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Planar perovskite solar cells using organic charge selective contacts were fabricated. In a vacuum deposited perovskite-based solar cell, dopant and additive free triazatruxene as the hole transport layer was introduced for device fabrication. High open-circuit voltage of 1090 mV was obtained using methylammonium lead iodide (Eg=1.55 eV) as light harvesting material, thus representing a loss of only 460 mV which is in close vicinity of mature silicon technology (400 mV). The devices showed a very competitive photovoltaic performance, monochromatic incident photon-to-electron conversion efficiency of 80% and the power conversion efficiencies in excess of 15% were measured with a negligible degree of hysteresis.

Triple cation based perovskite solar cells offer enhanced moisture tolerance and stability compared to mixed perovskites. Slight substitution of methyl ammonium or formamidinium cation by cesium (Cs+), was also reported to eliminate halide segregation due to its smaller size. To elucidate the device kinetics and understand the role of the Cs, we undertook different modes of scanning probe microscopy and electrochemical impedance spectroscopy (EIS) experiments. Kelvin probe force microscopy revealed that the incorporation of the Cs cation increases the contact potential difference (CPD), this CPD further increases when Spiro-OMeTAD is used as a hole transport material. The current at the nanoscale level shows improvement with Cs inclusion and further enhancement by the Spiro-OMeTAD deposition, studied under light illumination, which supports the high photocurrent density obtained from the cells. EIS demonstrates that in a triple cation environment, reduced carrier recombination at the TiO2/perovskite interface was also obtained which in turn allow us to achieve a higher Voc value.

Three-dimensional halide-based perovskites have emerged as promising semiconducting light harvesters for thin-film solar cell fabrication; however, their intrinsic instability under humidity restricts their potential commercialization. To address such challenges, the development of low-dimensional/layered Dion−Jacobson (DJ) phase perovskites has recently gained substantial attention due to their intriguing environmental stability and competitive power conversion efficiency. In this Review, we have screened and focused our investigation on the DJ phase in layered perovskites for solar cell fabrication, especially elucidation of the active role played by organic spacer cations. We also discuss the possible strategies that can be employed to further push the performance of DJ-based perovskite solar cells.

The electron and hole selective contact (SC) play a pivotal role in the performance of perovskite solar cells. In order to separate the interfacial phenomenon from bulk, the influence of charge SC was elucidated, by means of impedance spectroscopy. The specific role played by TiO2 and Spiro-OMeTAD as electron and hole SC in perovskite solar cells was investigated at short circuit condition at different temperatures. We have probed MAPbI3 and (FAPbI3)0.85(MAPbBr3)0.15 and elucidated parameters such as charge carrier mobility, recombination resistance, time constant and charge carrier kinetics in perovskite layer and at the interface of perovskite/SC. Charge carrier mobility in mixed perovskite was found to be nearly two order of magnitude higher as compared to MAPbI3. Moreover, the carrier mobility in devices with only electron SC was found to be higher as compared only hole SC. The charge accumulation at TiO2/perovskite/Spiro-OMeTAD interfaces were studied via frequency dependent capacitance, revealing higher charge accumulation at perovskite/Spiro-OMeTAD than at TiO2/perovskite interface. By performing varying temperature frequency dependent capacitance measurements the distribution of density of state within the bandgap of the perovskites, the emission rate of electrons from the trap states and traps activation energy was determined.

The electron and hole selective contact (SC) play a pivotal role in the performance of perovskite solar cells. In order to separate the interfacial phenomenon from bulk, the influence of charge SC was elucidated, by means of impedance spectroscopy. The specific role played by TiO2 and Spiro-OMeTAD as electron and hole SC in perovskite solar cells was investigated at short circuit condition at different temperatures. We have probed MAPbI3 and (FAPbI3)0.85(MAPbBr3)0.15 and elucidated parameters such as charge carrier mobility, recombination resistance, time constant and charge carrier kinetics in perovskite layer and at the interface of perovskite/SC. Charge carrier mobility in mixed perovskite was found to be nearly two order of magnitude higher as compared to MAPbI3. Moreover, the carrier mobility in devices with only electron SC was found to be higher as compared only hole SC. The charge accumulation at TiO2/perovskite/Spiro-OMeTAD interfaces were studied via frequency dependent capacitance, revealing higher charge accumulation at perovskite/Spiro-OMeTAD than at TiO2/perovskite interface. By performing varying temperature frequency dependent capacitance measurements the distribution of density of state within the bandgap of the perovskites, the emission rate of electrons from the trap states and traps activation energy was determined.

The performance of methylammonium lead triiodide (CH3NH3PbI3) based solar cells depends on its crystallization and controlled microstructure. In spite of its high performance, long-term stability is a paramount factor towards its large area fabrication and potential industrialization. Herein, we have employed poly(vinylidene fluoride−trifluoro ethylene) P(VDF-TrFE) as an additive into a low concentration based perovskite precursor solutions to control the crystallinity and microstructure. Perovskite layers of lower thickness can be derived from low precursor concentration, however it often suffers from severe voids and roughness. Introducing judicious quantities of P(VDF-TrFE) can improve the surface coverage, smoothness as well as reduces the grain boundaries in the perovskite. An array of characterization techniques were utilized to probe the structural, microstructural and spectroscopic properties. Impedance spectra suggests, the P(VDF-TrFE) can improve the carrier lifetimes and reduce the charge transfer resistance, which in turn allows to improve photovoltaic performance. For an optimized concentration of P(VDF-TrFE), the fabricated semi-transparent solar cells yielded power conversion efficiency in excess of 10%, which supersede pristine devices along with improved stability. The device architect and the fabrication technique provide an effective route to fabricate cost effective and visible-light-semi-transparent perovskite solar cells.

Perovskite solar cells have attracted significant attention during the current decade owing to their efficacy and photovoltaics performance, which has reached a new milestone in the thin-film category. Perovskite solar cells have witnessed a remarkable 25.2 % light-to-electricity conversion efficiency; however, the toxicity of the commonly employed Pb counterpart towards humans as well as the environment, in addition to material instability, are current bottlenecks towards commercial application. The scientific community has explored other metal ions as substitutions for Pb, while preserving the unique properties of the material, to produce environment-friendly perovskites. In this Review, we highlight the recent developments and challenges of Pb-free halide perovskite-based light harvesters for solar cell applications. This summary is intended to aid in the further development of a materials library for this sustainable technology.

Three-dimensional hybrid perovskite materials (CH3 NH3 PbI3 ) suffer from intrinsic instability owing to organic cation evaporation and ion migration. The inclusion of a large organic cation such as guanidinium has been probed to stabilize the structure. This work proposes the inclusion of imidazolium iodide (C3 N2 H5 I) as an organic cation inside the CH3 NH3 PbI3 matrix, as a reservoir to control the spontaneous loss of iodide. The introduction of imidazolium iodide in amounts below 20 % has an impact on the crystallization process but not on the optical properties. It also positively controls non-radiative recombination and improves the open-circuit voltage of the solar cells. The present study paves way for a deeper insight into the limit of multi-dimensional perovskite to further push the performance.

The rapid development in the field of organo-metal halide perovskite solar cells (PSCs) has led to the report of power conversion efficiency of>25%. However, their large-scale deployment and possible commercialization endeavor are currently limited due to the presence of high-temperature processed electron transport material (ETM) such as TiO2 and the expensive hole transport material (HTM) in the state-of-the-art devices. By em- ploying Solar Cell Capacitance Simulator (SCAPS)-1D, we attempted to propose low cost charge selective ma- terials as ETM and HTM, which can deliver high photovoltaic performance. For this, the evaluation of TiO2, ZnO and SnO2 as ETMs was validated. Besides this, the role of thickness of ETMs was also investigated in a PSCs using CH3NH3PbI3 as light harvester and Spiro-OMeTAD as HTM. Our simulation results suggests that 90 nm of SnO2 layer outperforms as ETM for device fabrication. Furthermore, in our pursuit to avoid the usage of Spiro- OMeTAD, different organic and inorganic HTMs (P3HT, CuSbS2,Cu2O, CuSCN) have been investigated, and specifically the HTM thickness was optimized for high performance. We have found that by using the config- uration of FTO/SnO2 (90 nm)/MAPbI3/CuSCN (100 nm)/Au a PCE of 26.74% with a Voc of 1180 mV can be acheived. The role of metal cathode work function was also studied to replace the expensive gold (Au) electrode.

Precision control of charge transport can provide a solid basis for the design of materials with novel properties. We report on the bottom-up fabrication and study of the electronic properties of molecular multijunction networks comprising ultrafine gold nanoparticles (AuNPs) of diameter ∼1.4 nm, electronically linked by means of copper 3-diethylamino-1-propylsulfonamide sulfonic acid-substituted phthalocyanine (CuPcSu) molecules. When electrons flow through the nonlinked nanoparticle arrays, they experience onsite Coulomb repulsion and are strongly localized, with a localization length ξ = 0.7 nm. Under dynamic excitation the system functions as a single electron-transport regulator, undergoing Coulomb oscillations, whereas the introduction of CuPcSu molecules results in the formation of a network of multiple molecular/Au nanojunctions and conductance increases by five orders of magnitude. This switching behavior functions on reversible redox reactions and pushes carriers into a state of weaker localization. In this state, electrons spread over several junctions and all temperature-scaled current versus voltage curves, J/T1 + α versus eV/kT, collapse into one universal curve, characterizing the network and the extent of its disorder. Utilizing this property, we demonstrate the effect of interelectrode distance on the conduction nodes' topological disorder. The system consists a promising candidate for Au NPs-based thin films with tunable properties wherever solution-based fabrication methods, such as injection printing, are envisioned.

Hysteresis is one of the most remarkable features of perovskite solar cells; however, it is also present in other kinds of devices such as dye-sensitized solar cells. Hysteresis is due to underlying slow dynamic processes that interfere with the process of charge separation which depends critically on the selective contacts used. In this work we focus on the low-frequency (0.1–10 Hz) dynamics using impedance and intensity-modulated photocurrent spectroscopy and found that both perovskite solar cells (PSCs) and “viscous electrolyte containing” dye-sensitized solar cells (DSSCs) can be described on the same fundamental grounds. By comparing different electrolyte compositions in DSSCs and both methylammonium and formamidinium-based PSCs, we find a connection between the polar nature of the cations and the low-frequency component of these solar cells. There is evidence that in both cases ion transport and specific chemical interactions with the TiO2 surface give rise to the slow dynamics and the hysteresis. This is mainly inferred from the slope of the capacitance vs. applied voltage which shows accumulation behavior for the formulations with higher dipole moments only.

Solution-processed photovoltaics employing perovskite as light harvester are the next generation future energy source owing to its low manufacturing cost and potential to achieve high power conversion efficiency. Significant emphasis has been laid on the performance-related investigations, however the long-term instability under operational conditions and device reproducibility obstruct its potential commercial endeavour. Herein, by tweaking the energy level alignment between the hole-transport layer and perovskite, by the placement of a 2D-MoS2 interlayer, we demonstrate suppressed interfacial charge accumulation, fast charge extraction, and subsequently improved photovoltaic performances. Notably, with the usage of a dopant free hole transport materials, a power conversion efficiency of 18.54% with significantly upgraded open circuit voltage (Voc) and FF was recorded. The stability measurement shows that the resulting 2D-MoS2 supported dopant-free hole selective layers exhibit notable moisture stability under ambient conditions. Our study put forward the profound experimental understanding of 2D-transition metal dichalcogenides as an agent to engineering the interface, enlightening the power conversion efficiency and lifetime of the perovskite solar cells.

This work reports experimental evidence of a photovoltaic effect in transparent UV-selective Zn(O,S) based heterojunctions. Zn(O,S) has a strong interest for the development of UV-selective solar cells with high transparency in the visible region, required for the development of nonintrusive building-integrated pho- tovoltaic (BIPV) elements as transparent solar windows and glass-based solar façades. By anion alloying, Zn(O,S) mixed crystal absorbers can be fabricated with different sulfur content across the whole compositional range. This allows adjustment of the bandgap of the absorbers in the 2.7–2.9 eV region, maximizing absorption in the UV, while keeping a high level of transparency. Zn(O,S) alloys with composition corresponding to S/(S þ O) content ratios of 0.6 are successfully grown by sputtering deposition, and first glass/FTO/NiO/Zn(O,S)/ITO device prototypes are produced. The resulting device present an average visible transmittance (AVT) of 75% and present photovoltaic effect. By introducing a thin C60 film as electron transport layer (ETL), charge extraction is enhanced, and devices show an efficiency of 0.5% and an AVT > 69%. The transparency of these devices can potentially allow for their ubiquitous installation in glazing systems as part of nonintrusive BIPV elements or to power Internet of Things (IoT) devices and sensors as an integrated transparent component., This work has received funding from the European Union H2020 Framework Programme under Grant Agreement no. 826002 (Tech4Win). Authors from IREC and Universitat de Barcelona belong to the SEMS (Solar Energy Materials and Systems) Consolidated Research Group of the "Generalitat de Catalunya" (Ref. 2017 SGR 862). D.P. thanks to the funding from the Basque Country PI2018-08 (PISCES). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 712949 (TECNIOspring PLUS) and the Government of Catalonia's Agency for Business Competitiveness (ACCIÓ).

Interface engineering has become one of the facile and effective approach to improve solar cells performance, its long-term stability and retard unwanted side reaction. We have developed three passivating agents which can functionalize the surface and induce hydrophobicity by employing substituted thiazolium iodide (TMI) for perovskite solar cells fabrication. The role of TMI interfacial layers on microstructure and electro-optical properties was assessed for structural as well as transient absorption (TA) measurements. TMI treatment resulted into VOC and FF enhancement by reducing possible recombination paths at perovskite/HTM interface and by reducing the shallow as well as deep traps. These in turn allowed to achieve higher performance as compared to the pristine surface. Additionally, TMI passivated perovskite layer reduces considerably CH3NH3+ thermal diffusion and degradation induced by humidity. The un-encapsulated perovskite solar cells employing TMI exhibited a remarkable stability under moisture levels (~50% RH) retaining ~95% of initial PCE after 800 h of fabrication, paving potential scalable endeavour.

Three-dimensional hybrid perovskite materials (CH

We propose and investigate a nanoscale multi-junction network architecture that can be configured on-flight to perform Boolean logic functions at room temperature. The device exploits the electronic properties of randomly deposited molecule-interconnected metal nanoparticles, which act collectively as strongly nonlinear single-electron transistors. Disorder is being incorporated in the modeling of their electrical behavior and the collective response of interacting nano-components is being rationalized. The non-optimized energy consumption of the synaptic grid for a "then-if" logical computation is in the range of few aJ.

Summary The use of hydrophobic dopant is paramount for the success of organic semiconductors. Here we demonstrate the use of an N-heterocyclic hydrophobic ionic liquid, 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide (BMPyTFSI), to induce dual functionality: as p-type dopant and as additive for state-of-the-art Spiro-OMeTAD hole-transporting material (HTM). This ionic liquid doped HTM was then implemented for perovskite solar cell fabrication and delivered competitive results. The dopant has the ability to substitute state-of-the-art ultra-hygroscopic lithium salt (LiTFSI) and problematic 4-tert-butylpyridine (t-BP) additive. BMPyTFSI was found to increase the conductivity of Spiro-OMeTAD and its use as dopant in HTM reduces charge recombination, improves the film formation by reducing the pinholes on the HTM surface, and allows fabrication of efficient devices. Competitive air stability of solar cells in comparison with their state-of-the-art dopant was found, and these findings open up a broad range of organic semiconductors for hydrophobic ionic liquid-based doping.

The aggregation kinetics of negatively charged borate-stabilized silver nanoparticles (NPs) induced by the cationic regioregular polythiophene polyelectrolyte poly{3-[6-(1-methylimidazolium-3-yl)hexyl]thiophene-2,5-diyl bromide} (PMHT-Br) and the morphology of formed aggregates have been investigated via ultraviolet-visible light (UV-vis) spectroscopy, transmission electron microscopy (TEM), zeta (ζ) potential measurements, dynamic light scattering (DLS), and time-resolved small-angle X-ray scattering (SAXS). Two or three populations of NPs are formed within milliseconds upon mixing the components, which differ in the mean size, extent of polymer coating, and time stability. These characteristics are primarily controlled by the PMHT-Br to Ag-NPs ratio. Population of single NPs of a mean size of ∼5 nm is present in every system and is mostly stable for a long time. At low ratios, the single NPs are most probably almost free of polymer chains and the second population includes slow, but in a limited extent, growing NPs in which single NPs might be interconnected by polymer chains. At the ratios corresponding to the charge balance in the system (ca. zero ζ-potential of NPs), the NPs aggregate, forming a second population that continuously grows in size, and finally undergo sedimentation. At the high ratios, three long-time stable populations of NPs are observed, having mean sizes of ca. 5, 13, and 35 nm; all NPs should be fully coated with PMHT-Br, giving them a positively charged stabilizing shell.

Triazatruxene core based hole transporting materials (HTMs), HMDI (5,10,15-trihexyl-3,8,13-trimethoxy-10,15-dihydro-5H-diindolo[3,2-a: 3',2'-c]carbazole) and HPDI (5,10,15-tris(4-(hexyloxy)phenyl)-10,15-dihydro-5H-diindolo[3,2-a: 3',2'-c]carbazole) were synthesized and exploited in perovskite based solar cells. The energy levels of star-shaped HMDI and HPDI were tuned by symmetrically introducing electron-rich alkoxy side groups. These soluble and easily synthesized materials exhibit optical transparency in the visible region, high thermal stability and have suitable HOMO values with respect to perovskite, making them an ideal HTM candidate for efficient perovskite solar cells. The HPDI molecule-based devices gave competitive power conversion efficiencies of similar to 11% under AM 1.5G illumination. The facile synthetic approach using inexpensive precursor materials will facilitate triazatruxene-based molecules to be further exploited in thin film organic-inorganic perovskite solar cells and needs optimization to enhance power conversion efficiency.

A solution processable, molecular organic semiconductor, 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene), was employed as hole transport material (HTM) in mesoscopic methylammonium lead iodide perovskite solar cells. TIPS-pentacene is potentially cost effective, exhibits a relatively high hole mobility and has a favourable HOMO level with respect to the valence band of perovskite. The photovoltaic performance of perovskite solar cells with TIPS-pentacene as HTM in its pristine form and with a dopant/additive was investigated and compared with classical spiro-OMeTAD based devices. Through solvoneering (solvent engineering) and concentration optimization TIPS-pentacene in its pristine form gave a very competitive power conversion efficiency (PCE) of 11.8% under 1 sun conditions. The open circuit voltage of 0.92 V and a short circuit current density of 20.86 mA cm(-2) for the devices with pristine TIPS-pentacene were higher compared to doped spiro-OMeTAD based devices under similar conditions, thus paving the use of TIPS-pentacene as an alternative to an expensive spiro-OMeTAD for large area integration in perovskite based solar cells.

LiFePO4 electrodes were built in different architectures using a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) mixed conductor as an additive. Conductivity enhancement of PEDOT:PSS was achieved by the addition of ethylene glycol and dimethyl sulfoxide solvents. The amounts of conducting polymer and solvent additives strongly influence the discharge capacity and potential of LiFePO4 electrodes at high rates. The initial impedance and the direct current resistance were correlated with the discharge performance at high rates. The optimized amount of PEDOT:PSS added within the bulk resulted in a lower value of impedance, lower load resistance and higher capacity as compared to the standard preparation. Furthermore 57Fe Mossbauer spectroscopy and X-ray photoelectron spectroscopy were employed to probe the bulk transformation of the LiFePO4 active material and the surface changes of the composite electrodes with the conducting polymer upon lithiation. The electrode with PEDOT:PSS coated on the aluminium current collector and doped with ethylene glycol showed highly competitive performance (132 mA h g−1 at 5 C and 145 mA h g−1 at 2 C for 50 cycles).

Special Issue: Perovskite Optoelectronics, Organohalide perovskites have emerged as highly promising replacements for thin-film solar cells. However, their poor stability under ambient conditions remains problematic, hindering commercial exploitation. The addition of a fluorous-functionalized imidazolium cation during the preparation of a highly stable cesium-based mixed perovskite material Cs(MAFA)Pb(IBr) (MA=methylammonium; FA=formamidinium) has been shown to influence its stability. The resulting materials, which vary according to the amount of the fluorous-functionalized imidazolium cation present during fabrication, display a prolonged tolerance to atmospheric humidity (>100 days) along with power conversion efficiencies exceeding 16 %. This work provides a general route that can be implemented in a variety of perovskites and highlights a promising way to increase perovskite solar cell stability., M.A.F. acknowledged financial support from the CSIC (PIE‐201760E002).

During the last years, perovskite solar cells have gained increasing interest among the photovoltaic community, in particularly after reaching performances at par with mature thin film based PV. This rapid evolution has been fostered by the compositional engineering of perovskite and new device architectures. In the present work, we report the fabrication of perovskite solar cells based on highly ordered 1-dimensional vertically oriented TiO nano-forests. These vertically oriented porous TiO photoanodes were deposited by physical vapor deposition in an oblique angle configuration, a method which is scalable to fabricate large area devices. Mixed (MAFA)Pb(IBr) or triple cation Cs(MAFA)Pb(IBr) based perovskites were then infiltrated into these 1-dimensional nanostructures and power conversion efficiencies of 16.8% along with improved stability was obtained. The devices fabricated using 1D-TiO were found to be more stable compare to the classical 3-dimensional TiO photoanodes prepared by wet chemistry. These 1-D photoanodes will be of interest for scaling up the technology and in other opto-electrical devices as they can be easily fabricated utilizing industrially adapted methodologies., We thank Laura Calio for help with coloration of SEM images and ARG thanks EU-FEDER funds and the MINECO (projects MAT2013-40852-R and MAT2016-79866-R) for financial support. MINECO/ICTI2013-2016/MAT2016-79866-R

Towards increasing the stability of perovskite solar cells, the addition of Cs

Es geschieht nicht oft, dass die Forschung auf ein Material stost, das zu grosten Hoffnungen Anlass gibt und von verschiedenster Seite Interesse erfahrt. Wenn es geschieht, verlauft die Entwicklung rasant. Ein solches Material ist Perowskit, das ganzlich neue Konzepte in der Energieumwandlung angestosen hat. Perowskite sind aufgrund ihrer panchromatischen Lichtabsorption und ihrem ambipolaren Verhalten von herausragendem Interesse als Material fur die Photovoltaik. Der maximale Wirkungsgrad von Perowskit-Solarzellen hat sich in weniger als einem Jahr verdoppelt und erreicht nun Werte von 15 % unter Laborbedingungen. Dies ist besonders markant in einem wissenschaftlichen und industriellen Umfeld, in dem jede Steigerung in der Nachkommastelle als Erfolg gefeiert und breit diskutiert wird. Wir fassen hier den Stand der Forschung bei der Verwendung von Perowskitmaterialien fur Solarzellen zusammen.

This study explores the excitation wavelength and fluence dependence of processes occurring in formamidinium lead triiodide (FAPbI3) film using time-resolved transient absorption and terahertz spectroscopies. The results indicate that second-order processes are responsible for charge carrier recombination at low fluences of the absorbed photons (below 8.4 × 1012 ph per cm2). An increase in fluence leads to the appearance and successive reduction of the time component assigned to the Auger recombination of free charge carriers (240–120 ps). Simultaneously, the bimolecular recombination time decreases from ∼1400 to ∼700 ps. Further increasing the pump fluence produces an exciton population that recombines in 6 ps. The comparison of two characteristic bleaching bands located at 480 and 775 nm provides evidence for the validity of the two valence bands model. Excitation with higher fluences results in a marked difference in the probed dynamics at these bands, reflecting the action of two excited states at the conduction band. Our results demonstrate that a single model cannot be applied in characterizing the perovskite absorber transitions at all pump fluences. These findings are relevant in understanding their operating mechanism under specific experimental conditions, which should differ for perovskite based solar cells, lasing media or photon detectors.

The pressure to move towards renewable energy has inspired researchers to look for ideas in photovoltaics that may lead to a major breakthrough. Recently the use of perovskites as a light harvester has lead to stunning progress. The power conversion efficiency of perovskite solar cells is now approaching parity (>22 %) with that of the established technology which took decades to reach this level of performance. The use of a hole transport material (HTM) remains indispensable in perovskite solar cells. Perovskites can conduct holes, but they are present at low levels, and for efficient charge extraction a HTM layer is a prerequisite. Herein we provide an overview of the diverse types of HTM available, from organic to inorganic, in the hope of encouraging further research and the optimization of these materials.

We demonstrate for the first time, the real lifetime response of mixed halide perovskite solar cells (PSCs) for >1000 h under outdoor conditions and the exceptional photoresponse observed at low-light intensities attributed to the ionic-electronic nature of the material. The investigated devices were fabricated by utilizing mixed perovskites containing formamidinium (FA) and methylammonium (MA) cations, in a one step solution-process method through a solvent engineering approach. The devices’ architecture is FTO/TiO (blocking layer) TiO (mesoporous)/FAPbIMAPbBr/Spiro-OMeTAD/Au. Notably, low short circuit current (J) was observed at low light intensities (1000 h under real outdoor conditions and the strong ionic component observed at low light irradiation., CN2 acknowledges the support of the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2013-0295, for the Grants ENE2013-48816-C5-4-R, ENE2016-79282-C5-2-R and the Nanoselect Excelence Network MAT2015-68994-REDC. To the Agència de Gestió d'Ajuts Universitaris i de Recerca for the support to consolidated Catalonia research group 2014SGR-1212 and the Xarxa de Referència en Materials Avançats per a l'Energia (Xarmae). To the COST Action StableNextSol ProjectMP1307. To CONACYT for the PhD awarded to Y.R.

Lead halide based perovskite solar cells are presently the flagship among the third generation solution-processed photovoltaic technologies. The organic cation part in the perovskite plays an important role in terms of crystal structure tuning from tetragonal to trigonal or pseudocubic or vice versa depending on the organic cations used, while it also displays different microstructure. In this paper, we demonstrate the influence of the organic cation part with respect to optical properties, hysteresis behavior, and stability. This study offers a clear understanding of the perovskite properties and how they can be modulated by compositional engineering. With a rational choice, light harvesting abilities and hysteresis behavior can be controlled in these systems. The substitution of formamidinium cation by methylammonium cation allows achieving low temperature annealing and inducing stability in perovskites together with enhanced photovoltaic properties. By the use of in-situ scanning force microscopy experiments the conversion of precursors to perovskite at a particular temperature can be visualized.

A new series of pyrrole family, N-substituted phenyl attached alkyl at the ortho, meta and para position were synthesized by a straight forward method and were exploited as an innovative monomer for electroactive polymers. Ionic liquids were employed as a medium for electro-polymerization of these monomers to obtain N-(methyl)phenyl polypyrroles. N-substituted polypyrroles show different morphologies and conductivity according to position of methyl group on the benzene ring and synthesis medium. The electrical conductivity value varies with the position of methyl group and was >10 −5 S/cm, higher than the sample obtained from conventional media. The resulting polymer films were characterized by FT-IR and UV–Vis spectroscopy, contact angle measurements, cyclic voltammetry and scanning probe microscopic technique along with their electrochromic behavior.

The electropolymerization of pyrrole in ionic liquid media was carried out to produce an adherent, uniform, and durable polypyrrole (PPy) films with enhanced electrical properties. A threefold increase in the conductivity value can be attained with the selective choice of polymerizing media and ambient temperature dc conductivity value of 43, 15, and 13 S cm−1 for films grown in 1-ethyl-3-methylimidazolium bis(perfluoroethanesulfonyl)imide, 1-ethyl-3-methylimidazolium triflate and in lithium triflate in acetonitrile respectively. The corresponding localization lengths were found to be 17, 33, and 48 nm indicate that carriers are strongly localized. At low temperature, all three types of PPy films show metallic type behavior. Though transition is observed above 200 K for all the three films, the charge transport mechanism remains unaltered at higher temperatures for the films grown in ionic liquids, while the film grown in lithium triflate in acetonitrile assumes a three-dimensional variable range hopping conduction behavior. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

In recent years, organo-halide perovskite solar cells have garnered a surge of interest due to their high performance and low-cost fabrication processing. Owing to the multilayer architecture of perovskite solar cells, interface not only has a pivotal role to play in performance, but also influences long-term stability. Here we have employed diverse morphologies of electron selective layer (ESL) to elucidate charge extraction behavior in perovskite solar cells. The TiO2mesoporous structure (three-dimensional) having varied thickness, and nanocolumns (1-dimensional) with tunable length were employed. We found that a TiO2electron selective layer with thickness of about c.a. 100 nm, irrespective of its microstructure, was optimal for efficient charge extraction. Furthermore, by employing impedance spectroscopy at different excitation wavelengths, we studied the nature of recombination and its dependence on the charge generation profile, and results showed that, irrespective of the wavelength region, the fresh devices do not possess any preferential recombination site, and recombination process is governed by the bulk of the perovskite layer. Moreover, depending on the type of ESL, a different recombination mechanism was observed that influences the final behavior of the devices.

Conjugated polymers have high potential for efficient production of low-cost flexible optoelectronics devices such as solar cells, photodiodes and light emitting diodes. In this paper, the interaction between poly [2-methoxy-5 (2′-ethyl hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and acridine orange (AO) dye has been studied to examine the role of charge pair separation and photocurrent generation in organic photovoltaic films. The AO dye concentration has been optimized on the basis of absorption spectra and photoluminescence (PL) studies carried over the films particularly, for photovoltaic applications. For this purpose, MEH-PPV polymer was dissolved in n -butyl acetate and doped with different concentration of AO dye solution. The Current–Voltage characteristics of MEH-PPV films, prepared by spin-coating technique on ITO-coated glass substrate have been determined as a function of temperature. For the cathode contact, Al was deposited using RF sputtering technique so that the current is predominantly due to holes. The conductivity increases by two orders of magnitude as the AO dye concentration increases to 2.65 mol L −1 . In optical properties, we have studied the UV–visible absorption spectra, PL spectra of undoped and doped MEH-PPV films. The absorption studies show that the addition of AO dye does not significantly change (reduce) the absorption, which indicates the suitability of photon absorption. The PL spectra were recorded for MEH-PPV films, which become narrow on increasing the AO dye concentration. The PL studies indicate that up to certain concentration of AO dye in MEH-PPV films, PL intensity decreases as compare to that for undoped MEH-PPV film. The combined effect of increase in conductivity by two orders, decrease in PL intensity and no significant change in absorption makes the material suitable for photovoltaic applications.

The electrical properties of poly[2-methoxy-5-(2′-ethyl hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) films were studied at different concentrations of acridine orange (AO) dye in the temperature range (293–416 K). MEH-PPV was dissolved in n-butyl acetate and was doped with different concentrations of AO dye solution. The MEH-PPV films were prepared by spin-coating technique with the speed of 1000 rpm. For conductivity measurements, Cu electrode contacts in planar configuration were made on the top surface of the film by RF sputtering. The DC conductivity and steady-state photoconductivity measurements were performed on these spin-coated thin films. It was observed that the doping of AO dye reduces the electrical resistivity as well as activation energies and enhances DC conductivity and photoconductivity. An increase in DC conductivity can be explained in terms of hopping conduction in the wide range of localised states. Photoconductivity measurements are useful in determining the nature of optical charge generation and transport in conjugated polymers. The value of T0 (measurement of disorderness) is in good agreement with the XRD spectra, which depicts the amorphous nature of the pure MEH-PPV film. Photocurrent dependence on incident radiation has also been observed which follows the power law (Iph∝Fγ). This dependence shows that the recombination with in the localised state is predominant.

In the present paper, we have reported the chemical synthesis and characterization of polyaniline doped with tellurium. The aniline was polymerized by chemical oxidation using ammonium persulphate as an oxidant and was doped with different concentrations of tellurium. Doped PANI was characterized by using FTIR, DSC and two-probe conductivity measurement. The dc conductivity has been measured to see the effect of tellurium and its mechanism has been explained by the formation of polarons and bipolarons that move along the polymer chain, and gives rise to the electrical conductivity. The observed increase in conductivity of polyaniline is attributed due to the incorporation of Te into the PANI chain. Glass transition temperature ( T g ) and enthalpy (Δ H ) have been calculated from DSC measurements. FTIR spectra suggest the structural changes after incorporation of Te in polymeric chain.

We report on studies of the formamidinium lead triiodide (FAPbI3) perovskite film using time-resolved terahertz (THz) spectroscopy (TRTS) and flash photolysis to explore charge carriers generation, migration, and recombination. The TRTS results show that upon femtosecond excitation above the absorption edge, the initial high photoconductivity (∼75 cm(2) V(-1) s(-1)) remains constant at least up to 8 ns, which corresponds to a diffusion length of 25 μm. Pumping below the absorption edge results in a mobility of 40 cm(2) V(-1) s(-1) suggesting lower mobility of charge carriers located at the bottom of the conduction band or shallow sub-bandgap states. Furthermore, analysis of the THz kinetics reveals rising components of1 and 20 ps, reflecting dissociation of excitons having different binding energies. Flash photolysis experiments indicate that trapped charge carriers persist for milliseconds.

The electron dynamics of solar cells with mesoporous TiO2 contact is studied by electrochemical small-perturbation techniques. The study involved dye solar cells (DSC), solid-state perovskite solar cells (SSPSC), and devices where the perovskite acts as sensitizer in a liquid-junction device. Using a transport-recombination continuity equation we found that mid-frequency time constants are proper lifetimes that determine the current-voltage curve. This is not the case for the SSPSC, where a lifetime of ∼1 μs, 1 order of magnitude longer, is required to reproduce the current-voltage curve. This mismatch is attributed to the dielectric response on the mid-frequency component. Correcting for this effect, lifetimes lie on a common exponential trend with respect to open-circuit voltage. Electron transport times share a common trend line too. This universal behavior of lifetimes and transport times suggests that the main difference between the cells is the power to populate the mesoporous TiO2 contact with electrons.

Four center symmetrical star-shaped hole transporting materials (HTMs) comprising planar triazatruxene core and electron-rich methoxy-engineered side arms have been synthesized and successfully employed in (FAPbI(3))(0.85)(MAPbBr(3))(0.15) perovskite solar cells. These HTMs are obtained from relatively cheap starting materials by adopting facile preparation procedure, without using expensive and complicated purification techniques. Developed compounds have suitable highest occupied molecular orbitals (HOMO) with respect to the valence band level of the perovskite, and time-resolved photoluminescence indicates that hole injection from the valence band of perovskite into the HOMO of triazatruxene-based HTMs is relatively more efficient as compared to that of well-studied spiro-OMeTAD. Remarkable power conversion efficiency over 18% was achieved using 5,10,15-trihexyl-3,8,13-tris (4-methoxyphenyl)-10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole (KR131) with compositive perovsldte absorber. This result demonstrates triazatruxene-based compounds as a new class of HTM for the fabrication of highly efficient perovskite 4 solar cells.

It is not often that the scientific community is blessed with a material, which brings enormous hopes and receives special attention. When it does, it expands at a rapid pace and its every dimension creates curiosity. One such material is perovskite, which has triggered the development of new device architectures in energy conversion. Perovskites are of great interest in photovoltaic devices due to their panchromatic light absorption and ambipolar behavior. Power conversion efficiencies have been doubled in less than a year and over 15% is being now measured in labs. Every digit increment in efficiency is being celebrated widely in the scientific community and is being discussed in industry. Here we provide a summary on the use of perovskite for inexpensive solar cells fabrication. It will not be unrealistic to speculate that one day perovskite-based solar cells can match the capability and capacity of existing technologies.

A simple and facile method was used to synthesize polyaniline (PANI) nanocomposites with sodium montmorillonite clay (Na+-MMT) using in situ intercalative oxidative polymerization. Aniline was admixed with Na+-MMT at various concentrations, keeping the aniline monomer in the reaction mixture constant. The intercalation of PANI into the clay layers was confirmed by X-ray diffraction studies in conjugation with electron microscope techniques and FTIR spectra, particularly by the narrowing of the Si–O stretching vibration band confirmed the interaction between PANI and the clay. The employed route offers the possibility to improve the thermal properties with simultaneously controlled electrical conductivity. Thermal studies show an improved thermal stability of the nanocomposites relative to the pure PANI. Depending on the loading of the clay, the room temperature conductivity values of these nanocomposites varied between 2.0 × 10−4 and 7.4 × 10−4 S cm−1, with the maximum at 44 wt% PANI concentration. The decrease of electrical conductivity at high PANI concentration was ascribed to the decrease of the structural ordering of PANI in the nanocomposite.

International audience; Aggregated systems of silver (Ag) and gold (Au) nanoparticles coated with cationic polythiophene were prepared, which showed optical properties typical for strongly coupled plasmonic excitations. The procedure allowed tune up the three-dimensional arrangement of nanoparticles assembly for achieving strong SERS effect at the excitation wavelength depending on the polymer concentration. By combination with an anionic derivative of polythiophene thin multilayer films composed of alternating anionic and cationic polythiophene with mutually interacting plasmonic Au nanoparticles were successfully prepared using layer-by-layer deposition.