Perovskite Based Solar Cells

This paper reports on grain boundary (GB) roles in lead-free tin halide perovskite thin films. Nano scale spatial mapping of charge separation efficiency in methylammonium tin halide (MASn(I 1−x Br x) 3 , MA=CH 3 NH 3) thin films were constructed by Kelvin probe force microscopy and conductive atomic force microscopy (C-AFM). We observed downward band bending at GBs under dark conditions and higher surface photovoltage along the GBs, confirmed by C-AFM which showed high local current flows along the GBs. The band bending degree and local current intensity were affected by the Br/I ratio. Photo-generated carriers were more effectively separated and collected at GBs with increased Br content, and hysteresis was observed in Br-rich Sn-halide perovskite. Supplementary material for this article is available online

Hole transporting material (HTM) is a significant component to achieve the high performance perovskite solar cells (PSCs). Over the years, inorganic, organic and hybrid (organic-inorganic) material based HTMs have been developed and investigated successfully. Today, perovskite solar cells achieved the efficiency of 22.1 % with with 2,2',7,7'-tetrakis(N,N-dip -methoxyphenyl-amine) 9,9-spirobifluorene (spiro-OMeTAD) as HTM. Nevertheless, synthesis and cost of organic HTMs is a major challenging issue and therefore alternative materials are required. From the past few years, inorganic HTMs showed large improvement in power conversion efficiency (PCE) and stability. Recently CuO x reached the PCE of 19.0% with better stability. These developments affirms that inorganic HTMs are better alternativesto the organic HTMs for next generation PSCs. In this report, we mainly focussed on the recent advances of inorganic and hybrid HTMs for PSCs and highlighted the efficiency and stability of PSCs improved by changing metal oxides as HTMs. Consequently, we expect that energy levels of these inorganic HTMs matches very well with the valence band of perovskites and improved efficiency helps in future practical deployment of low cost PSCs.

This review summarizes the optical and electrical models of bulk heterojunction (BHJ) polymer solar cells (PSCs) and numerically simulates and analyzes the performance of the PSCs. A complete simulation of a conventional BHJ device based on the polymer P3HT is presented and results are compared with the experimental data. Key factors affecting the device performance, including the photo absorption, quantum efficiency, short-circuit current, fill factor, and open-circuit voltage of the device, are analyzed and summarized. Simulations on inverted, semitransparent, and large-area PSCs are performed and findings are compared with experimental results. Simulations reveal the effects of optical spacer layers, different thicknesses, carrier mobilities, light intensities, contact barriers, effective bandgaps, recombination coefficients, and energy-level bending on the quantum efficiency, short-circuit current, fill factor, and open-circuit voltage of the PSCs. Differences between conventional and inverted geometry, opacity and semitransparency, and small and large-area PSCs are discussed based on the simulations. A power conversion efficiency of 11.0% is predicted for the PSC based on P3HT. Results suggest the need to further reduce the series resistance in large-area PSCs.

A B S T R A C T Although revolutionary progress in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) greater than 22% has accompanied significant advances in materials engineering, processing, and device architectures, the selection of proper hole transporting materials (HTMs) is still critical for high efficiency, low-cost and long-term stability. The PSCs community is actively investigating a group of HTMs for high efficiency and long-term stability with commercial viability. In this context, inorganic nickel oxide (NiO x)-HTMs possess the advantages of energetically favorable energy band positions, high hole mobility, superior chemical stability, and low cost manufacturing. Herein, we address the initial breakthroughs and recent progress in NiO x-HTMs for PSCs. In addition to synthetic routes and deposition techniques used for NiO x-HTMs in two major device architectures (p-in and n-i-p structure), the stability and cost-breakdown of PSCs are evaluated in details. Finally, future directions for further improvements on issues such as high efficiency, stability and low-cost of PSCs based on NiO x-HTMs are also provided.

In this work, the effect of some parameters on tin-based perovskite (CH3NH3SnI3) solar cell were studied through device simulation with respect to adjusting the doping concentration of the perovskite absorption layer, its thickness and the electron affinities of the electron transport medium and hole transport medium, as well as the defect density of the perovskite absorption layer and hole mobility of hole transport material (HTM). A device simulator; the one-dimensional Solar Cells Capacitance Simulator (SCAPS‑1D) program was used for simulating the tin-based perovskite solar cells. The current-voltage (J-V) characteristic curve obtained by simulating the device without optimization shows output cell parameters which include; open circuit voltage (Voc) = 0.64V, short circuit current density (Isc) = 28.50mA/, fill factor (FF) = 61.10%, and power conversion efficiency (PCE) = 11.30% under AM1.5 simulated sunlight of 100mW/cm2 at 300K. After optimization, values of the doping concent...

A B S T R A C T Quantum dot (QD) sensitized solar cells have been receiving significant attention because of their potential to replace the existing conventional solar cells as low cost and high efficiency alternatives. This widespread attention has generated a large number of published research papers in the field that were recently reviewed. The challenge in reviewing the literature is in transforming the collected technical information generated through independently conducted perturbation experiments into an alternative point of view. A unique approach based on inferential statistics is explained and applied to reviewed QD based solar cells data. Analyzing the data in this fashion has provided us new and previously unknown insight into the operation and functioning of solar cells as well as the relative quantitative importance of each variable involved in determining the properties of interest in solar cells. This methodology is very powerful and can be applied to gain insight through reviewing the published data in any field of science to set the direction for ongoing and future research. In addition, the response surface methodology is explained and used to predict the reachable optimum efficiency of 20% with a given set of materials combination given the current state of the art.

Highlights • Simulation study of perovskite solar cells with p–i–n structure in the configuration Cu:NiO x /MAPbX/ZnO/Al. • Solar cells with MAPbI 2 Br photoactive layers exhibit best conversion efficiency and show promise of high thermal stability. • Simulation results provide a better understanding of the defect density and thickness of the active perovskite layer. Abstract Although perovskite solar cells with power conversion efficiencies (PCEs) more than 22% have been realized with expensive organic charge-transporting materials, their stability and high cost remain to be addressed. In this work, the perovskite configuration of MAPbX (MA = CH 3 NH 3 , X = I 3 , Br 3 , or I 2 Br) integrated with stable and low-cost Cu:NiO x hole-transporting material, ZnO electron-transporting material, and Al counter electrode was modeled as a planar PSC and studied theoretically. A solar cell simulation program (wxAMPS), which served as an update of the popular solar cell simulation tool (AMPS: Analysis of Microelectronic and Photonic Structures), was used. The study yielded a detailed understanding of the role of each component in the solar cell and its effect on the photovoltaic parameters as a whole. The bandgap of active materials and operating temperature of the modeled solar cell were shown to influence the solar cell performance in a significant way. Further, the simulation results reveal a strong dependence of photovoltaic parameters on the thickness and defect density of the light-absorbing

In this report, two simple cost efficient solution processable small molecular hole transporting materials (HTMs) are synthesized and used successfully in inverted perovskite devices. These HTMs, namely (E)‐4,4'‐(ethene‐1,2‐diylbis(thiophene‐5,2‐diyl))bis(N,N‐bis(4‐methoxyphenyl)aniline) (TPA‐TVT‐TPA) and 4,4'‐(naphthalene‐2,6‐diyl)bis(N,N‐bis(4‐methoxyphenyl)aniline) (TPA‐NAP‐TPA), are designed by using triphenylamine methoxy as common end capping groups with thienylvinylenethienyl and naphthalene cores respectively. They possess good solubility in common organic solvents. Additionally, they have not only appropriate highest occupied molecular orbital energy levels for good hole injection ability but also sufficient lowest unoccupied molecular orbital for electron blocking capability. The power conversion efficiency (PCE) of these HTMs based devices is found to be of 16.32% for TPA‐TVT‐TPA and 14.63% for TPA‐NAP‐TPA. Particularly, TPA‐TVT‐TPA exhibits an impressive Voc of 1.07 V. The obtained performance is one of the highest performances in inverted perovskite layouts. The cut‐price and straightforward synthesis with elegant scale up makes these classes of materials important for the industry to produce high‐throughput printed perovskite solar cells for large area applications.

There has been a stringent demand for blue ($450 to 470 nm) absorbing and red ($611 nm) emitting material systems in phosphor converted white light emitting diodes (WLEDs) available in the market. The conventionally used red-emitting Y 2 O 3 :Eu 3+ phosphor has negligible absorption for blue light produced by GaInN based LED chips. To address this issue, a new red-emitting Gd 2 CaZnO 5 :Eu 3+ (GCZO:Eu 3+) nanophosphor system having exceptionally strong absorption for blue ($465 nm) and significant red ($611 nm) photoluminescence is presented. This is attributed to a dominant f–f transition (5 D 0 / 7 F 2) of Eu 3+ ions, arising due to an efficient energy transfer from the Gd 3+ sites of the host lattice to Eu 3+ ions. The external quantum yield (QY) measured at 465 nm absorption and 611 nm emission revealed that the GCZO:Eu 3+ nanophosphor has better QY of 23% as compared to commercial Y 2 O 3 :Eu 3+ , which is <1%. X-ray diffraction and microscopy observations showed the nanocrystalline nature and slightly elongated morphology of the sample, respectively. While the energy dispersive X-ray analysis identified the chemical constituents of the GCZO:Eu 3+ nanophosphor, the color overlay imaging confirmed the substitution of Eu 3+ for Gd 3+ ions. As seen from the QY statistics it is highly anticipated that the multifold absorption at $465 nm would certainly improve the color rendering properties of existing WLEDs.

Methylammonium lead iodide perovskite solar cells (PSCs) based on a solution-processed ZnO electron transporting layer were systematically investigated at low-temperature operating conditions. The power conversion efficiency gradually improved from 14.2% to 15.5% as the temperature decreased from 298 to 253 K, mainly owing to increments of short circuit current density and open circuit voltage. In addition, the improvements in photocurrent related to the high charge carrier mobility, owing to the ideal non-dispersive charge transport and fast electron transport lifetime at low temperature. Strikingly, hysteresis was suppressed with decreasing temperature related to the inhibition or relatively slow of ionic migration at reversed poling direction. This finding shows promising result of PSCs working efficiently under low temperature condition.

Transition metal perovskite chalcogenides are attractive solar absorber materials for renewable energy applications. Herein, we present the first-principles screened hybrid density functional theory analyses of the structural, elastic, electronic and optical properties of the two structure modifications of strontium zirconium sulfide (needle-like α-SrZrS3 and distorted β-SrZrS3 phases). Through the analysis of the predicted electronic structures, we show that both α-and β-SrZrS3 materials are direct band gaps absorbers, with calculated band gaps of 1.38, and 1.95 eV, respectively, in close agreement with estimates from diffuse-reflectance measurements. A strong light absorption in the visible region is predicted for the α-and β-SrZrS3, as reflected in their high optical absorbance (in the order of 10 5 cm −1), with the β-SrZrS3 phase showing stronger absorption than the α-SrZrS3 phase. We also report the first theoretical prediction of effective masses of photo-generated charge carriers in α-and β-SrZrS3 materials. Predicted small effective masses of holes and electrons at the valence, and conduction bands, respectively, point to high mobility (high conductivity) and low recombination rate of photo-generated charge carriers in α-and β-SrZrS3 materials, which are necessary for efficient photovoltaic conversion.

Charge extraction at carrier transport layers adjacent to
perovskites is crucial for the optimization of perovskite solar cells. In
particular, Sn-perovskites with no lead elements are known to struggle from
charge extraction. Here, we report the effects of organic ligands such as FA
and MA (FA = HC(NH2)2
+; MA = CH3NH3
+) on charge separation at the
interface between electron transport layers and perovskites. TiO2
mesoporous covering the tin-perovskites show significant changes in the
electronic structure and built-in potentials according to the ratio of FA to
MA. Through a local probe with potential and current mapping, charge
transport has been intensively examined. The best cell in this study is
obtained as 5.37% at FA/MA = 3:1 with only iodine at the halide sites.
Even though the value itself is not comparable with lead halides, it could pave a new direction to improve lead-free perovskite
solar cells.

First generation solar panels are based on crystalline silicon and are predominantly rigid.  These panels have been reduced in size and are commercially available to consumers to provide solar energy on the go.  Several second PV technologies are thin enough to conform and bend to irregular topologies associated with backpacks, headbands, and other accessories for greater surface area and increased power generation.  Most third generation PV technologies are also flexible and many are compatible with printing and manufacturing processes that allow solar cells to be integrated directly into fashionable textiles and many forms of clothing including shoes, hats, shirts, shorts, and pants.  Together, the three generations of PV technologies provide multiple options for harvesting both natural and artificial light as part of wearable solar systems and everyday activity.  This chapter looks at the possibilities for powering different wearable solar systems in the quest for a truly literal, zero carbon footprint.

In the past few years, lead halide perovskite solar cell power conversion efficiencies have risen by using a wide variety of fabrication methods and just passed 20%. Perovskite solar cells are typically fabricated in a glovebox to strictly avoid any water exposure. A dry atmosphere significantly increases equipment and operational costs for industrial processes, so ambient perovskite fabrication will be less expensive and more attractive. In this work it is demonstrated that ambient annealing is comparable to annealing in dry N 2 . Perovskite films annealed in a standard dry N 2 environment are compared with those annealed in ambient environment with 50% relative humidity. Solar cell devices were prepared with a planar structure configuration and annealed at one of three different temperatures (105, 115, or 125°C) in either N 2 or ambient air. For all temperatures, the average efficiencies for the devices annealed in air are higher than those annealed in dry N 2 . The highest efficiency achieved for air-annealed devices is 12.7%. Thus, good efficiency cells can be fabricated in an ambient environment, which facilitates mass production.

Organo-metal halide perovskites are an intriguing class of materials that have recently been explored for their potential in solar energy conversion. Within a very short period of intensive research, highly efficient solar cell devices have been demonstrated. One of the heavily debated questions in this new field of research concerns the role of chlorine in solution-processed samples utilizing lead chloride and three equivalents of methylammonium iodide to prepare the perovskite samples. We utilized a combination of X-ray photoelectron spectroscopy, X-ray fluorescence and X-ray diffraction to probe the amount of chlorine in samples before and during annealing. As-deposited samples, before annealing, consist of a crystalline precursor phase containing excess methylammonium and halide. We used insitu techniques to study the crystallization of MAPbI 3 from this crystalline precursor phase. Excess methylammonium and chloride evaporate during annealing forming highly crystalline MAPbI 3 . However, even after prolonged annealing times chlorine can be detected in the films in X-ray fluorescence measurements. 8 and its effect on opto-electronic properties needs to be further investigated to understand the superior solar cell device performance achieved for solution-processed MAPbCl x I 3-x based solar cells.

In CH 3 NH 3 PbI 3-based high efficiency perovskite solar cells (PSCs), tiny amount of PbI 2 impurity was often found with the perovskite crystal. However, for two-step solution process-based perovskite films, most of findings have been based on the films having different morphologies between with and without PbI 2. This was mainly due to the inferior morphology of pure perovskite film without PbI 2 , inevitably produced when the remaining PbI 2 forced to be converted to perovskite, so advantages of pure perovskite photoactive layer without PbI 2 impurity have been overlooked. In this work, we designed a printing-based two-step process, which could not only generate pure perovskite crystal without PbI 2 , but also provide uniform and full surface coverage perovskite film, of which nanoscale morphology was comparable to that prepared by conventional two-step solution process having residual PbI 2. Our results showed that, in two-step solution process-based PSC, pure perovskite had better photon absorption and longer carrier lifetime, leading to superior photocurrent generation with higher power conversion efficiency. Furthermore, this process was further applicable to prepare mixed phase pure perovskite crystal without PbI 2 impurity, and we showed that the additional merits such as extended absorption to longer wavelength, increased carrier lifetime and reduced carrier recombination could be secured. Recently, organometal trihalide perovskite materials having composition ABX 3 (e.g. A = Cs + , CH 3 NH 3 + (meth-ylammonium, MA), or HC(NH 2) 2 + (formamidinium, FA); B = Pb or Sn; X = I, Br or Cl) have been investigated extensively for use as light-absorbing material in solar cells because of their unique properties such as direct optical bandgap, broadband light absorption, bipolar transport, and long carrier diffusion length. Since the first report about perovskite solar cells (PSC) having 3.81% power conversion efficiency (PCE) by Kojima et al. in ref. 1, which triggered intensive research in the development of PSC, remarkable enhancement in power conversion efficiency (PCE) reaching 20% has been achieved during past several years 2–4. In conventional silicon-based p-n junction photovoltaic (PV) devices, the pure crystal structure in photoac-tive layer has been known to be advantageous to efficient charge transport and reduced exciton quenching for high efficiency solar cell. However, in MAPbI 3-based PSC showing high efficiency, tiny amount of residual PbI 2 impurity was often found with the perovskite crystal phase, even though the equimolar composition of organic (MAI) and inorganic (PbI 2) components was utilized to fully convert them to perovskite crystal 3,5–14. Therefore, various approaches have been reported to find out if perovskite crystal with PbI 2 impurity would be advantageous to the performance of PSC or not. However, in general, the crystalline structure and nanoscale morphology of perovskite photoactive layers are significantly influenced by their deposition methodology 15–22 , and therefore those reports should be individually interpreted depending on their growth mechanism. Chen el al. reported an approach to produce pure MAPbI 3 film by treating as-deposited PbI 2 film with MAI vapor for several hours, from which PbI 2 component could be reversibly regenerated when annealed at 150 °C 5,6. They showed that the regenerated PbI 2 from the pure MAPbI 3 crystal structure by annealing was helpful to pas-sivate grain boundary (GB) between crystal domains, consequently improving their device performances due to the reduced recombination 6. Similarly, Zhang et al. investigated the role of PbI 2 in their perovskite film, grown by spin-casting hydrohalide deficient PbI 2 ·xHI (x = 0.9~1) precursor under MA vapor atmosphere. Using their

We report a mechanistic understanding of a moisture-driven intermediate-phase transition that improves the quality of perovskite thin films based on a lead-acetate precursor, improving the power-conversion efficiency. We clarify the composition of the intermediate phase and attribute the transition of this phase to the hygroscopic nature of the organic product, i.e., methylammonium acetate. Thermal annealing aids in the coarsening of the grains. These decoupled processes result in better crystal formation with a lower spatial and energetic distribution of traps. Thermal annealing of the films without exposure to air results in a faster intermediate-phase transition and grain coarsening, which occur simultaneously, leading to disorder in the films and a higher deep trap-state density. Our results indicate the need for a humid environment for the growth of high-quality perovskite films and provide insight into intermediate-phase dissociation and conversion kinetics. Thus, they are useful for the large-scale production of efficient solution-processed perovskite solar cells.

We report on both the intrinsic and the extrinsic stability of a formamidinium lead bromide [CH(NH 2) 2 PbBr 3 = FAPbBr 3 ] perovskite solar cell that yields a high photovoltage. The fabrication of FAPbBr 3 devices, displaying an outstanding photo-voltage of 1.53 V and a power conversion efficiency of over 8%, was realized by modifying the mesoporous TiO 2 −FAPbBr 3 interface using lithium treatment. Reasons for improved photovoltaic performance were revealed by a combination of techniques, including photothermal deflection absorption spectroscopy (PDS), transient-photovoltage and charge-extraction analysis, and time-integrated and time-resolved photoluminescence. With lithium-treated TiO 2 films, PDS reveals that the TiO 2 −FAPbBr 3 interface exhibits low energetic disorder, and the emission dynamics showed that electron injection from the conduction band of FAPbBr 3 into that of mesoporous TiO 2 is faster than for the untreated scaffold. Moreover, compared to the device with pristine TiO 2 , the charge carrier recombination rate within a device based on lithium-treated TiO 2 film is 1 order of magnitude lower. Importantly, the operational stability of perovskites solar cells examined at a maximum power point revealed that the FAPbBr 3 material is intrinsically (under nitrogen) as well as extrinsically (in ambient conditions) stable, as the unsealed devices retained over 95% of the initial efficiency under continuous full sun illumination for 150 h in nitrogen and dry air and 80% in 60% relative humidity (T = ∼60 °C). The demonstration of high photovoltage, a record for FAPbBr 3 , together with robust stability renders our work of practical significance.

A depth behavioral understanding for each layer in perovskite solar cells (PSCs) and their interfacial interactions as a whole has emerged for further enhancement in power conversion efficiency (PCE). Herein, NiO@Carbon was not only simulated as a hole transport layer but also as a counter electrode at the same time in the planar heterojunction based PSCs with the program wxAMPS (analysis of microelectronic and photonic structures)-1D. Simulation results revealed a high dependence of PCE on the effect of band offset between hole transport material (HTM) and perovskite layers. Meanwhile, the valence band offset of NiO-HTM was optimized to be 0.1 to 0.3 eV lower than that of the perovskite layer. Additionally, a barrier cliff was identified to significantly influence the hole extraction at the HTM/absorber interface. Conversely, the band offset
between the active material and NiO@Carbon-HTM was derived to be 0.15 to 0.15 eV with an enhanced efficiency from 15% to 16%.

We discovered that an alcohol soluble non-fullerene small molecule perylene diimides derivative (PDIN), which is a traditional cathode interface material, can be used as a promising electron transporting material for efficient p-i-n perovskite solar cells. Surprisingly, by using 2,2,2-Trifluoroethanol as solvent for PDIN, it can easily form high quality PDIN thin film onto the perovskite layer and overcome the erosion problem of conventional alcohol solvents such as methanol and ethanol etc. In addition, PDIN can efficiently quench the photoluminescence of perovskite layer and extract electrons from perovskite layer. Finally, a power conversion efficiency of 15.28% is achieved from the device with PDIN as electron transporting layer, which is significantly higher than the PC61BM only device. Further, we also found that the performance of the device with PDIN as electron transporting layer is not sensitive to the PDIN's thickness. These results indicate that PDIN is a promising electron transporting material for efficient p-i-n perovskite solar cells.

The past few years have witnessed remarkable progress in solution processed methyl ammonium lead halide (CH3NH3PbX3, X = halide) perovskite solar cells with reported photoconversion efficiency () exceeding 20% in laboratory scale devices and up to 13% in their large area modules (PSMs). These devices mostly employ mesoporous TiO2 nanoparticles as an electron transport layer (ETL) which furnishes a scaffold for the perovskite semiconductor to grow. However, limitations due to trap-limited electron transport and non-complete pore filling exist. Herein, we have employed TiO2 nanorods (NRs), a material offering a two-fold higher electronic mobility and higher pore-filing compared to their particle analogues, as an ETL. A crucial issue in NRs patterning over substrates is resolved using precise Nd:YVO4 laser ablation, and a champion device with  ~8.1% is reported via a simple and low cost vacuum-vapor assisted sequential processing (V-VASP) of CH3NH3PbI3 film. Our experiments showed a successful demonstration of NRs based PSMs via V-VASP technique which can be applied to fabricate large area modules with a pinhole-free, smooth and dense perovskite layer required to build high efficiency devices.

Toxicity as well as chemical instability issues of halide perovskites based on organic-inorganic lead-containing materials still remains the main drawbacks for perovskite solar cells (PSCs). Herein, we discuss the preparation of copper (Cu)-based hybrid materials, where we replace lead (Pb) with non-toxic Cu metal for lead free perovskite solar cells; investigate of its potential towards solar cells applications based on experimental and theoretical studies. The formation of (CH3NH3)2CuX4 [(CH3NH3)2CuCl4, (CH3NH3)2CuCl2I2, and (CH3NH3)2CuCl2Br2] were discussed in details. Furthermore, founding chlorine (Cl-) in the structure is critical for the stabilization of the formed compounds. Cu-based perovskite-like materials illustrated attractive absorbance features extended to the near-infrared, with appropriate band gaps. Green photoluminescence of these materials obtained due to Cu+ ions. The power conversion efficiency (PCE) measured experimentally and estimated theoretically for diffe...

Highly crystalline nanostructured nickel(II) oxide microballs (NiO-mBs) were developed for use in p-type dye-sensitized solar cells (p-DSC). Their high specific surface area and favorable optical properties yielded unprecedented photocurrent densities of 7.0 mA cm À2 under simulated sunlight (AM1.5; 1000 W m À2 ) and incident photon to charge carrier conversion efficiencies of 74% when applied in p-DSCs. This is an important step towards matching the performance of p-DSCs with their n-type counterparts for future tandem applications.

Perovskite based solar cells have attracted much recent research interest due to the large efficiencies reported for simple planar structures. However, there is a lack of clarity in literature on the key functional parameters that control the eventual efficiencies. In this article, we provide a comprehensive modeling framework, well calibrated with experimental results from literature, to understand/interpret Perovskite based solar cells and suggest further optimization schemes. Indeed, our results show that the dark and light characteristics of these devices are dominated by recombination in Perovskite layer. Curiously, our analytical model predicts that the open circuit voltage could be much larger than built-in potential, a result supported by both literature results and numerical simulations. Finally, we identify optimization pathways to achieve > 20% efficiency for such solar cells.

In the last few years, research on dye-sensitised devices has been focused on the development of solar cells, based on CH 3 NH 3 PbX 3 (X = I − , Br − , Cl −) composites with perovskite structure. The deposition of perovskite thin films is usually carried out by solution-based processes using spin-coating techniques that result in the production of high quality films. Solar cells made by this method exceed 20% efficiency, with the potential for use in large scale production through ink print or screen printing techniques. As an alternative route, perovskite thin films can be deposited through thermal evaporation. A new method is proposed to produce CH 3 NH 3 PbI 3 , based on a radio-frequency (rf)-sputtering technique that results in a high reproducibility of the films and is compatible with roll-to-roll processes. We deposited thin films of lead-sulphide (PbS) and converted them into perovskite by placing the films in an iodine atmosphere, followed by dipping in a solution of methylammonium iodide (CH 3 NH 3 I). The conversions to PbI 2 and CH 3 NH 3 PbI 3 were confirmed by elemental analyses, absorption, and photoluminescence spectroscopy. Structural properties were revealed by X-ray diffraction and infrared and Raman spectroscopy.

Despite spectacular advances in conversion efficiency of perovskite solar cell many aspects of its operating modes are still poorly understood. Capacitance constitutes a key parameter to explore which mechanisms control particular functioning and undesired effects as current hysteresis. Analyzing capacitive responses allows addressing not only the nature of charge distribution in the device but also the kinetics of the charging processes and how they alter the solar cell current. Two main polarization processes are identified. Dielectric properties of the microscopic dipolar units through the orthorhombic-to-tetragonal phase transition account for the measured intermediate frequency capacitance. Electrode polarization caused by interfacial effects, presumably related to kinetically slow ions piled up in the vicinity of the outer interfaces, consistently explain the reported excess capacitance values at low frequencies. In addition, current−voltage curves and capacitive responses of perovskite-based solar cels are connected. The observed hysteretic effect in the dark current originates from the slow capacitive mechanisms.

Micron-sized macroporous TiO2 spheres (MAC-TiO2) were synthesized using a colloidal templating process inside emulsions, which were then coated on a nanocrystalline TiO2 light absorption film to prepare a bilayered photoanode for liquid-based dye-sensitized solar cells (DSSC) and hybrid heterojunction solid-state solar cells. MAC-TiO2 layers can  enhance light scattering as well as absorption, because their pore size and periodicity are comparable to light wavelength for unique multiple scattering and a porous surface can load dye more. Moreover, due to the bicontinuous nature of macropores and TiO2 walls, electrolyte could be transported much faster in between the TiO2 spheres rather than within the small TiO2 nonporous architectures. Electron transport was also facilitated along the interconnected TiO2 walls. In DSSCs with these MAC-TiO2 scattering layers, efficiency was higher  than conventional DSSCs incorporating a commercial scattering layer. The unique geometry of MAC-TiO2results in strong improvements in light scattering and infiltration of  hole-transporting materials, thereby the MAC-TiO2 -based solid-state device showed comparatively higher efficiency than the device with conventional nanocrystalline TiO2

Perovskite solar cell (PSCs) technology has made a tremendous impact in the solar cell community due to the exceptional performance of PSCs as the power conversion efficiency (PCE) surged to a world record of 22% within the last few years. Despite this high efficiency value, the commercialization of PSCs for large area applications at affordable prices is still pending due to the low stability of the devices under ambient atmospheric conditions and the very high cost of the hole transporting materials (HTMs) used as the charge transporting layer in these devices. To cope with these challenges, the use of cheap HTMs can play a dual role in terms of lowering the overall cost of perovskite technology as well as protecting the perovskite layer to achieve a higher stability. To achieve these goals, various new organic hole transporting materials (HTMs) have been proposed. In this study, we used a unique and novel anthanthrone (ANT) dye as a conjugated core building block and an affordable moiety to synthesize a new HTM. The commercially available dye was functionalized with an extended diphenylamine (DPA) end capping group. The newly developed HTM, named DPA-ANT-DPA, was synthesized in a single step and used successfully in mesoporous perovskite solar cell devices, achieving a PCE of 11.5% under 1 Sun condition with impressive stability. The obtained device efficiency is amongst the highest as compared to that of other D-AD molecular design and low band gap devices. This kind of low cost HTM based on an inexpensive starting precursor, anthanthrone dye, paves the way for the economical and large-scale production of stable perovskite solar cells.