HONH3Cl optimized CH3NH3PbI3 films for improving performance of planar heterojunction perovskite solar cells via a one-step route.

Planar heterojunction perovskite solar cells (PHJ-PSCs) constructed with one-step precursor solution spin-coating deposition (OPSSD) usually give an extremely low performance mainly due to the poor morphology and low crystallinity of the perovskite films. In this work, by incorporating a suitable HONH3Cl additive in the perovskite precursor solution, a high quality perovskite film with improved morphology and crystallinity was obtained. The UV-vis measurement of the CH3NH3I solutions without and with HONH3Cl demonstrates that the improved quality of the perovskite film can be easily attributed to a combined effect of N2, I2, H2O and CH3NH3Cl originating from the oxidation of CH3NH3I triggered by the HONH3Cl additive, which can manipulate the crystallization process of the perovskite. Accordingly, the improved performance for the HONH3Cl-induced PHJ-PSCs can also be demonstrated. At the optimized molar ratio of 1 : 1 : 0.1 for PbI2 : CH3NH3I : HONH3Cl, the PHJ-PSCs exhibit an average power conversion efficiency (PCE) of 10.61 ± 0.51%, which is much higher than that of pristine 1 : 1 : 0 based cells without additive (7.21 ± 0.61%), and the best performing HONH3Cl-induced device can yield a PCE as high as 11.12% with a Jsc of 18.42 mA cm-2, Voc of 0.95 V and FF of 0.63. Introducing suitable HONH3Cl as an additive into the perovskite precursor solution is really an effective route to enhance the performance of the PHJ-PSCs via OPSSD.

A detailed study on the working mechanism of a heteropoly acid modified TiO2 photoanode for efficient dye-sensitized solar cells.

A novel heteropolyacid (HPA) K6SiW11O39Ni(H2O)·xH2O (SiW11Ni) modified TiO2 has been successfully synthesized and introduced into the photoanode of dye-sensitized solar cells (DSSCs). The performance of the cell with the HPA-modified photoanode (SiW11Ni/TiO2), mixed with P25 powder in the ratio of 2 : 8, is better than the cell with a pristine P25 photoanode. An increase of 31% in the photocurrent and 22% improvement in the conversion efficiency are obtained. The effect of the heteropolyacid was well studied by UV-vis spectroscopy, spectro-electrochemical spectroscopy, dark current, intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy, open-circuit voltage decay and electrochemical impedance spectroscopy. The results show that the interfacial layer modified by SiW11Ni can enhance the injection and transport of electrons, and then retard the recombination of electrons, which results in a longer electron lifetime. What's more, the introduction of SiW11Ni can simultaneously broaden the absorption in the visible region, eventually leading to an efficient increase in energy conversion efficiency.

All-Inorganic Perovskite Solar Cells: Defect Regulation and Emerging Applications in Extreme Environments.

All-inorganic perovskite solar cells (PSCs), such as CsPbX3, have garnered considerable attention recently, as they exhibit superior thermodynamic and optoelectronic stabilities compared to the organic-inorganic hybrid PSCs. However, the power conversion efficiency (PCE) of CsPbX3 PSCs is generally lower than that of organic-inorganic hybrid PSCs, as they contain higher defect densities at the interface and within the perovskite light-absorbing layers, resulting in higher non-radiative recombination and voltage loss. Consequently, defect regulation has been adopted as an important strategy to improve device performance and stability. This review aims to comprehensively summarize recent progresses on the defect regulation in CsPbX3 PSCs, as well as their cutting-edge applications in extreme scenarios. The underlying fundamental mechanisms leading to the defect formation in the crystal structure of CsPbX3 PSCs are firstly discussed, and an overview of literature-adopted defect regulation strategies in the context of interface, internal, and surface engineering is provided. Cutting-edge applications of CsPbX3 PSCs in extreme environments such as outer space and underwater situations are highlighted. Finally, a summary and outlook are presented on future directions for achieving higher efficiencies and superior stability in CsPbX3 PSCs.

Using highly water-stable wool keratin/CsPbBr3 nanocrystals as a portable amine-responsive fluorescent test strip for onsite visual detection of food freshness.

Perovskite nanocrystals (PNCs) have emerged as promising candidates for fluorescent probes owing to their outstanding photoelectric properties. However, the conventional CsPbBr3 (CPB) NCs are extremely unstable in water, which has seriously limited their sensing applications in water environment. Herein, we present a powerful ligand engineering strategy for fabricating highly water-stable CPB NCs by using a biopolymer of wool keratin (WK) as the passivator and the polyaryl polymethylene isocyanate (PAPI) as the cross-linking agent. In particular, WK with multi-functional groups can serve as a polydentate ligand to firmly passivate CPB NCs by the ligand exchange process in hot toluene; and then the addition of PAPI can further encapsulate CPB NCs by the crosslinking reaction between PAPI and WK. Consequently, the as-prepared CPB/WK-PAPI NCs can maintain âˆ¼ 80 % of their relative photoluminescence (PL) intensity after 60 days in water, and they still maintain âˆ¼ 40 % of their relative PL intensity even after 512 days in the same environment, which is one of the best water stabilities compared previously reported polymer passivation methods. As a proof-of their application, the portable CPB/WK-PAPI NCs-based test strips are further developed as a fluorescent nanoprobe for real-time and visual monitoring amines and food freshness. Among various amine analytes, the as-prepared test strips exhibit higher sensitivity towards conjugated amines, achieving a remarkable detection limit of 18.3 nM for pyrrole. Our research not only introduces an innovative strategy involving natural biopolymers to enhance the water stability of PNCs, but also highlights the promising potential of PNCs for visually and portably detecting amines and assessing food freshness.

Application of Perovskite Nanocrystals as Fluorescent Probes in the Detection of Agriculture- and Food-Related Hazardous Substances.

Halide perovskite nanocrystals (PNCs) are a new kind of luminescent material for fluorescent probes. Compared with traditional nanosized luminescent materials, PNCs have better optical properties, such as high fluorescence quantum yield, tunable band gap, low size dependence, narrow emission bandwidth, and so on. Therefore, they have broad application prospects as fluorescent probes in the detection of agriculture- and food-related hazardous substances. In this paper, the structure and basic properties of PNCs are briefly described. The water stabilization methods, such as polymer surface coating, ion doping, surface passivation, etc.; are summarized. The recent advances of PNCs such as fluorescent probes for detecting hazardous substances in the field of agricultural and food are reviewed, and the detection effect and mechanism are discussed and analyzed. Finally, the problems and solutions faced by PNCs as fluorescent probes in agriculture and food were summarized and prospected. It is expected to provide a reference for further application of PNCs as fluorescent probes in agriculture and food.

A Light/Pressure Bifunctional Electronic Skin Based on a Bilayer Structure of PEDOT:PSS-Coated Cellulose Paper/CsPbBr3 QDs Film.

With the continuous development of electronic skin (e-skin), multifunctional e-skin is approaching, and in some cases even surpassing, the capabilities of real human skin, which has garnered increasing attention. Especially, if e-skin processes eye's function, it will endow e-skins more powerful advantages, such as the vision reparation, enhanced security, improved adaptability and enhanced interactivity. Here, we first study the photodetector based on CsPbBr3 quantum dots film and the pressure sensor based on PEDOT: PSS-coated cellulose paper, respectively. On the base of these two kinds of sensors, a light/pressure bifunctional sensor was successfully fabricated. Finally, flexible bifunctional sensors were obtained by using a flexible interdigital electrode. They can simultaneously detect light and pressure stimulation. As e-skin, a high photosensitivity with a switching ratio of 168 under 405 nm light at a power of 40 mW/cm2 was obtained and they can also monitor human motions in the meantime. Our work showed that the strategy to introduce perovskite photodetectors into e-skins is feasible and may open a new way for the development of flexible multi-functional e-skin.

Electroluminescence of poly(N-vinylcarbazole) films: fluorescence, phosphorescence and electromers.

We have studied the electroluminescence (EL) properties of pure poly(N-vinylcarbazole) (PVK) films. Three types of light emission in the EL spectrum were observed, attributed to fluorescence, phosphorescence and electromers, respectively. The observation of electrophosphorescence from PVK films at room temperature is very meaningful, indicating that PVK can produce a large number of triplet excitons under an electric field at room temperature. Our results demonstrate clearly the reason why PVK is an excellent host material for phosphorescent polymer light-emitting diodes (PLEDs).

Enhanced Efficiency of Planar Heterojunction Perovskite Solar Cells by a Light Soaking Treatment on Tris(pentafluorophenyl)borane-Doped Poly(triarylamine) Solution.

This research used Lewis acid tris(pentafluorophenyl)borane (BCF) as a p-type dopant and a light soaking (LS) treatment to improve the conductivity of poly(triarylamine) (PTAA). Specifically, the conductivity of PTAA films was improved by two orders of magnitude using BCF as a p-type dopant, and the conductivity of BCF-doped PTAA films could be further improved by using the LS treatment on its solution. The working mechanism of the formation of frustrated Lewis pairs between BCF and PTAA was proposed to explain the BCF doping and LS treatment effects on the hole transport property of PTAA. When 5 min LS-PTAA films with 8 wt % BCF were used as the hole transport layer in p-i-n planar heterojunction perovskite solar cells, a maximum power conversion efficiency of 17.12% was achieved. This work provides a deep understanding of the enhancement of the conductivity of PTAA by the BCF doping and LS treatment. In addition, a convenient and quick LS method was explored to improve the conductivity of the PTAA hole transport material. Our findings may help in improving the hole transport properties of other organic photoelectric materials and devices.

Comparison Study of Wide Bandgap Polymer (PBDB-T) and Narrow Bandgap Polymer (PBDTTT-EFT) as Donor for Perylene Diimide Based Polymer Solar Cells.

Perylene diimide (PDI) derivatives as a kind of promising non-fullerene-based acceptor (NFA) have got rapid development. However, most of the relevant developmental work has focused on synthesizing novel PDI-based structures, and few paid attentions to the selection of the polymer donor in PDI-based solar cells. Wide bandgap polymer (PBDB-T) and narrow bandgap polymer (PBDTTT-EFT) are known as the most efficient polymer donors in polymer solar cells (PSCs). While PBDB-T is in favor with non-fullerene acceptors achieving power conversion efficiency (PCE) more than 12%, PBDTTT-EFT is one of the best electron donors with fullerene acceptors with PCE up to 10%. Despite the different absorption profiles, the working principle of these benchmark polymer donors with a same electron acceptor, specially PDI-based acceptors, was rarely compared. To this end, we used PBDB-T and PBDTTT-EFT as the electron donors, and 1,1'-bis(2-methoxyethoxyl)-7,7'-(2,5-thienyl) bis-PDI (Bis-PDI-T-EG) as the electron acceptor to fabricate PSCs, and systematically compared their differences in device performance, carrier mobility, recombination mechanism, and film morphology.

Improved Performance and Reproducibility of Perovskite Solar Cells by Well-Soluble Tris(pentafluorophenyl)borane as a p-Type Dopant.

In this work, well-soluble tris(pentafluorophenyl)borane (BCF) is introduced for the first time into 2,2',7,7'-tetrakis(N,N'-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) as a p-dopant. The conductivity of spiro-OMeTAD films is dramatically enhanced. When the BCF-doped spiro-OMeTAD film is used as a hole-transport layer (HTL) in perovskite solar cells (PSCs), nearly double increase in power conversion efficiency (PCE) is obtained compared to that of the PSCs based on a pristine spiro-OMeTAD HTL. By the introduction of lithium bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine into the BCF-doped spiro-OMeTAD film, the conductivity of spiro-OMeTAD film can be further enhanced, and an optimum PCE of 14.65% is obtained. In addition, the average efficiency of the device and the reproducibility of BCF-based PSCs are better than those of FK209-based PSCs. The working mechanism of the BCF doping effect on spiro-OMeTAD is studied in detail. The strong electron-accepting ability, excellent solubility in common organic solvents, and the low cost make BCF a very attractive p-type dopant for spiro-OMeTAD.

Keggin-Type PMo11V as a P-type Dopant for Enhancing the Efficiency and Reproducibility of Perovskite Solar Cells.

The conventional perovskite solar cells (PSCs) with 2,2',7,7'-tetrakis(N,N-dimethoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) as a hole transporting material commonly suffer from poor stability and reproducibility mainly due to the process of placing the devices in air and illumination for oxidizing the spiro-OMeTAD. Herein, Keggin-type polyoxometalates (POMs)-phosphovanadomolybdate (H4PMo11V·nH2O, denoted as PMo11V) is for the first time employed as a p-type dopant for promoting the oxidation of spiro-OMeTAD. Thereby, without illumination and air, the conductivity and hole extraction efficiency of the PMo11V doped spiro-OMeTAD with assistance of lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and 4-tert-butylpyridine (TBP) can be dramatically enhanced. On the basis of this strategy, the corresponding PSCs exhibit substantially improved photovoltaic performance and good reproducibility. The best performing device yields a power conversion efficiency (PCE) of 14.05%. This work indicates a great potential of polyoxometalates for further applications in solar cells and other optoelectronics devices.

SiW12 -TiO2 Mesoporous Layer for Enhanced Electron-Extraction Efficiency and Conductivity in Perovskite Solar Cells.

High quality electron-transport layer (ETL) with superior optical and electrical properties is an essential part in high efficient perovskite solar cells (PSCs). In this work, SiW12 -TiO2 mesoporous film is prepared by a facile one-step spin-coating deposition method and successfully applied as ETL in PSCs. Compared with pristine TiO2 -based PSC, the SiW12 -TiO2 -based one shows a remarkable enhanced power conversion efficiency (PCE) from 12.00 to 14.66 %, which is owed to the higher conductivity, electron-extraction efficiency, and well-matched energy level alignment of SiW12 -TiO2 film. Moreover, the SiW12 -TiO2 -based device also shows a good long-time stability in under ambient conditions. This work demonstrates that using polyoxometalates (POMs) to modify the metal-oxide semiconductors is an effective approach for further enhancing the performance of PSCs.

Nickel silicotungstate-decorated Pt photocathode as an efficient catalyst for triiodide reduction in dye-sensitized solar cells.

A new type of polyoxometalate material, K6SiW11O39Ni(H2O)·xH2O (denoted as SiW11Ni), was successfully synthesized and introduced to a dye-sensitized solar cell (DSSC) with modified traditional Pt as a novel composite counter electrode. The new counter electrode showed superior electrochemical catalytic activity for the reduction of I3- to I- in analysis utilizing a Tafel-polarization curve, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The DSSC assembled with the SiW11Ni/Pt photocathode exhibited an enhanced performance (7.03%) under the standard AM 1.5G illumination compared to the DSSC with a pristine Pt photocathode (6.65%). Furthermore, the DSSC based on the SiW11Ni/Pt photocathode had an increased light-harvesting efficiency and was very stable. The results demonstrate that SiW11Ni/Pt is an alternative and highly efficient counter electrode for dye-sensitized solar cells. Moreover, the facile design strategy is promising for fabricating efficient and inexpensive composite counter electrode catalysts for DSSCs.

Understanding the Light Soaking Effects in Inverted Organic Solar Cells Functionalized with Conjugated Macroelectrolyte Electron-Collecting Interlayers.

Three kinds of charged star-shaped conjugated macroelectrolytes, named as PhNBr, TPANBr, and TrNBr, are synthesized as electron-collecting interlayers for inverted polymer solar cells (i-PSCs). Based on these well-defined structured interlayer materials, the light soaking (LS) effect observed in i-PSCs was studied systematically and accurately. The general character of the LS effect is further verified by studying additional i-PSC devices functionalized with other common interlayers. The key-role of UV photons was confirmed by electrochemical impedance spectroscopy and electron-only devices. In addition, the ultraviolet photoelectron spectroscopy measurements indicate that the work function of the indium tin oxide (ITO)/interlayer cathode is significantly reduced after UV treatment. In these i-PSC devices the LS effect originates from the adsorbed oxygen on the ITO substrates when oxygen plasma is used; however, even a small amount of oxygen from the ambient is also enough for triggering the LS effect, albeit with a weaker intensity. Our results suggest that the effect of adsorbed oxygen on ITO needs to be considered with attention while preparing i-PSCs. This is an important finding that can aid the large-scale manufacturing of organic solar cells via printing technologies, which do not always ensure the full protection of the device electrode substrates from oxygen.

Well-defined star-shaped conjugated macroelectrolytes as efficient electron-collecting interlayer for inverted polymer solar cells.

A star-shaped monodisperse conjugated macroelectrolyte grafted with cationic side chains, TrNBr, was designed, synthesized, and utilized as efficient electron-collecting cathode interlayers for inverted polymer solar cells. A neutral one composed of identical star-shaped conjugated backbone, TrOH, was also investigated for comparison. The surface properties and the function as interfacial layers on modulating the work function of bottom electrode (indium tin oxide) were systematically studied. Both interfacial electron-selective materials show strongly thickness-dependent performance for inverted polymer solar cells, and the best performance could be achieved via optimizing the thickness with 2.4 nm of TrNBr and 8.7 nm of TrOH. Parallel investigations of optimized TrNBr and TrOH interlayer in inverted architecture with active blend layer of poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:ICBA) demonstrated a remarkable power conversion efficiency (PCE) enhancement (PCE of 4.88% for TrNBr and 4.74% for TrOH) in comparison with those of conventional noninverted devices using Ca/Al cathodes (3.94%) and inverted devices with sol-gel ZnO buffer layer (4.21%). In addition, the inverted devices using the TrNBr and TrOH interlayer exhibited improved device stability in contrast to conventional noninverted devices using Ca/Al cathodes.

Elucidating the impact of molecular packing and device architecture on the performance of nanostructured perylene diimide solar cells.

The performance of organic photovoltaic devices (OPV) with nanostructured polymer:perylene diimide (PDI) photoactive layers approaches the levels of the corresponding polymer:fullerene systems. Nevertheless, a coherent understanding of the difficulty for PDI-based OPV devices to deliver high power conversion efficiencies remains elusive. Here we perform a comparative study of a set of four different polymer:PDI OPV model systems. The different device performances observed are attributed to differences in the nanostructural motif of these composites, as determined by wide-angle X-ray scattering (WAXS) measurements. Long-range structural order in the PDI domain dictates (i) the stabilization energy and (ii) the concentration of the PDI excimers in the composites. The quenching of the PDI excimer photoluminescence (PL) is found to be insensitive to the former, but it depends on the latter. High PL quenching occurs for the low concentration of PDI excimers that are formed in PDI columns with a length comparable to the PDI excimer diffusion length. The stabilization of the PDI excimer state increases as the long-range order in the PDI domains improves. The structural order of the PDI domains primarily affects charge transport. Electron mobility reduces as the size of the PDI domain increases, suggesting that well-ordered PDI domains suffer from poor electronic connectivity. WAXS further reveals the presence of additional intermolecular PDI interactions, other than the direct face-to-face intermolecular coupling, that introduce a substantial energetic disorder in the polymer:PDI composites. Conventional device architectures with hole-collecting ITO/PEDOT:PSS bottom electrodes are compared with inverted device architectures bearing bottom electron-collecting electrodes of ITO/ZnO. In all cases the ZnO-functionalized devices surpass the performance of the conventional device analogues. X-ray photoelectron spectroscopy explains that in PEDOT: PSS-functionalized devices, the PDI component preferentially segregates closer to the hydrophilic PEDOT: PSS electrode, thus impeding the efficient charge extraction and limiting device photocurrent.

Effect of local and global structural order on the performance of perylene diimide excimeric solar cells.

Herein, we present a detailed study of the structure-function relationship in the organic photovoltaic (OPV) blend film composed of N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and the low energy gap copolymer of poly[4,8-bis-substituted-benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-4-substituted-thieno[3,4-b]thiophene-2,6-diyl] (PBDTTT-E-O). The hierarchical organization in the photoactive layers and in extruded fibers of PBDTTT-E-O:EP-PDI was studied by fluorescence optical microscopy, atomic force microscopy, and wide-angle X-ray scattering (WAXS). WAXS revealed a nanophase-separated structure where PBDTTT-E-O domains of 4.3 nm in size coexist with EP-PDI domains of 20 nm size. Thermal annealing results in an increase of the PBDTTT-E-O domains, but it does not affect the size of the EP-PDI domains. Only the length of the EP-PDI columns in each domain is increased by thermal treatment. The photophysical characterization of the PBDTTT-E-O:EP-PDI layers and the electrical characterization of the corresponding OPV and unipolar carrier devices were performed. The quenching of the EP-PDI excimer luminescence is correlated with the photocurrent generation efficiency of the OPV devices. At high annealing temperatures the EP-PDI columnar length becomes larger than the previously reported diffusion length of the PDI excimer, and fewer excimers dissociate at the EP-PDI/polymer interfaces, leading to reduced photocurrent generation. The charge transport properties of the PBDTTT-E-O:EP-PDI blend film were studied as a function of the active layer microstructure that was tuned by thermal treatment. Thermal processing increases electron mobility, but the poor connectivity of the EP-PDI domains keeps hole mobility six times higher. In respect to the as-spun OPV device, a 3-fold increase is found in the power conversion efficiency of the device annealed at 100 °C. The high surface roughness of the PBDTTT-E-O:EP-PDI photoactive layer impedes the efficient extraction of charges, and a thin and smooth perylene-3,4,9,10-tetracarboxylic bisbenzimidazole overlayer is required for increasing the device performance to a power conversion efficiency (PCE) ∼ 1.7%. The inversion in the polarity of the device contacts resulted in an inverted device with PCE ∼ 1.9%. We provide rational guidelines for the accurate tuning of the layer microstructure in PDI-based photoactive layers of efficient OPV devices. Local disorder in the EP-PDI aggregates is essential (i) for the optimum electron transport that is ensured by the efficient connectivity of the EP-PDI columns in adjacent EP-PDI domains and (ii) for preventing the stabilization of the neutral photoexcitations in the EP-PDI domains in the form of slowly diffusive excimers. The high photocurrent generation efficiency achieved suggests the EP-PDI excimers are formed faster than the activation of triplet states, and photocurrent losses are minimized.

Fast ultrahigh-density writing of low-conductivity patterns on semiconducting polymers.

The exceptional interest in improving the limitations of data storage, molecular electronics and optoelectronics has promoted the development of an ever increasing number of techniques used to pattern polymers at micro and nanoscale. Most of them rely on atomic force microscopy to thermally or electrostatically induce mass transport, thereby creating topographic features. Here we show that the mechanical interaction between the tip of the atomic force microscope and the surface of π-conjugated polymeric films produces a local increase of molecular disorder, inducing a localized lowering of the semiconductor conductivity, not associated to detectable modifications in the surface topography. This phenomenon allows for the swift production of low-conductivity patterns on the film surface at a speed exceeding 20 µm s⁻¹; paths have a resolution in the order of the tip size (20 nm) and are detected by a conducting-atomic force microscopy tip in the conductivity maps.

Efficient phosphorescent polymer yellow-light-emitting diodes based on solution-processed small molecular electron transporting layer.

Based on a solution-processed small molecular electron transporting layer, efficient multilayer solution-processed polymer yellow-light-emitting diodes were successfully fabricated. The maximum luminance efficiency and power efficiency reached 41.7 cd/A and 12.5 lm/W, respectively, which are comparable to and even over those from the PLEDs based on the vacuum-deposited electron-transporting layer. The solution-processed small molecular electron transporting layer is based on a mixture of three electron-transporting materials TmPyPB, TAZ, and TPBI. By utilization of this mixed system, not only the thickness of the electron-transporting layer can be easily adjusted, but also device efficiency can be improved because of their excellent synthetic properties.