deposition to optimize the interface carrier extraction and transport for high power conversion efficiency (PCE) and stabilities of PSCs. The orbital overlap of the carboxyl oxygen with the Sn atom alongwith the homogenous nano‐particle deposition effectively suppresses the interfacial defects and releases the internal residual strains in the perovskite. Accordingly, a PCE of 24.91 % with a fill factor (FF) up to 0.852 is obtained for in situ passivated devices, which is one of the highest values for SnO2‐based PSCs. Moreover, the unencapsulated device maintained 80 % of its initial PCE at 80 °C over 600 h, 100 % PCE at ambient conditions for 1300 h, and 98 % after one week maximum power point tracking (MPPT) under continuous AM1.5G illumination. [ABSTRACT FROM AUTHOR]

Despite the rapid developments are achieved for perovskite solar cells (PSCs), the existence of various defects in the devices still limits the further enhancement of the power conversion efficiency (PCE) and the long‐term stability of devices. Herein, the efficient organic potassium salt (OPS) of para‐halogenated phenyl trifluoroborates is presented as the precursor additives to improve the performance of PSCs. Studies have shown that the 4‐chlorophenyltrifluoroborate potassium salt (4‐ClPTFBK) exhibits the most effective interaction with the perovskite lattice. Strong coordination between BF3−/halogen in anion and uncoordinated Pb2+/halide vacancies, along with the hydrogen bond between F in BF3− and H in FA+ are observed. Thus, due to the synergistic contribution of the potassium and anionic groups, the high‐quality perovskite film with large grain size and low defect density is achieved. As a result, the optimal devices show an enhanced efficiency of 24.50%, much higher than that of the control device (22.63%). Furthermore, the unencapsulated devices present remarkable thermal and long‐term stability, maintaining 86% of the initial PCE after thermal test at 80 °C for 1000 h and 95% after storage in the air for 2460 h. [ABSTRACT FROM AUTHOR]

Surface passivation with organic halide salts is a powerful strategy to enhance the performance of perovskite solar cells. However, the inevitable formed in‐plane favored two‐dimensional perovskite layers with low carrier mobility and high binding energy inhibit the interfacial charge transfer within the device. Herein, a bulky fluorinated phenmethylammonium salt is designed and synthesized to passivate the perovskite film without forming 2D perovskites. A strong interaction which is induced by an electron donation from passivation agent to perovskite not only reduces the defects at the top surface of the perovskite, but also suppresses the recombination reaction at the buried surface due to a permeation of the organic halide salt. Moreover, the results of time resolved photoluminescence and confocal microscopy images suggest that the interfacial charge transfer speed and uniformity are enhanced. As a result, the efficiency of a small‐area device increases from 20.7 ± 0.9% to 22.8 ± 0.4% (aperture: 0.16 cm2). Moreover, a stabilized efficiency of 18.0% (aperture: 10.0 cm2) is achieved for larger‐area modules with 6‐series connected sub‐cells. Equally important, the non‐encapsulated modules show significantly improved stability at ambient conditions (ISOS‐D‐1). These significant improvements provided by a simple and reproducible procedure can be readily adopted in other types of devices. [ABSTRACT FROM AUTHOR]

As an alternative of evaporated metal top electrode in perovskite solar cells, the transferred top electrode technique has the outstanding advantage of simple process. And in the case of carbon based transferred top electrode, the efficiency of corresponding perovskite devices can be higher than 20%. During the solid-to-solid electrode transferring process, it is essential to achieve effective contact and to avoid damage of bottom functional layers for an improved device performance. In this work, a sprayed graphite layer on conductive substrate is employed as transferred top electrode for perovskite solar cells. A simple mechanical polishing treatment is further adopted to modify the surface status of graphite layer. Compared with as sprayed graphite electrode, polished electrode shows better electrical property and optimized interface contact with hole-transporting layer. Thus, the average efficiency of perovskite device with mechanical modified electrode can significantly increase from 16.3% to 19.2%. [Display omitted] [ABSTRACT FROM AUTHOR]

The present work demonstrates a facile one-step process to fabricate thin films of amorphous titania nanowires on transparent conducting oxide substrates via hydrolysis of potassium titanium oxide oxalate in an aqueous solution at 90 °C. The resultant titania nanowire thin films (that have not undergone further annealing) are efficient electron transport layers in CH 3 NH 3 PbI 3 perovskite solar cells, yielding full sun solar-to-electricity conversion efficiencies of up to 14.67% and a stabilized efficiency of 14.00% under AM 1.5G one sun illumination, comparable to high temperature sintered TiO 2 counterparts. The high photovoltaic performance is attributed to the porous nanowire network that facilitates perovskite infiltration, its unique 1D geometry and excellent surface coverage for efficient electron transport, as well as suppressed charge recombination between FTO and perovskite. [ABSTRACT FROM AUTHOR]

Metal‐halide perovskite solar cells (PSCs) exhibit outstanding power conversion efficiencies (PCEs) when fabricated as mm‐sized devices, but creation of high‐performing large‐area modules that are stable on a sufficiently long timescale still presents a significant challenge. Herein, the quality of large‐area perovskite film is improved by using ionic liquid additives via forming a new Pb‐N bonding between the ionic liquid and Pb2+. This new bond can be modulated by a critical screening of the anion structure of the ionic liquid. The selected ionic liquid effectively reduces the defects of the perovskite films and markedly elongate their carrier lifetimes. As a result, a champion PCE of 24.4% for small‐area (0.148 cm2) devices and 20.4% for larger‐area (10.0 cm2) modules under AM 1.5G irradiation is achieved. More importantly, the modified devices retain 90% of their peak PCE after aging for 1900 h at 65 ± 5 °C (ISOS‐T‐1) and 80% after continuous light soaking for 750 h. The non‐encapsulated modules maintained 80% of their peak PCE after 1100 h of aging in the air with a relative humidity of 35 ± 5% and temperature of 25 ± 5 °C under dark (ISOS‐D‐1), showing great potential for future commercialization. [ABSTRACT FROM AUTHOR]

Upscaling efficient and stable perovskite layers is one of the most challenging issues in the commercialization of perovskite solar cells. Here, a lead halide–templated crystallization strategy is developed for printing formamidinium (FA)–cesium (Cs) lead triiodide perovskite films. High-quality large-area films are achieved through controlled nucleation and growth of a lead halide•N-methyl-2-pyrrolidone adduct that can react in situ with embedded FAI/CsI to directly form a-phase perovskite, sidestepping the phase transformation from d-phase. A nonencapsulated device with 23% efficiency and excellent long-term thermal stability (at 85°C) in ambient air (~80% efficiency retention after 500 hours) is achieved with further addition of potassium hexafluorophosphate. The slot die–printed minimodules achieve champion efficiencies of 20.42% (certified efficiency 19.3%) and 19.54% with an active area of 17.1 and 65.0 square centimeters, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] [ABSTRACT FROM AUTHOR]

• We investigated the stability of four type APbI 3 perovskite solar cells under thermal cycling conditions. • The FA 0.9 Cs 0.1 PbI 3 devices show best stability. • Phase transition of perovskite materials caused the devices degradation. In this research, we investigated the influence of phase transition in four standard perovskite materials on the device stability under thermal cycling (TC) condition, which is listed in International Electrotechnical Commission (IEC) stability tests criteria. The evolution of morphology, phase structure and charge carrier dynamics of four type perovskite materials throughout thermal cycling were analyzed. It was found that the cubic to tetragonal phase transition of MAPbI 3 caused the quick degradation of the device, the α to δ phase transition in FAPbI 3 and FA 0.6 MA 0.4 PbI 3 resulted in sustained efficiency loss, while the FA 0.9 Cs 0.1 PbI 3 was more stable compared to above three perovskites under the same test condition. The FA 0.9 Cs 0.1 PbI 3 device retained nearly 88% of its initial efficiency after 200 temperature cycles between −30 °C and 85 °C, which could be ascribed to its successful stabilization of perovskite structure. [ABSTRACT FROM AUTHOR]

Although high efficiencies have been achieved for perovskite solar cells (PSCs), stability issues are still the key barriers for commercial applications. Herein, we carry out a systematic doping of non-radiative alkaline metal ions (Cs, Rb, K, Na, Li) to perovskite, studying their effects on perovskite morphology, electrical stability and performance of PSCs. The hysteresis related stability issues are also investigated at different conditions, such as steady-state power output, aging, repeated voltage sweeping, varied pre-scan voltage bias, etc. It is found the hysteresis becomes much severer at different test conditions for the devices doped with small sized Li and Na. While the subsized Rb and K ions (compared to Cs) doping can significantly enhance the crystallinity of perovskite and reduce the hysteresis that is also more stable. The crystallization, morphologies, time-resolved photoluminescence, electrochemical impedance spectroscopy were conducted to investigate the properties of the doped perovskite films to understand the relationship between the film quality and device performance. With a proper combination of Cs, Rb, K ions doping in PSCs, a high PCE over 20% is achieved with an enhanced electrical stability. Moreover, an over 17% efficiency 7 × 7 cm2 perovskite solar cell module is realized by this strategy, with a certified PCE of 16.5% (aperture area of 20.78 cm2) without hysteresis. [ABSTRACT FROM AUTHOR]

• A series of green solvents are screened for processing large area perovskite films. • N-butyl alcohol demonstrates high uniformity than traditional anti-solvents. • Application of pre-dissolved organic salts in anti-solvent can modify film quality. • A high efficiency of 13.85% for 100 cm2 perovskite solar module is achieved. Organic-inorganic hybrid halide perovskite solar cells (PSCs) have shown the potential for the commercialization due to its high efficiency and low cost. How to scale up the module nowadays becomes a great challenge. Anti-solvent assisted crystallization is one of the most widely used methods to obtain pinhole-free homogeneous perovskite films owing to its advantage of low cost and simple process. The commonly used anti-solvents are toxic, such as chlorobenzene and toluene. Herein, we have made an effort to find a green solvent engineering by the anti-solvent bath to produce large area uniform perovskite films. Compared to the traditional solvent processed perovskite films, the films produced by n-butyl alcohol soaking exhibit smoother surface and superior performance. A moderate concentration of FAI/MABr has been added in the n-butyl alcohol solution to compensate for the loss of FAI/MABr during the soaking step. By this means, it alleviates the phenomenon of cracks on the perovskite surface, which exhibited a champion efficiency of 17.67% for PSCs with small area of 0.16 cm2 and a PCE of 13.85% for 10 cm × 10 cm perovskite solar modules. [ABSTRACT FROM AUTHOR]

• The SnO 2 films are fabricated by magnetron sputtering at room-temperature. • The PSC based on sputtered SnO 2 under Ar:O 2 = 2:3 show higher V oc and PCE. • The working gas ratio, film thickness, annealing temperature are discussed. • The PSC based on the sputtered SnO 2 ETL show a champion efficiency of 18.20%. • The PSMs (aperture area: 16.07 cm2) show an efficiency of 14.71%. Hybrid perovskite solar cells (PSC) have gained stupendous achievement in single/tandem solar cell, semitransparent solar cell and flexible devices. Aiming for potential commercialization of perovskite photovoltaic technology, up scalable processing is crucial for all function layers in PSC. Herein we present a study on room temperature magnetron sputtering of tin oxide electron transporting layer (ETL) and apply it in a large area PSC for low cost and continues manufacturing. The SnO 2 sputtering targets with varied oxygen and deposition models are used. Specifically, the working gas ratio of Ar/O 2 during the radio frequency sputtering process plays a crucial role to obtain optimized SnO 2 film. The sputtered SnO 2 films demonstrate similar morphological and crystalline properties, but significant varied defect states and carrier transportation roles in the PSC devices. With further modification of thickness of SnO 2 , the PSCs based on sputtered SnO 2 ETL shows a champion efficiency of 18.20% in small area and an efficiency of 14.71% in sub-module with an aperture area of 16.07 cm2, which is the highest efficiency of perovskite sub module with sputtered ETLs. [ABSTRACT FROM AUTHOR]

A facile and effective method to simultaneously reduce the interfacial defects and enhance the charge transfer via modification of SnO 2 by potassium xanthate is used to fabricate efficient large-area (active area: 48.0 cm2) perovskite solar modules. [Display omitted] • Stabilized efficiency of 18.8 % for large-area (48.0 cm2) modules is achieved. • Potassium xanthate can simultaneously bind with perovksite and SnO 2. • The stability of the modules is substantially improved after the modification. Tin oxide (SnO 2) has been demonstrated as a promising electron transport material for high efficiency perovskite solar cells (PSCs) that made entirely via solution processing at low temperature (<200 °C). However, non-radiative recombination at SnO 2 |perovskite interface lead to a large voltage loss and performance variation. Herein, we present a facile and effective method to simultaneously reduce the interfacial defects and enhance the charge transfer via modification of SnO 2 by hypervalent potassium xanthate. The presence of Lewis acidic centers of the sulfur ligands, gives rise to a strong hypervalent interactions with both Pb2+ on the perovskite and Sn4+ on the SnO 2 surface, which accelerates the interfacial charge transfer and suppresses the recombination reaction. As a result, solar cells with a power conversion efficiency (PCE) of 23.4 % with negligible hysteresis are fabricated in light of significantly increased voltage in comparison with the relevant control. Moreover, a stabilized efficiency of 18.8 % for large-area (active area: 48.0 cm2) perovskite solar modules is achieved. The modules retain 90 % of their initial performance after aging at ambient for 600 h, which is substantially improved in comparison with the modules based on pristine SnO 2. [ABSTRACT FROM AUTHOR]

This work draws attention to environmental influence to function layers interfaces and the band alignment optimization of organic-inorganic metal halide planar perovskite solar cell (PSC), demonstrating an effective route to enhance the PSC photovoltaic conversion efficiency (PCE) and stability. The PCE of the PSC presents a sensitive correlation with the relative humidity (RH) during the electron transport layer (ETL) preparation. Through optimizing the RH condition, the PSCs show outstanding performances using sol-gel TiO 2 ETL prepared under 55 RH%. Moreover, we systematically investigate the Zr doping effect in the TiO 2 ink with a variation of Zr molar percentages from 0% to 7.5%. A high PCE of 15.06% with a good fill factor of 0.76 is obtained at 2 mol% Zr doping, in contrast to 12.25% of the undoped device. The Mott-Schottky analysis reveals that the elevated open-circuit voltage ( Voc ) is attributed to the upshifting of flat band potential of TiO 2 from −4.15 eV to −4.02 eV (vs. vacuum) after doping. Notably, the as-made cell shows low hysteresis and elevated stability with only 15% degradation of PCE (35% for PSC with pyrolyzed TiO 2 ) after 550 h/14 RH% ageing without encapsulation. [ABSTRACT FROM AUTHOR]

The process of our new strategy combining thermal evaporation and inkjet printing to fabricate high efficiency PSCs. [Display omitted] • · A new strategy was created that combined thermal evaporation and inkjet printing in the preparation of perovskite films. • · Solvent engineering in the control of perovskite film quality. • · Inkjet-printed methylammonium-free perovskite solar cell with a PCE exceeding 18% was firstly achieved. Inkjet printing is a sterling technique in the fabrication of large-scale perovskite solar cells (PSCs). Whereas, to obtain high quality perovskite films remains challenging because of the control of the drying of droplets. In this work, FAI is totally dissolved in n-Butanol and isopropanol (IPA) to react with PbI 2 /CsBr films. The addition of n-Butanol prolongs the drying time and inhibits the contact line pinning. Accordingly, the inkjet-printed Cs x FA 1-x Pb(I y Br 1-y) 3 perovskite films show great uniformity with large grain size. We ultimately achieve a champion device with a power conversion efficiency (PCE) of 18.26 % (0.15 cm2). [ABSTRACT FROM AUTHOR]

• The annealing process commonly used for fabricating wide bandgap perovskites generates massive defects due to the loss of bromide; • Br-complementation for wide bandgap perovskites is realized via surface treatment with PTABr; • Efficient large-area solar modules (10 cm2) based on wide bandgap perovskites is achieved. Wide bandgap metal-halide perovskites are promising photoactive materials to pair with silicon in tandem solar cells to achieve power conversion efficiency (PCE) higher than 30% at low cost. In this work, we found that massive defects are generated in wide bandgap perovskites due to the release of bromide under mild annealing (100 °C), which restrains the open-circuit voltage and thus the performance of solar cells. We report a bromide complementation strategy for wide bandgap perovskites via surface treatment with trimethylphenylammonium bromide (PTABr). As a result, significantly reduced charge recombination and elongated carrier lifetime are achieved, which improves both efficiency and stability of solar cells. A champion PCE of 17.0% for large-area (5 cm × 5 cm) modules with an active area of 10 cm2 is achieved, which is one of the best performance of perovskite solar modules based on wide bandgap perovskites. The solar cells and modules show enhanced stability under the stress of moisture, illumination and heat. Moreover, we achieve a PCE of 25.0% with four-terminal perovskite/silicon tandem solar cells. These results suggest that bromide complementation is a promising way in obtaining high efficiency and large-area perovskite/Si tandem solar cells with good stability. [ABSTRACT FROM AUTHOR]

Inorganic p-type NiO x was considered as an idea hole-transport layer (HTL) for perovskite solar cells due to its good transmittance in visible region and outstanding chemical stability. The p-type behavior of NiO x is mainly derived from its nonstoichiometric nature and determined by the Ni cation deficiency. Thus, the synthesizing methods play an important role to the electronic properties of NiO x films. And for most of the inverted PSCs with NiO x HTL, the hole-extraction efficiency was limited by the unmatched valence band and too much surface defects of NiO x , causing poor performance of the device. To date, solution-based synthesizing methods and surface treatments were widely used for achieving high efficiencies of the PSCs. But the vacuum-based synthesizing methods and surface treatments are rarely reported. Herein, we developed a facile plasma post-treatment for the electron-beam evaporated NiO x to regulate its Ni3+/Ni2+ ratio and improve its electronic performance. By using O 2 plasma treatment, we successfully enhanced the conductivity of the NiO x and optimized the charge-extraction capability. As a result, the all-vacuum deposited PSCs based on the O 2 plasma-treated NiO x HTL achieved a champion PCE of 17.84%. This facile approach is expected to be further developed for fabricating high-efficiency PSCs on textured silicon solar cell. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel ionic liquid namely BMPIP-TFSI was used as dopant to replace Li-TFSI. • The device based on ionic liquid dopant has a best PCE of 23.01%. • The device based on ionic liquid retaining 85% of its initial efficiency after 500 h stored under humid environment. Regarded as one of the best hole transporting material (HTM) for perovskite solar cells, 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) has suffered from instability induced by Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) hygroscopicity and aggregation. Herein, we replace Li-TFSI with the hydrophobic ionic liquid (IL) 1-Butyl-1-methylpiperidinium bis(trifluoromethyl sulfonyl)imide (BMPIP-TFSI). The BMPIP-TFSI functions as a p -type dopant in the spiro-OMeTAD, increasing the hole mobility, promoting the conductivity and enhancing the moisture-resistance of HTM. The corresponding perovskite solar cells achieve a champion power conversion efficiency exceeding 23%. Furthermore, the un-encapsulated devices show enhanced stability under humid environment, retaining 85% of its initial efficiency after 500 h. [ABSTRACT FROM AUTHOR]

Abstract: Oxygen plasma treatment of TiO2 films has been used to improve the efficiency of dye sensitized solar cells. Both a commercial TiO2 sample and a TiO2 thin film synthesized by a sol-gel technique were treated using a custom built inductively coupled plasma apparatus. X-ray photoelectron spectroscopy revealed that oxygen-plasma treatment increased the number of oxygen functional groups (hydroxyl groups) and introduced some Ti3+ species on the surface of TiO2. A sample solar cell with plasma treated TiO2 showed an overall solar-to-electricity conversion efficiency of 4.3%, about a 13% increase over untreated TiO2. The photon conversion efficiency for the plasma treated TiO2 was 34% higher than untreated TiO2. This enhanced cell-performance is partly due to increased dye adsorption from an increase in surface oxygen functional groups and also may be partly due to Ti3+ states on the surface of TiO2. [Copyright &y& Elsevier]

[Display omitted] • A batch production route is established for large-area, uniform SnO 2 ETLs film by chemical bath deposition. • The mercaptosuccinic acid is applied on the SnO 2 surface modification for energy band alignment and defects passivation. • A PCE variance (V a) with the as-made SnO 2 is 0.073, comparing to that of control sample of V a at 2.833. • A high efficiency of 22.54% was obtained for the FA-based perovskite device. Chemical bath deposited tin oxide film (CBD SnO 2) has been demonstrated as an amazing electron transporting layer for high photoconversion efficiency (PCE) hybrid perovskite solar cells (PSCs) over 25 %. The current CBD process is normally studied for small area devices. A rapid batch production of large-area CBD SnO 2 film with high and uniform performance is essential for potential upscaling of perovskite solar module. Herein, we carried out a modified batch CBD process, a double chemical bath deposition (DC), for batch fabrication of large-area (400 cm2) SnO 2 films and realized a homogenized PCE with a variance (V a) of 0.127, comparing to that of control sample of V a at 2.833. We further introduced mercaptosuccinic acid (MSA) at the interface of SnO 2 /perovskite for convenient energy band alignment and defects passivation, which significantly improved the PCE , stability and homogeneity of the devices. As a result, the mix-cation planar PSCs reaches 21.24% with further reduced V a of 0.073. A high efficiency of 22.54% was obtained for the narrow band gap FA-based perovskite device. These results suggest high potential of this modified CBD route for large area and high efficiency perovskite module preparation. [ABSTRACT FROM AUTHOR]

• Inspired from gilding decoration, a pressing transfer top electrode was developed. • Au electrode were prepared onto perovskite solar cells without vacuum or solvent. • 17.14% efficiency was obtained in perovskite solar cells with Au-transfer electrode. As a developing photovoltaic technology, perovskite solar cells evolve rapidly in materials and processing methods, especially for perovskite absorbers and charge selected layers. However, the evaporated top metal electrode in high performance devices changes little and may be a bottleneck for the cost reduction and large area fabrication. Here, a pressing transfer method is developed to prepare metal top electrode. Inspired from gilding decoration, Au layer can be deposited as top electrode and yield an efficiency of 17.14%. The decent performance and suitability for large-scale manufacturing reveals promising application of this transfer method based top electrode. [ABSTRACT FROM AUTHOR]

Compared with traditional rigid perovskite solar cells fabricated on glass, flexible perovskite solar cells have a wider range of applications due to their lightweight and bendability, which have attracted great attention. Besides, carbon materials have shown some advantages of abundance, long-term stability and appropriate energy level as top electrode in perovskite solar cells. However, the reports of flexible devices based on carbon electrode are quite rare for the mismatch between the configuration of flexible perovskite solar cells and common carbon electrode techniques. Here, we introduce carbon film electrode into flexible perovskite solar cells for the first time. A new composite carbon film electrode is prepared on a highly conductive and flexible substrate of conductive cloth. Considerable PCEs of 15.37% and 14.05% have been obtained in small area (0.1 cm2) and large area (1 cm2) carbon based flexible devices, respectively. The comparable performance with standard Au electrode device, enhanced stability and suitability for roll-to-roll manufacturing reveals promising application of this low-cost composite carbon electrode. • Carbon film electrodes were introduced into flexible perovskite solar cells. • Efficiency of carbon based rigid perovskite solar cells reached 19.36%. • 15.37% and 14.05% were obtained in 0.1 cm2 and 1 cm2 flexible devices respectively. [ABSTRACT FROM AUTHOR]

• A hydrophobic organic agent is used as a dual-function passivator for perovskites. • The treated device improves the PCE from 19.25% to 20.56%. • The treated device maintains 84% of the initial PCE after 1300 h under 65–75% RH. Organic and inorganic metal halide perovskite solar cells (PSCs) with an outstanding performance of low-cost manufacturing and low-temperature solution processing, have been regarded as the next-generation photovoltaic technology. However, the solution processed perovskite films usually have abundant defects, especially at the grain boundaries and surfaces, causing carrier recombination, hysteresis, and degradation. Herein, 4-(trifluoromethyl)benzylamine (TFMBA) is deposited on the surface of perovskites to form an ultrathin hydrophobic organic molecular layer, passivating the interfacial imperfections. By optimizing the post-treatment conditions, a remarkable power conversion efficiency (PCE) of 20.56% is realized based on Cs 0.05 (FA 0.85 MA 0.15) 0.95 Pb(I 0.85 Br 0.15) 3 perovskite. Impressively, the passivated ultrathin organic molecular layer effectively prohibits the penetration of moisture, resulting in unsealed PSCs retaining 84% of the original PCE after aged 1300 h at 65%−75% relative humidity (RH). SEM and XRD confirm that TFMBA can effectively passivate defects on the surface and grain boundaries, thereby prevent the perovskites from the irreversible decomposition with the immersion of moisture. This suggests that the TFMBA post-treatment has great potential in obtaining high-quality and stable perovskite films. [ABSTRACT FROM AUTHOR]

Carbon electrode-based perovskite solar cells have shown some advantages in materials cost and long term stability compared to the metal electrode-based devices. Among all the reported carbon electrode techniques, self-adhesive carbon film electrode via press transfer process can achieve high PCE comparable with the Au electrode device in small area perovskite solar cells (∼ 0.1 cm2). Herein, we further promote the carbon film electrode to match the practical square-centimeter scale device. Pre-assembled with highly conductive substrates as graphite paper or aluminum foil, the double layered composite carbon electrode can significantly reduce the series resistance, thus retaining the high photoelectric performance of large area device (1 cm2). Especially with the graphite paper/carbon film electrode, a highest PCE of 17.02% was obtained, which achieved 92% of the PCE of 18.56% in small device. The soft and compressible nature can be the superiority of graphite paper as conductive substrate in carbon film based electrode compared with aluminum foil. [ABSTRACT FROM AUTHOR]

The α-phase formamidinium lead tri-iodide (α-FAPbI 3 ) has become the most promising photovoltaic absorber for perovskite solar cells (PSCs) due to its outstanding semiconductor properties and astonishing high efficiency. However, the incomplete crystallization and phase transition of α-FAPbI 3 substantially undermine the performance and stability of PSCs. In this work, a series of the protic amine carboxylic acid ion liquids are introduced as the precursor additives to efficiently regulate the crystal growth and phase transition processes of α-FAPbI 3 . The MA 2 Pb 3 I 8 ·2DMSO phase is inhibited in annealing process, which remarkably optimizes the phase transition process of α-FAPbI 3 . It is noted that the functional groups of carboxyl and ammonium passivate the undercoordinated lead ions, halide vacancies, and organic vacancies, eliminating the deleterious nonradiative recombination. Consequently, the small-area devices incorporated with 2% methylammonium butyrate (MAB) and 1.5% n-butylammonium formate (BAFa) in perovskite show champion efficiencies of 25.10% and 24.52%, respectively. Furthermore, the large-area modules (5 cm × 5 cm) achieve PCEs of 21.26% and 19.27% for MAB and BAFa additives, indicating the great potential for commercializing large-area PSCs., (© 2023 Wiley-VCH GmbH.)

Perovskite solar cells (PSCs) show great promise for next-generation building-integrated photovoltaic (BIPV) applications because of their abundance of raw materials, adjustable transparency, and cost-effective printable processing. Owing to the complex perovskite nucleation and growth control, the fabrication of large-area perovskite films for high-performance printed PSCs is still under active investigation. Herein, the study proposes an intermediate-phase-transition-assisted one-step blade coating for an intrinsic transparent formamidinium lead bromide (FAPbBr 3 ) perovskite film. The intermediate complex optimizes the crystal growth path of FAPbBr 3 , resulting in a large-area, homogeneous, and dense absorber film. A champion efficiency of 10.86% with high open-circuit voltage up to 1.57 V is obtained with a simplified device architecture of glass/FTO/SnO 2 /FAPbBr 3 /carbon. Moreover, the unencapsulated devices maintain 90% of their initial power conversion efficiency after aging at 75 °C for 1000 h in ambient air, and 96% after maximum power point tracking for 500 h. The printed semitransparent PSCs, with average visible light transmittance over 45%, demonstrate high efficiencies for both small devices (8.6%) and 10 × 10 cm 2 modules (5.55%). Finally, the ability to customize the color, transparency, and thermal insulation properties of FAPbBr 3 PSCs makes them high prospects as multifunctional BIPVs., (© 2023 Wiley-VCH GmbH.)

Low cost is the eternal theme for any commercial production. Numerous efforts have been explored to realize low-cost, high-efficiency perovskite solar cells (PSCs), such as replacing the traditional spin-coating method with an economical printing strategy, simplifying the device structure, reducing the number of functional layers, etc . However, there are few reports on the use of low-cost precursors. Herein, we enable the low-cost fabrication of efficient PSCs based on a very cheaper low-purity PbI 2 via powder engineering. The low-purity PbI 2 is blended with formamidinium iodide followed by dissolving in a 2-methoxyethanol solvent, and then, the high-quality FAPbI 3 powders are formed via an inverse temperature crystallization process and solvent washing after several simple processes to reduce the impurities. As a result, the devices fabricated using the as-synthesized black powders based on the low-purity PbI 2 exhibit a champion power conversion efficiency (PCE) of 23.9% and retained ∼95% of the initial PCE after ∼400 h of storage in the conditions of 25 ± 5 °C and 25 ± 5 RH% without encapsulation. In addition, the upscaling fabrication of a 5 cm × 5 cm solar minimodule also demonstrates an impressive efficiency of 19.5%. Our findings demonstrate an economic strategy for the commercialization of PSCs from the perspective of low-cost production.

Flexible semitransparent perovskite solar cells (ST-PSCs) have great potential for use in high-density energy systems, such as building or vehicle integrated photovoltaics, considering the great features of PSC devices, including high performance, light weight, thin-film processability, and high near-infrared transmittance. Despite numerous efforts toward achieving efficiency and flexibility in ST-PSCs, the realization of high-performance and operational stability in ST-PSCs still require further development. Herein, we demonstrated the development of highly efficient, stable, and flexible ST-PSCs using polyimide-integrated graphene electrodes via a lamination-assisted bifacial cation exchange strategy. A high-quality perovskite layer was obtained through the cation exchange reaction using the lamination process, and ST-PSCs with 15.1% efficiency were developed. The proposed ST-PSC device also demonstrated excellent operational stability, mechanical durability, and moisture stability owing to the chemically inert and mechanically robust graphene electrodes. This study provides an effective strategy for developing highly functional ST-perovskite optoelectronic devices with high-performance and long-term operational stability.

The inclusion of potassium in perovskite solar cells (PSCs) has been widely demonstrated to enhance the power conversion efficiency and eliminate the hysteresis effect. However, the effects of the locations K + cations on the charge-carrier dynamics remain unknown with respect to achieving a more delicate passivation design for perovskite interfaces and bulk films. Herein, we employ the combined electrical and ultrafast dynamics analysis for the perovskite film to distinguish the effects of bulk doping and interfacial passivation of the potassium cation. Transient absorption spectroscopy indicates an enhancement of charge-carrier diffusion for K + -doped PSCs (from 808 to 605 ps), and charge-carrier transfer is significantly promoted by K + interface passivation (from 12.34 to 1.23 ps) compared with that of the pristine sample. Importantly, K + doping can suppress the formation of wide bandgap perovskite phases (e.g., FAPbI 0.6 Br 2.4 and FAPbI 1.05 Br 1.95 ) that generate an energy barrier on the charge-carrier transport channel.

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted enormous research attention due to their high efficiency and low cost. However, most of the PSCs with high efficiencies still need expensive organic materials as their hole-transport layer (HTL). Obviously, the highly expensive materials go against the low-cost concept of advanced PSCs. In this regard, inorganic NiO x was considered as an idea HTL due to its good transmittance in the visible region and outstanding chemical stability. But for most of the PSCs with a NiO x HTL, the hole-extraction efficiency was limited by the unmatched valence band and too many surface defects of the NiO x layer, especially for the vacuum-deposited NiO x and perovskite. Herein, we developed a facile strategy to overcome this issue by using self-assembled glycine molecules to treat the NiO x surface. With glycine on the surface, the NiO x exhibited a deeper valence band maximum and a faster charge-extraction at the NiO x /perovskite interface. What's more, the vacuum-deposited perovskite showed a better crystallinity on the NiO x + glycine substrate. As a result, the PSCs with a glycine interfacial layer achieved a champion PCE of 17.96% with negligible hysteresis. This facile approach is expected to be further developed for fabricating high-efficiency PSCs on textured silicon solar cells., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The preparation of Cs y FA 1- y PbI x Br 3- x -based perovskite by ultrasonic spraying has valuable application in the preparation of tandem solar cells on textured substrates due to its excellent stability and the advantages of large-area uniform preparation from the spraying technology. However, the bandgap of perovskite prepared by spraying method is difficult to adjust, and perovskites with a wide bandgap have the issue of phase instability. Here, we improved the crystallinity of the perovskite by simply controlling the post-annealing temperature. The results show that perovskite film prepared by hybrid spray method has the best crystallinity and device performance at a post-annealing temperature of 170 °C. On this basis, the bandgap of perovskite was changed from 1.53 eV to 1.76 eV by controlling the ratio of the organic halogen precursor solution. When the bandgap is 1.57 eV, a perovskite solar cell with an efficiency of 18.31% is obtained., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

To accelerate the commercial application of organic-inorganic hybrid perovskite solar cells (PSCs), it is necessary to develop simple and low-cost methods to prepare pinhole-free large-area perovskite films with high quality. A one-step blade coating method is regarded as a scalable technique. It is demonstrated that with the addition of N , N '-dimethylpropyleneurea (DMPU) in an FA-dominated perovskite precursor, a large-area high-quality perovskite film can be obtained by blade coating, achieving improved photovoltaic performance, thermal stability, and storage stability. It is found that the strong interaction between DMPU and Pb 2+ ions is beneficial to delay the nucleation crystallization process, increase the size of crystal grains, and improve the crystallinity of the perovskite film. Planar n-i-p solar cells introducing DMPU exhibit power conversion efficiencies of 20.20% for 0.16 cm 2 devices and 17.71% for 5 × 5 cm 2 modules with an aperture area of 10 cm 2 . In addition, the devices without encapsulation placed at 50 °C for 500 h and with a relative humidity of 20 ± 5% for 1000 h still maintain efficiencies above 80 and 90%, respectively, showing outstanding stability.

It is extremely desirable to explore high-efficient, affordable and robust oxygen electrocatalysts toward rechargeable Zn-air batteries (ZABs). A 3D porous nitrogen-doped graphene encapsulated metallic Ni 3 Fe alloy nanoparticles aerogel (Ni 3 Fe-GA 1 ) was constructed through a facile hydrothermal assembly and calcination process. Benefiting from 3D porous configuration with great accessibility, high electrical conductivity, abundant active sites, optimal nitrogen content and strong electronic interactions at the Ni 3 Fe/N-doped graphene heterointerface, the obtained aerogel showed outstanding catalytic performance toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Specifically, it exhibited an overpotential of 239 mV to attain 10 mA cm -2 for OER, simultaneously providing a positive onset potential of 0.93 V within a half-wave potential of 0.8 V for ORR. Accordingly, when employed in the aqueous ZABs, Ni 3 Fe-GA 1 achieved higher power density and superior reversibility than Pt/C-IrO 2 catalyst, making it a potential candidate for rechargeable ZABs., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

All-inorganic CsPbBr 3 perovskite solar cells have triggered incredible interest owing to their superior stability, especially under high temperature conditions. Different from the organic-inorganic hybrid perovskites, inorganic CsPbBr 3 perovskite always need a high annealing temperature for the formation of a cubic phase. Generally, the higher temperature (over 300 °C) and longer annealing time will promote the growth of CsPbBr 3 , resulting in larger grain sizes and lower trap density in the crystals. However, CsPbBr 3 perovskite can also be damaged by excessive annealing temperature (∼350 °C) and time, since PbBr 2 only has a melting temperature close to 357 °C. To address this issue, herein, we developed a novel pressure-assisted annealing method to prevent the sublimation of PbBr 2 at high temperature. The CsPbBr 3 films were firstly deposited by sequential thermal evaporation, and then annealed at 335 °C in an alloy pressure vessel. By controlling the pressure of the vessel, we obtained CsPbBr 3 films with various morphologies. At normal atmospheric pressure, the as-prepared CsPbBr 3 film exhibited small grain sizes and was full of pinholes. With the increase of annealing pressure, the grain sizes of the film showed a significant increasing trend, and the pinholes gradually vanished. When the pressure value came to 10 MPa, compact and uniform CsPbBr 3 films with large grain sizes were obtained. Based on these films, CsPbBr 3 perovskite solar cells with FTO/compact-TiO 2 /CsPbBr 3 /carbon architecture achieved a champion power conversion efficiency of 7.22%., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Despite the impressive photovoltaic performance with a power conversion efficiency beyond 23%, perovskite solar cells (PSCs) suffer from poor long-term stability, failing by far the market requirements. Although many efforts have been made towards improving the stability of PSCs, the thermal stability of PSCs with CH 3 NH 3 PbI 3 as a perovskite and organic hole-transport material (HTM) remains a challenge. In this study, we employed the thermally stable (NH 2 ) 2 CHPbI 3 (FAPbI 3 ) as the light absorber for the carbon-based and HTM-free PSCs, which can be fabricated by screen printing. By introducing a certain amount of CsBr (10%) into PbI 2 , we obtained a phase-stable Cs x FA 1- x PbBr x I 3- x perovskite by a "two-step" method and improved the device power conversion efficiency from 10.81% to 14.14%. Moreover, the as-prepared PSCs with mixed-cation perovskite showed an excellent long-term stability under constant heat (85 °C) and thermal cycling (-30 °C to 85 °C) conditions. These thermally stable and fully-printable PSCs would be of great significance for the development of low-cost photovoltaics., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Tin oxide (SnO 2 ) is widely used as electron transport layer (ETL) material in perovskite solar cells (PSCs). Numerous synthesis methods for SnO 2 have been reported, but they all require a proper thermal treatment for the SnO 2 ETLs. Herein we present a simple method to synthesize SnO 2 nanoparticles (NPs) at room temperature. By using butyl acetate as a precipitator and a proper UV-Ozone treatment to remove Cl residuals, excellent SnO 2 ETLs were obtained without any thermal annealing. The highest power conversion efficiency (PCE) of the prepared PSCs was 19.22% for reverse scan (RS) and 18.79% for forward scan (FS). Furthermore, flexible PSCs were fabricated with high PCEs of 15.27%/14.74% (RS/FS). The low energy consuming SnO 2 ETLs therefore show great promise for the flexible PSCs' commercialization., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Perovskite solar cells (PSCs) have reached an impressive efficiency over 23%. One of its promising characteristics is the low-cost solution printability, especially for flexible solar cells. However, printing large area uniform electron transport layers on rough and soft plastic substrates without hysteresis is still a great challenge. Herein, we demonstrate slot-die printed high quality tin oxide films for high efficiency flexible PSCs. The inherent hysteresis induced by the tin oxide layer is suppressed using a universal potassium interfacial passivation strategy regardless of fabricating methods. Results show that the potassium cations, not the anions, facilitate the growth of perovskite grains, passivate the interface, and contribute to the enhanced efficiency and stability. The small size flexible PSCs achieve a high efficiency of 17.18% and large size (5 × 6 cm 2 ) flexible modules obtain an efficiency over 15%. This passivation strategy has shown great promise for pursuing high performance large area flexible PSCs.

The hysteretic phenomenon commonly exists in the J - V curves of perovskite solar cells with different structures, especially for carbon-based mesoscopic perovskite solar cells without hole-conductor (carbon-based PSCs). By adding moderate amounts of methylammonium chloride (MACl) into MAPbI 3 perovskite precursor, we found the J - V hysteresis of carbon-based PSCs could be significantly alleviated and the crystallinity of MAPbI 3 perovskite could also be influenced. With the increasing amount of MACl, MAPbI 3 perovskite showed better and better crystallinity until the MACl came to 0.45 M. The champion device with 0.45 M of additional MACl exhibited a preferable PCE of 14.27% for reverse-scan (RS) and 14.50% for forward-scan (FS), significantly higher than that of the pristine device (8.74% for RS and 4.80% for FS). What's more, the J - V hysteretic index of the device gradually decreased along with the increasing amount of MACl, and kept at low value even when the crystallinity of MAPbI 3 perovskite became poor. Through XRD and PL analysis, we demonstrated that the recombination rate of the accumulated charges at the perovskite/TiO 2 interface is the main reason for photocurrent hysteresis in carbon-based PSCs. High quality of perovskite crystals is an important contributing factor for high-performance PSCs with low hysteresis, but there is no necessary correlation between low hysteresis and good crystallinity. This research presents an effective way to fabricate carbon-based PSCs with low-hysteresis, and at the same time, provides evidence for investigating the origin of J - V hysteresis of PSCs., Competing Interests: There are no conflict to declare., (This journal is © The Royal Society of Chemistry.)

Low-temperature solution-processed SnO 2 as a promising electron-transport material for planar perovskite solar cells (PSCs) has attracted particular attention because of its outstanding properties such as high optical transparency or high electron mobility. However, low-temperature sol-gel processes used in the synthesis are inevitably affected by the humidity of the atmosphere, which results in a wide distribution in the performance of the prepared PSCs owing to the inability to control crystallinity and defects. Herein, a highly crystalline SnO 2 film is synthesized using a simple water bath post-treatment, which can remove the surface residuals of SnCl 4 on the SnO 2 films, which is beneficial for the interface charge transport from the perovskite to the SnO 2 electron-transport layer. An improved performance of the PSCs can be easily obtained applying this treatment, giving rise to a high power conversion efficiency (PCE) of 19.17 %, much higher than that of the pristine SnO 2 -based device (17.59 %). Most importantly, the reproducibility of the devices has been greatly improved, independent of the environmental humidity. Therefore, the enhanced crystallinity of SnO 2 has shown promise for future commercial PSC applications: 5 cm×5 cm PSC modules have achieved a PCE of 16.16 %., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cesium 5-aminovaleric acetate (NH 2 C 4 H 8 COOCs) was used to improve the intrinsic thermal stability of the methylammonium lead triiodide (MAPbI 3 ) perovskite. The corresponding carbon-based perovskite solar cells without encapsulation showed favourable stability at 100 °C for 500 h., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Large-area, pinhole-free CH 3 NH 3 PbI 3 perovskite thin films were successfully fabricated on 5 cm × 5 cm flexible indium tin oxide coated polyethylene naphthalate (ITO-PEN) substrates through a sequential evaporation/spin-coating deposition method in this research. The influence of the rate-controlled evaporation of PbI 2 films on the quality of the perovskite layer and the final performance of the planar-structured perovskite solar cells were investigated. An ultrafast evaporation rate of 20 Å s -1 was found to be most beneficial for the conversion of PbI 2 to CH 3 NH 3 PbI 3 perovskite. Based on this high-quality CH 3 NH 3 PbI 3 film, a resultant flexible perovskite solar sub-module (active area of 16 cm 2 ) with a power conversion efficiency of more than 8% and a 1.2 cm 2 flexible perovskite solar cell with a power conversion efficiency of 12.7% were obtained.

A complex titania nanostructure of monodisperse spiky mesoporous anatase beads composed of anatase nanocrystals with diameters of less than 15 nm in the core and much larger hollow-cone shaped spikes on the surface was fabricated using a facile solvothermal process in the presence of ammonia. This proceeded through a controllable phase transformation from an amorphous titania to a metastable amorphous titania/ammonium titanate core-shell structure then finally to anatase titania. The size of the spiky anatase nanostructures can be increased from approximately 55 × 100 nm to 160 × 410 nm (square edge × length) by increasing the ammonia concentration used in the solvothermal treatment step from 2.2 to 17.4 wt. %. Such hollow-cone shaped nanostructures, as revealed by HRTEM characterization, are single crystals elongated along the c axis of the tetragonal anatase titania. The resultant spiky titania beads have high surface areas of up to 112 m(2) g(-1) and pore diameters and pore volumes that vary depending on the ammonia concentration and solvothermal treatment time. The morphological evolution and crystallization process of the spiky titania beads was investigated using SEM and XRD techniques. A metastable amorphous titania/ammonium titanate core-shell structure evolved from the smooth amorphous precursor beads producing a "fluffy" titanate intermediate, on further heating the final spiky mesoporous titania beads were clearly observed. This titanate-phase-mediated approach allows control over the size of the nanocrystals in the core of the bead, as well as the anatase spikes on the surface, and thereby, tuning of the surface area and porosity of the resultant products. The spiky mesoporous titania beads have been used to prepare working electrodes for dye-sensitized solar cells achieving a solar to electric power conversion efficiency of 10.30 %, indicating their potential for application in the photovoltaic field. Such complex titania nanostructures would have a number of other possible applications, such as photocatalysis, lithium ion batteries, and catalysis., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Monodisperse mesoporous anatase titania beads with high surface areas and tunable pore size and grain diameter have been prepared through a combined sol-gel and solvothermal process in the presence of hexadecylamine (HDA) as a structure-directing agent. The monodispersity of the resultant titania beads, along with the spherical shape, can be controlled by varying the amount of structure-directing agent involved in the sol-gel process. The diameter of the titania beads is tunable from approximately 320 to 1150 nm by altering the hydrolysis and condensation rates of the titanium alkoxide. The crystallite size, specific surface area (from 89 to 120 m(2)/g), and pore size distribution (from 14 to 23 nm) of the resultant materials can be varied through a mild solvothermal treatment in the presence of varied amounts of ammonia. On the basis of the results of small-angle XRD, high-resolution SEM/TEM, and gas sorption characterization, a mechanism for the formation of the monodisperse precursor beads has been proposed to illustrate the role of HDA in determining the morphology and monodispersity during the sol-gel synthesis. The approach presented in this study demonstrates that simultaneous control of the physical properties, including specific surface area, mesoporosity, crystallinity, morphology, and monodispersity, of the titania materials can be achieved by a facile sol-gel synthesis and solvothermal process.