Water- and heat-activated dynamic passivation for perovskite photovoltaics.

Further improvements in perovskite solar cells (PSCs) require better control of ionic defects in the perovskite photoactive layer during the manufacturing stage and their usage1-5. Here, we report a living passivation strategy using a hindered urea/thiocarbamate bond6-8 Lewis acid-base material (HUBLA), where dynamic covalent bonds with water and heat-activated characteristics can dynamically heal the perovskite to ensure device performance and stability. Upon exposure to moisture or heat, HUBLA generates new agents and further passivates defects in the perovskite. This passivation strategy achieved high-performance devices with a power conversion efficiency (PCE) of 25.1%. HUBLA devices retained 94% of their initial PCE for approximately 1500 hours of aging at 85 °C in N2 and maintained 88% of their initial PCE after 1000 hours of aging at 85 °C and 30% relative humidity (RH) in air.

Steric Effects on the Photovoltaic Performance of Panchromatic Ruthenium Sensitizers for Dye-Sensitized Solar Cells.

Three new heteroleptic Ru complexes, CYC-B22, CYC-B23C, and CYC-B23T, were prepared as sensitizers for coadsorbent-free, panchromatic, and efficient dye-sensitized solar cells. They are simultaneously functionalized with highly conjugated anchoring and ancillary ligands to explore the electronic and steric effects on their photovoltaic characteristics. The coadsorbent-free device based on CYC-B22 achieved the best power conversion efficiency (PCE) of 8.63% and a panchromatic response extending to 850 nm. The two stereoisomers, CYC-B23C and CYC-B23T coordinated with an unsymmetrical anchoring ligand, display similar absorption properties and the same driving forces for electron injection as well as dye regeneration. Nevertheless, the devices show not only the remarkably distinct PCE (6.64% vs 8.38%) but also discernible stability. The molecular simulation for the two stereoisomers adsorbed on TiO2 clarifies the distinguishable distances (16.9 Å vs 19.0 Å) between the sulfur atoms in the NCS ligands and the surface of the TiO2, dominating the charge recombination dynamics and iodine binding and therefore the PCE and stability of the devices. This study on the steric effects caused by the highly conjugated and unsymmetrical anchoring ligand on the adsorption geometry and photovoltaic performance of the dyes paves a new way for advancing the molecular design of polypyridyl metal complex sensitizers.

Bicyclopentadithiophene-Based Organic Semiconductor for Stable and High-Performance Perovskite Solar Cells Exceeding 22.

Well-performing organic-inorganic halide perovskites are susceptible to poor efficiency and instability due to their various defects at the interphases, grain boundaries (GBs), and surfaces. In this study, an in situ method is utilized for effectively passivating the under-coordinated Pb2+ defects of perovskite with new non-fullerene acceptors (NFAs) (INXBCDT; X = H, Cl, and Br) through their carbonyl and cyano functional groups during the antisolvent dripping process. It reveals that the bicyclopentadithiophene (BCDT) core with highly electron-withdrawing end-capping groups passivates GBs and boosts perovskite grain growth. This effective defect passivation decreases the trap density to increase the carrier recombination lifetime of the perovskite film. As a result, bromo-substituted dicyanomethylene indanone (INBr)-end-capped BCDT (INBrBCDT-b8; 3a)-passivated devices exhibit the highest power conversion efficiency (PCE) of 22.20% (vs those of 18.09% obtained for perovskite films without passivation) upon an optimized film preparation process. Note that devices treated with more soluble 2-ethylhexyl-substituted compounds (1a, 2a, and 3a) exhibit higher PCE than those treated with less soluble octyl-substituted compounds (1b, 2b, and 3b). It is also worth noting that BCDT is a cost-effective six-ring core that is easier to synthesize with a higher yield and therefore much cheaper than those with highly fused-ring cores. In addition, a long-term stability test in a glovebox for 1500 h reveals that the perovskite solar cells (PSCs) based on a perovskite absorber treated with compound 3a maintain ∼90% of their initial PCE. This is the first example of the simplest high-conjugation additive for perovskite film to achieve a PCE greater than 22% of the corresponding lead-based PSCs.

Sol-Gel Prepared Spinel HTLs for Assembling 20% Efficiency Perovskite Solar Cell in Air Without Using Anti-Solvent and Toxic Solvent.

Low-temperature sol-gel prepared ZnCo2 O4 spinel-based thin films are developed as high-performance hole transporting layer (HTL) for coating perovskite film (NA-Psk) from the basic MAPbI3 /ACN/CH3 NH2 solution in air without using anti-solvent. Inverted PSC based on 2 mole% (vs Zn) Cu2+ doped ZnCo2 O4 (2%Cu@ZnCo2 O4 ) HTL and NA-Psk absorber exhibit the maximum power conversion efficiency (PCE) of 20.0% with no current hysteresis while the cell based on ZnCo2 O4 and PEDOT:PSS HTL (using NA-Psk absorber) achieves the PCE of 15.79% and 12.3% with a current hysteresis index of 9.8% and 32.4%, respectively. Without encapsulation, PSCs based on 2%Cu@ZnCo2 O4 , ZnCo2 O4 , and PEDOT:PSS HTLs maintain 90%, 77%, and 12%, respectively of the original efficiency by standing in ambient atmosphere (temperature: 20-25 °C, RH:30%-40%) for 1800 h. Large area (10 cm × 10 cm substrate) perovskite mini-module (PSM) with PCE over 15% is also demonstrated by using sol-gel prepared 2%Cu@ZnCo2 O4 HTL. The poor photovoltaic performance of PEDOT:PSS HTL is due to the basic MAPbI3 /ACN/CH3 NH2 solution will deprotonate the acidic PEDOT:PSS to reduce its conductivity whereas ZnCo2 O4 HTL are not affected by basic perovskite precursor solution.

Large-Area Perovskite Film Prepared by New FFASE Method for Stable Solar Modules Having High Efficiency under Both Outdoor and Indoor Light Harvesting.

High-quality perovskite film is deposited on a 30 cm × 40 cm LiCoO2 -coated ITO/glass via newly developed freely falling anti-solvent extraction (FFASE) method followed by post watervapor annealing in an ambient atmosphere. Perovskite solar modules (PSMs, active area of 25.2 cm2 with mask) based on this high-quality film achieve the highest efficiency of 16.04 and 30.76% under 1 sun (100 mW cm-2 ) and 945 lux fluorescent light illumination, respectively. The encapsulated PSMs are stable at -20 to 80 °C thermal cycling and keep high efficiency at temperature as low as -20 °C and as high as 80 °C. When the encapsulated PSM is heated at 85 °C and 85% relative humidity under room lighting or heated at 60 °C under AM1.5 (100 mW cm-2 ) illumination for 1000 h, loses only ≈8% of its original efficiency. The high stability of PSMs is due to very high quality perovskite absorber being used. The underlying concept of the FFASE method for extracting the solvent from the large-area perovskite precursor film is that the whole precursor film contacts with the fresh anti-solvent during the crystallization stage.

Multifunctional Ionic Fullerene Additive for Synergistic Boundary and Defect Healing of Tin Perovskite to Achieve High-Efficiency Solar Cells.

A series of new ionic fullerene derivatives (C60-RNH3-X; X = Cl, Br, or I) were designed especially for using as additives for tin perosvkite (TPsk, with chemical formula of FA0.98EDA0.01SnI3) to form TPsk-C60-RNH3-X bulk heterojunction (BHJ) films. Inverted tin-perovskite solar cells (TPSCs) based on BHJ TPsk-C60-RNH3-Br absorber achieved the highest power conversion efficiency up to 11.74% with very high FF of 73%, without current hysteresis and stable in a glovebox. The designed spherical ionic fullerene halide additive, sitting in the grain boundaries of the TPsk film, can not only improve the quality of the TPsk film and change the valence band energy to match better with the PEDOT:PSS hole transporter but also be a carrier transporting connector between tin-perovskite grains, the defects/traps passivation/healing agent by interacting with Sn2+ ions and filling the halogen vacancies. The functions of the ionic fullerene halide additive were revealed with XRD patterns, SEM images, element mapping, UPS spectra, infrared spectra, AFM, and SCLC data. Being able to passivate newly generated defects during device operation or sitting on the shelf is an important step to improve the long-term stability of TPSCs. If a passivation agent can move dynamically during cell operation or storage to heal the defects of perovskite, the instability problem of TPSCs can be alleviated. The spherical ionic fullerene halide could be one of the ideal passivation agents satisfying this purpose.

Synergistic Engineering of the Conductivity and Surface Properties of PEDOT:PSS-Based HTLs for Inverted Tin Perovskite Solar Cells to Achieve Efficiency over 10.

A new simple environmentally benign water-soluble zwitterion, sulfamic acid (SA), was used as a multifunctional additive to tune the properties of PEDOT:PSS-based hole transporting layer (HTL). A layer of PEDOT:PSS was inserted in-between the ITO electrode and SA-modified PEDOT:PSS to form a pseudo bi-layered PS/SA@PS HTL to protect the ITO electrode from damage by more acidic SA@PS. Inverted tin-based perovskite solar cells based on the pseudo bi-layered PS/SA@PS HTLs achieved the highest efficiency of 10.5% with very small current hysteresis. The cell lost only 5% of the initial efficiency by storing in a glovebox without packing for more than 2000 h. The functions of SA include increasing the conductivity and mobility of the HTL to extract and transport the hole facilely by changing the conformation of PEDOT chains via zwitterion-induced charge screening, elevating the work function of PEDOT:PSS to match the VB of TPsk via increasing the PSS- chains on the HTL surface, creating a more hydrophilic surface for depositing better quality tin perovskite film (TPsk with the chemical formula of FA0.98EDA0.01SnI3), and avoiding the oxidation Sn2+ to Sn4+ via interacting with Sn2+ ions (at the HTL/absorber interface) using the sulfite group on SA, which were revealed with various physicochemical data.

The function of Chalcogenophene in the Cyclomatelated Ring of the Cycloruthenated Dyes applied in Dye-Sensitized Solar Cell.

Three thiocyanate-free cycloruthenated complexes, DUY24-O, DUY24, and DUY24-Se containing furan, thiophene, and selenophene, respectively, as a part of the cycloruthenated ring, were designed to reveal the function of the chalcogen atom on the physicochemical and photovoltaic performance of the cycloruthenated sensitizers applied in dye-sensitized solar cells (DSCs). The three sensitizers have a similar molecular size; therefore, the effect of molecular dimensions on their photovoltaic performance can be negligible. NMR data, electron-donating resonance effects, optical properties, and the energy levels of the frontier orbitals reveal that the physical/photovoltaic properties of the three sensitizers were affected significantly by the chalcogen atom on the cyclometalated chalcogenophene ring. The λmax (both in ethanol and adsorbed on TiO2), frontier orbital level, and dye loading of thiophene- and selenophene-containing dyes are very close. Nevertheless, DUY24-Se has a higher molar absorption coefficient compared to DUY24; therefore, the DSC based on DUY24-Se has higher efficiency (8.4% under AM1.5 G one-sun and 26% under T5-light at ca. 6000 lux) than that sensitized with the DUY24 dye. These efficiencies are also higher than those (7.9 and 21.6%, respectively) of the cell dyed with N719, fabricated using the same conditions. The better performance of the device sensitized with DUY24-Se compared to DUY24-based cells suggests that selenophene is as good as (or even better than) thiophene to be a part of the cyclometalated ring for thiocyanate-free cycloruthenated sensitizers applied in DSCs. Furan-containing DUY24-O has much worse photovoltaic performance compared to the other two dyes. This is not only because DUY24-O has the shortest λmax, the lowest molar absorption coefficient, and the highest HOMO level but also the lowest dye loading (because of the strong interaction between the oxygen in furan and TiO2, the array of DUY24-O occupies more surface when adsorbed on TiO2) and the fastest charge recombination. The physicochemical and photovoltaic properties as well as the adsorption behavior of the dye on the TiO2 anode for the cycloruthenated sensitizers affected significantly by the chalcogen atom of the chalcogenophene on the cyclometalated ring provide a new strategy to design high-efficiency NCS-free cyclometalated sensitizers for DSCs.

Synergistic Engineering of Conduction Band, Conductivity, and Interface of Bilayered Electron Transport Layers with Scalable TiO2 and SnO2 Nanoparticles for High-Efficiency Stable Perovskite Solar Cells.

A simple, synergistic engineering of the conduction band (CB), conductivity, and interface of TiO2-based bilayered electron transport layers (ETLs) via scalable TiO2 and SnO2 nanoparticles processed at low temperature (≤ 100 °C) for regular planar perovskite solar cells (PSCs) was developed. The bottom layer (Lt-TiO2:SnO2 nanocomposite film) was prepared by spin coating from the ethanol suspension of small ground TiO2 nanoparticles with big ground SnO2 nanoparticles as the additive. The top C-SnO2 layer (spin-coated from the concentrated commercial SnO2 nanoparticles (C-SnO2 NPs, 20 wt %, 7 nm in size suspended in H2O)) can be regarded as an interlayer between Lt-TiO2:SnO2 and perovskite (Psk) absorbers. Bilayered Lt-TiO2:SnO2/C-SnO2 ETLs are dense films with a cascade CB, good conductivity, facile electron extraction/transport ability, and a highly hydrophilic surface for depositing high-quality Psk films. Regular planar PSCs based on Lt-TiO2:SnO2/C-SnO2 ETLs combined with a (FAI)0.90(PbI2)0.94(MABr)0.10(PbBr2)0.10 absorber and a spiro-OMeTAD hole transporter achieved the highest power conversion efficiency of 22.04% with a negligible current hysteresis. The champion cell lost less than 3% of the initial efficiency under continuous room lighting (1000 lux) for 1000 h (lost 10% after 2184 h) without encapsulation under an inert atmosphere. Four related low-temperature-processed ETLs (Lt-TiO2/C-SnO2, Lt-C-SnO2, Lt-TiO2:SnO2, and Lt-TiO2) were fabricated using the same metal oxide nanoparticle suspensions and studied simultaneously to reveal the function of each metal oxide in the bilayered Lt-TiO2:SnO2/C-SnO2 ETLs. In the bottom Lt-TiO2:SnO2 layer, small TiO2 nanoparticles were needed for making a dense film, and highly conducting big SnO2 nanoparticles are used to increase the conductivity of ETLs and a handy electron transport path for reducing the charge accumulation and series resistance of the cell. A top C-SnO2 layer (regarded as an interlayer between Psk and Lt-TiO2:SnO2) was used to extract/transport electrons facilely, to form a bilayered ETL with a cascade CB, and to create a hydrophilic surface to deposit high-quality Psk films to enhance the photovoltaic performance of the PSCs. This study provides a blueprint for designing good-performance ETLs for high-efficiency, stable regular planar PSCs using various sized nanoparticles prepared in a very simple and low-cost way.

Function of Tetrabutylammonium on High-Efficiency Ruthenium Sensitizers for Both Outdoor and Indoor DSC Application.

The function of tetrabutyl ammonium ions (TBA+) in a sensitizer used in dye-sensitized solar cells (DSC) is contradictory. TBA+ can reduce unwanted charge-recombination by protecting the TiO2 surface and reduce dye aggregation, enhancing the photovoltaic performance. It will also compete with the dye-loading on the TiO2 film, decreasing the short-circuit current density of the cell. Three ruthenium sensitizers (DYE III, DUY11, and DUY12 containing two H+, one H+/one TBA+, and two TBA+, respectively) were prepared to systematically investigate the function of TBA+ in a dye for DSC under both standard sunlight and indoor illumination. The optical properties and frontier orbital energy level of the sensitizers are not influenced significantly by the number of TBA+. Under the standard 1 sun illumination, DSCs based on DUY11 (containing one H+ and one TBA+) achieved the highest power conversion efficiency (PCE) of 11.47%. Overall, optimized DSCs sensitized by the three ruthenium dyes all have the PCE over 10%, which is higher than that (9.95%) of N719-dyed cell fabricated at the same conditions. Under the illumination of a light emitting diode (LED), DSCs sensitized by DUY11 also have the highest efficiency of 19%. Furthermore, DUY12 with two TBA+ exhibits superior photovoltaic performance compared to a DYE III (containing two H+ in the anchoring ligands)-dyed cell; although these two dyes have similar photovoltaic performance under standard 1 sun lighting. The important function of TBA+ in reducing the charge recombination (by protecting TiO2 surface and avoiding dye aggregation) of a DSC under indoor lighting (when small number of electrons were excited by weak light) is also revealed.

Scalable Ultrasonic Spray-Processing Technique for Manufacturing Large-Area CH3NH3PbI3 Perovskite Solar Cells.

Organic-inorganic hybrid perovskite solar cells are on the brink of a breakthrough in photovoltaic technology. Scale-up and large-area processing have become the focal points that must be resolved before commercialization. In this study, the scalable ultrasonic spray deposition method for high-throughput coating of the perovskite photoactive layer with a large active area of up to 3 cm2 is implemented by precisely controlling the concentration of the precursor solution and spray passes. CH3NH3PbI3 films with large crystallites and a suitable thickness of ∼350 nm are facilely developed through one-step direct ultrasonic spraying. Less hysteresis and highly reproducible power conversion efficiencies (PCEs) of up to 12.30% (11.43 ± 0.43% on average for 20 devices) are achieved by an optimized single-junction device with an active area of 1 cm2, along with good ambient stability. The device retained ∼80 and ∼65% of the initial PCE after 60 and 105 days in ambient, respectively. The ultrasonic spray-coated perovskite solar cells can be further scaled to larger areas of 2 and 3 cm2 and exhibit PCEs of 10.18 and 7.01%, respectively. The reliable scale-up process for manufacturing the atmospheric wet-coated perovskite film is available in cost-effective and easily operated bench-top variants to bridge the interconnection between applied research and industry.

A Method for the Preparation of Highly Oriented MAPbI3 Crystallites for High-Efficiency Perovskite Solar Cells to Achieve an 86% Fill Factor.

The quality of the perovskite absorber is known to be the most crucial parameter for the photovoltaic performance of perovskite solar cells. By combining the one-step anti-solvent engineering method followed by gas blowing, MAPbI3 film containing highly oriented multi-crystalline nanograins (150∼500 nm) was made first. A user-friendly, simple, large-throughput, and reproducible post-solvent annealing (made by treating the film with anti-solvent containing H2O under spinning) was used to enlarge the perovskite grains up to 1.5 µm. Inverted (p-i-n) perovskite solar cells based on this highly ordered, large-grain MAPbI3 film achieve the highest efficiency of 21% with an extremely high fill factor (FF) of 86%. The high-efficiency cell shows almost no current hysteresis and is stable under 1 sun illustration in a glovebox or standing in the ambient atmosphere (20∼25 °C, ca. 30% humidity) under room lighting (T5 lamp, 500 lux). A creative method combining the gas blowing with quick and simple post-treatment to prepare a highly oriented MAPbI3 film with large multi-crystalline grains to achieve excellent photovoltaic performance was demonstrated. This creative film-preparation method was also successfully applied to fabricate large area MAPbI3 film for high-efficiency perovskite mini-modules. Being able to control the crystallization and growth of perovskite crystallites definitely makes the fabrication of perovskite solar cells more reproducible.

Functional graded fullerene derivatives for improving the fill factor and device stability of inverted-type perovskite solar cells.

A graded fullerene derivative thin film was used as a dual-functional electron transport layer (ETL) in CH3NH3PbI3 (MAPbI3) solar cells, to improve the fill factor (FF) and device stability. The graded ETL was made by mixing phenyl-C61-butyric acid methyl ester (PCBM) molecules and C60-diphenylmethanofullerene-oligoether (C60-DPM-OE) molecules using the spin-coating method. The formation of the graded ETLs can be due to the phase separation between hydrophobic PCBM and hydrophilic C60-DPM-OE, which was confirmed by XPS depth-profile analysis and an electron energy-loss spectroscope. Comprehensive studies were carried out to explore the characteristics of the graded ETLs in MAPbI3 solar cells, including the surface properties, electronic energy levels, molecular packing properties and energy transfer dynamics. The elimination of the s-shape in the current density-voltage curves results in an increase in the FF, which originates from the smooth contact between the C60-DPM-OE and hydrophilic MAPbI3 and the formation of the more ordered ETL. There was an improvement in device stability mainly due to the decrease in the photothermal induced morphology change of the graded ETLs fabricated from two fullerene derivatives with distinct hydrophilicity. Consequently, such a graded ETL provides dual-functional capabilities for the realization of stable high-performance MAPbI3 solar cells.

S,N-Heteroacene-Based Copolymers for Highly Efficient Organic Field Effect Transistors and Organic Solar Cells: Critical Impact of Aromatic Subunits in the Ladder π-System.

Three novel donor-acceptor alternating polymers containing ladder-type pentacyclic heteroacenes (PBo, PBi, and PT) are synthesized, characterized, and further applied to organic field effect transistors (OFETs) and polymer solar cells. Significant aspects of quinoidal characters, electrochemical properties, optical absorption, frontier orbitals, backbone coplanarity, molecular orientation, charge carrier mobilities, morphology discrepancies, and the corresponding device performances are notably different with various heteroarenes. PT exhibits a stronger quinoidal mesomeric structure, linear and coplanar conformation, smooth surface morphology, and better bimodal crystalline structures, which is beneficial to extend the π-conjugation and promotes charge transport via 3-D transport pathways and in consequence improves overall device performances. Organic photovoltaics based on the PT polymer achieve a power conversion efficiency of 6.04% along with a high short-circuit current density (JSC) of 14.68 mA cm-2, and a high hole mobility of 0.1 cm2 V-1 s-1 is fulfilled in an OFET, which is superior to those of its counterparts, PBi and PBo.

High-Efficiency Cycloruthenated Sensitizers for Dye-Sensitized Solar Cells.

Four thiocyanate-free ruthenium sensitizers (DUY24-DUY27) containing 2-thienylpyridine moiety as cyclometalating core were synthesized for dye-sensitized solar cell (DSC) application. To the best of our knowledge, DUY24-DUY27 are four best-efficiency sensitizers having 42%-65% higher efficiencies compared to those of the published sensitizers comprising the same type of the cyclometalating ancillary ligands. The significant characteristic of DUY24-DUY27 is their ß-lowest unoccupied spin orbital (ß-LUSO) distributes remarkably on the cyclometalating ligands, especially on the soft sulfur atom, which strengthens the interaction between the oxidized dye and iodide ion for efficient dye regeneration. The photovoltaic performance of DUY24-DUY27-based DSCs supports that the dye regeneration (therefore the short-circuit photocurrent density (JSC) of the cell) can be improved by not only lowering the highest occupied molecular orbital energy level of the dye molecule but also distributing the ß-LUSO properly on the soft atoms. The study provides an important new guide for designing high-efficiency ruthenium-based dyes for DSC application.

Performance Characterization of Dye-Sensitized Photovoltaics under Indoor Lighting.

Indoor utilization of emerging photovoltaics is promising; however, efficiency characterization under room lighting is challenging. We report the first round-robin interlaboratory study of performance measurement for dye-sensitized photovoltaics (cells and mini-modules) and one silicon solar cell under a fluorescent dim light. Among 15 research groups, the relative deviation in power conversion efficiency (PCE) of the samples reaches an unprecedented 152%. On the basis of the comprehensive results, the gap between photometry and radiometry measurements and the response of devices to the dim illumination are identified as critical obstacles to the correct PCE. Therefore, we use an illuminometer as a prime standard with a spectroradiometer to quantify the intensity of indoor lighting and adopt the reverse-biased current-voltage (I-V) characteristics as an indicator to qualify the I-V sampling time for dye-sensitized photovoltaics. The recommendations can brighten the prospects of emerging photovoltaics for indoor applications.

Effect of the CF3 Substituents on the Charge-Transfer Kinetics of High-Efficiency Cyclometalated Ruthenium Sensitizers.

Six thiocyanate-free complexes, DUY1-DUY6, were synthesized, and their application in a dye-sensitized solar cell was studied to explore the effect of the CF3 substituent positioned in the ancillary ligand and the structure of the anchoring ligand on the physicochemical properties, charge-transfer kinetics, and photovoltaic properties of ruthenium sensitizers. When the electron-withdrawing groups were installed on the cyclometalating ligands and their π conjugation of the ancillary ligand was extended, the frontier orbital energy levels of the ruthenium complex appeared to be sufficient for effective electron injection and dye regeneration, at the same time having high light-harvesting ability. Two electron-withdrawing CF3 groups meta to the cyclometalated position reduce the electron density at the metal center less seriously than o-CF3 and p-CF3 groups. The sensitizers containing a m-CF3 group also reveal a more favorable distribution of ß lowest unoccupied spin orbital for interaction between the oxidized dyes and the iodide ion, which promotes dye regeneration. The absorption profiles of DUY1-DUY4 adsorbed a TiO2 film extended to longer wavelength compared to those in an N,N-dimethylformamide solution, especially DUY1 and DUY2 dyes, which have λmax red shifts of up to 30 nm. The DUY2-dyed cell exhibited the highest efficiency of 9.03%, while the power conversion efficiencies of DUY1-, DUY3-, DUY4-, and N719-based devices were 7.40%, 7.01%, 8.92%, and 8.63%, respectively. DUY5 and DUY6 (the side products of DUY3 and DUY4) without anchoring groups have very weak physical adsorption on a TiO2 anode. The corresponding cells exhibit very low efficiency (<0.1%), although both dyes have high light-harvesting ability and proper frontier orbital energy levels.

Film Grain-Size Related Long-Term Stability of Inverted Perovskite Solar Cells.

The power conversion efficiency (PCE) of the perovskite solar cell is high enough to be commercially viable. The next important issue is the stability of the device. This article discusses the effect of the perovskite grain-size on the long-term stability of inverted perovskite solar cells. Perovskite films composed of various sizes of grains were prepared by controlling the solvent annealing time. The grain-size related stability of the inverted cells was investigated both in ambient atmosphere at relative humidity of approximately 30-40 % and in a nitrogen filled glove box (H2 O<0.1 ppm, O2 <10 ppm). The PCE of the solar cell based on a perovskite film having the grain size larger than 1 µm (D-10) decreases less than 10 % with storage in a glove box and less than 15 % when it was stored under an ambient atmosphere for 30 days. However, the cell using the perovskite film composed of small (∼100 nm) perovskite grains (D-0) exhibits complete loss of PCE after storage under the ambient atmosphere for only 15 days and a PCE loss of up to 70 % with storage in the glove box for 30 days. These results suggest that, even under H2 O-free conditions, the chemical- and thermal-induced production of pin holes at the grain boundaries of the perovskite film could be the reason for long-term instability of inverted perovskite solar cells.

Nano-structured CuO-Cu2O Complex Thin Film for Application in CH3NH3PbI3 Perovskite Solar Cells.

Nano-structured CuO-Cu2O complex thin film-based perovskite solar cells were fabricated on an indium tin oxide (ITO)-coated glass and studied. Copper (Cu) thin films with a purity of 99.995 % were deposited on an ITO-coated glass by magnetron reactive sputtering. To optimize the properties of the nano-structured CuO-Cu2O complex thin films, the deposited Cu thin films were thermally oxidized at various temperatures from 300 to 400 °C. A CH3NH3PbI3 perovskite absorber was fabricated on top of CuO-Cu2O complex thin film by a one-step spin-coating process with a toluene washing treatment. Following optimization, the maximum power conversion efficiency (PCE) exceeded 8.1 %. Therefore, the low-cost, solution-processed, stable nano-structured CuO-Cu2O complex thin film can be used as an alternative hole transport layer (HTL) in industrially produced perovskite solar cells.

A perovskite cell with a record-high-V(oc) of 1.61 V based on solvent annealed CH3NH3PbBr3/ICBA active layer.

A high open-circuit voltage inverted perovskite solar cell based on a CH3NH3PbBr3 absorber and ICBA acceptor is reported. The CH3NH3PbBr3 film fabricated under ambient atmosphere at a moderate temperature (∼100 °C) using a two-step spin-coating method is composed of aggregated nano-grains. Upon solvent annealing of the CH3NH3PbBr3/ICBA film, the efficiency of the resulting cell increases from 1.71% to 7.50% with a remarkably high open circuit voltage (Voc) of ca. 1.60 V. ICBA acts not only as a high LUMO acceptor to realize high Voc but also as a mending agent to increase the efficiency of the cell by penetrating into the defects/voids of the CH3NH3PbBr3 film via solvent annealing as evidenced by TRPL, XPS and SEM data. Solvent annealing of the active layer was proved to be simple and effective device engineering to improve the efficiency of the perovskite cell based on a low quality film and the Voc of the inverted perovskite cell can be tuned by the LUMO level of the acceptor were revealed. The CH3NH3PbBr3/ICBA film is semi-transparent with an average 50% transmittance under visible light. The moderatetemperature processed CH3NH3PbBr3 solar cell with high Voc and a semi-transparent absorber has great potential for application as the top cell in a tandem solar cell.