Performance enhancement of perovskite solar cells: surface is the key

<正>Metal halide perovskite solar cells (PSCs) stand out as one of the most promising contenders among photovoltaic technologies for the future. Over the past decade, PSCs with high power conversion efficiency (PCE) predominantly adopted the normal (ni-p) device structure. However, a common p-type organic small molecule, Spiro-OMe TAD, which is widely employed at the top layer of n-i-p devices [1], faces issues such as susceptibility to water absorption and poor thermal stability.     

Solution-processed MoO₃ thin films as a hole-injection layer for organic solar cells

We report on a sol-gel-based technique to fabricate MoO(3) thin films as a hole-injection layer for solution-processed or thermally evaporated organic solar cells. The solution-processed MoO(3) (sMoO(3)) films are demonstrated to have equal performance to hole-injection layers composed of either PEDOT:PSS or thermally evaporated MoO(3) (eMoO(3)), and the annealing temperature at which the sol-gel layer begins to work is consistent with the thermodynamic analysis of the process. Finally, the shelf lifetime of devices made with the sMoO(3) is similar to equivalent devices prepared with a eMoO(3) hole-injection layer.     

Upgraded antisolvent engineering enables 2D@3D quasi core-shell perovskite for achieving stable and 21.6％ efficiency solar cells

Perovskite solar cells(PSCs)have become a promising alternative to sustainable energy due to their high power conversion efficiency(PCE)and low-cost processing....     

Colloidal CuZnSnSe4−xSx nanocrystals for hybrid solar cells

We report the synthesis of different colloidal CZTSe_4−xS_x nanocrystals and their performance in [6,6]-phenyl C61 butyric acid methyl ester (PCBM) based organic/inorganic hybrid bulk heterojunction solar cells. Synthesis of colloidal CuZnSnSe_4−xS_x were performed and characterized by XRD, TEM, SEM, UV–Visible absorption techniques. Electrochemical and photovoltaic properties were investigated. The best device concept, ITO/PEDOT:PSS/CZTS:PCBM blend (1:10)/Al, showed 280 μA/cm² short circuit current, I_sc with 300 mV open circuit voltage V_oc, and fill factor FF of 0.38.     

High-performance planar heterojunction perovskite solar cells： Preserving long charge carrier diffusion lengths and interracial engineering

We demonstrate that charge carrier diffusion lengths of two classes of perovskites, CH3NH3PbI3-xClx and CH3NH3PbI3, are both highly sensitive to film processing conditions and optimal processing procedures are critical to preserving the long carrier diffusion lengths of the perovskite films. This understanding, together with the improved cathode interface using bilayer-structured electron transporting interlayers of [6,6]-phenyl-C61-butyric acid methyl ester （PCBM）/ZnO, leads to the successful fabrication of highly efficient, stable and reproducible planar heterojunction CH3NH3PbI3-xCl2 solar cells with impressive power-conversion efficiencies （PCEs） up to 15.9%. A 1-square-centimeter device yielding a PCE of 12.3% has been realized, demonstrating that this simple planar structure is promising for large-area devices.     

Influence of SCN− moiety on CH3NH3PbI3 perovskite film properties and the performance of carbon-based hole-transport-layer-free perovskite solar cells

Journal of Materials Science: Materials in Electronics - CH3NH3PbI3 perovskite films were prepared via a hot-casting method using six different CH3NH3I, PbI2 and Pb(SCN)2 solutions. Surface...     

Semiconductor based photoelectrochemical cells for solar energy conversion—An overview

An overview of the semiconductor based photoelectrochemical (pec) cells for solar energy conversion is presented.pec cells are of two types: photoelectrolysis cells and photovoltaic cells. The principles involved, electrode and electrode/electrolyte interface characteristics, experimental methods of investigation and energy conversion efficiency are discussed in detail. Up-to-date data on variouspec cells are also presented and discussed.     

HFCVD grown graphene like carbon–nickel nanocomposite thin film as effective counter electrode for dye sensitized solar cells

The two step processes of hot filament chemical vapor deposition (HFCVD) and DC sputtering were used to grow graphene like carbon (GLC)–nickel (Ni) nanocomposite thin film on fluorine-doped tin oxide (FTO) glass and applied as counter electrode (CE) for dye sensitized solar cells (DSSCs). The morphological and absorption properties revealed uniform GLC–Ni thin film with reasonable transmittance. The GLC–Ni thin film showed enhanced electrical conductivity as compared to FTO. The good electrocatalytic activity towards iodide ions in redox electrolyte was showed by the prepared GLC–Ni/FTO thin film electrode. The fabricated DSSC with GLC–Ni/FTO counter electrode (CE) presented relatively moderate solar-to-electrical conversion efficiency of ∼3.1% with high short-circuit current density (J_SC) of ∼10.03 mA/cm², open circuit voltage (V_OC) of ∼0.663 V with fill factor (FF) of ∼0.45, which might attribute to enhanced electrical conductivity and the electrocatalytic activity of GLC–Ni/FTO CE.     

Equiaxed–columnar stacked TCO films for efficient silicon heterojunction solar cells

Journal of Materials Science: Materials in Electronics - Zr, Ti and Ga-doped indium oxide (ITGZO) films with different structures were prepared by radio frequency (RF) magnetron sputtering method....     

Low-temperature UV processing of nanoporous SnO₂ layers for dye-sensitized solar cells

Connection of SnO? particles by simple UV irradiation in air yielded cassiterite SnO? porous films at low temperature. XPS, FTIR, and TGA-MS data revealed that the UV treatment has actually removed most of the organics present in the precursor SnO? colloid and gave more hydroxylated materials than calcination at high temperature. As electrodes for dye-sensitized solar cells (DSCs), the N3-modified 1-5 μm thick SnO? films showed excellent photovoltaic responses with overall power conversion efficiency reaching 2.27% under AM1.5G illumination (100 mW cm?2). These performances outperformed those of similar layers calcined at 450 °C mostly due to higher V(oc) and FF. These findings were rationalized in terms of slower recombination rates for the UV-processed films on the basis of dark current analysis, photovoltage decay, and electrical impedance spectroscopy studies.     

Mechanical synthesis of high purity Cu–In–Se alloy nanopowder as precursor for printed CISe thin film solar cells

Mechanical alloying and ball milling are low cost, up-scalable techniques for the preparation of high purity chalcogenide nanopowders to be used as precursor material for printing thin film solar cells. In this study, high purity copper indium selenium (Cu–In–Se) alloy nanopowders with 20–200 nm particle size were synthesized from macroscopic elemental Cu, In and Se powders via mechanical alloying and planetary ball milling. The particle size distribution, morphology, composition, and purity level of the synthesized Cu–In–Se alloy nanopowders were investigated. Thin Cu–In–Se alloy nanopowder ink coatings, deposited on Mo-coated glass substrates by doctor blading, were converted into a CuInSe₂ semiconductor film by selenization heat treatment in Se vapor. The CuInSe₂ film showed semiconducting band gap around 1 eV measured by photoluminescence spectroscopy. CuInSe₂ absorber layer based thin film solar cell devices were fabricated to assess their performance. The solar cell device showed a total efficiency of 4.8%, as measured on 0.25 cm² area cell.     

Simple indoline based donor–acceptor dye for high efficiency dye-sensitized solar cells

A simple metal-free donor–acceptor type sensitizer U01, bearing strong electron donor indoline-triphenylamine was synthesized for panchromatic sensitization of TiO₂ nanocrystalline film. Photovoltaic properties of U01 showed remarkably enhanced light harvesting due to the presence of strong electron donor and robust structure. The new U01 sensitized solar cell exhibited a photovoltaic performance: a short-circuit photocurrent density (J_sc) of 10.70 mA cm⁻², an open-circuit photovoltage (V_oc) of 0.758 V and a fill factor (FF) of 0.74, corresponding to an overall conversion efficiency of 6.01% under standard global AM 1.5 solar light condition. Our results suggest that indoline-triphenylamine based robust D–A molecular architecture is a highly promising class of panchromatic sensitizers for improvement of the performance of dye-sensitized solar cells (DSCs).     

Defect passivation strategy for inorganic CsPbI2Br perovskite solar cell with a high-efficiency of 16.77％

All-inorganic halide perovskite solar cells(PSCs)have acquired great progress,especially CsPbI2Br.However,their photoelectric conversion efficiency(PCE)remains far below the theoretical predictions.Non-radiative recombination is one of the important issues affecting the photoelectric performance of the PSCs,and the defective lead ions derived from the evaporation of halide ions in the inorganic per-ovskite are the principal non-radiative recombination centers.Herein,the non-radiative recombination is effectively suppressed by introducing the N-methyl-2-pyrrolidone(NMP)as a Lewis base molecule to passivate the defective lead ions.Therefore,by adjusting the dosage of NMP,the smooth and pinhole-free CsPbI2Br perovskite film is obtained and the optimized device exhibits a champion PCE of 16.77％with an excellent fill factor(FF)of 0.80.This work proves the effectiveness of passivation using Lewis base molecules to prevent non-radiative recombination defects in inorganic perovskite.     

TiO₂ photoanode structure with gradations in V concentration for dye-sensitized solar cells

V-TiO?(GC) photoanode film with graduated structure was prepared in a dye-sensitized solar cell work electrode by layer-by-layer method using TiO? precursor with gradations in V concentration on the indium tin oxide transparent conducting glass from substrate to surface. The effects of the gradient in V concentration on the structures and properties of TiO? photoanode film were discussed. The structure of the gradient V concentration has remarkable influence on the final performance of the DSSCs and I-V characteristic measurement indicates an enhanced efficiency by 31% as compared to pure TiO? nanoparticles film samples due to abundant solar light, fast injection and transmission velocity and the slowdown recombination of photoexcited electrons, simultaneously.     

Sodium fluoride-assisted modulation of anodized TiO₂ nanotube for dye-sensitized solar cells application

This work reports the use of sodium fluoride (in ethylene glycol electrolyte) as the replacement of hydrofluoric acid and ammonium fluoride to fabricate long and perpendicularly well-aligned TiO? nanotube (TNT) (up to 21 μm) using anodization. Anodizing duration, applied voltage and electrolyte composition influenced the geometry and surface morphologies of TNT. The growth mechanism of TNT is interpreted by analyzing the current transient profile and the total charge density generated during anodization. The system with low water content (2 wt %) yielded a membrane-like mesoporous TiO? film, whereas high anodizing voltage (70 V) resulted in the unstable film of TNT arrays. An optimized condition using 5 wt % water content and 60 V of anodizing voltage gave a stable array of nanotube with controllable length and pore diameter. Upon photoexcitation, TNTs synthesized under this condition exhibited a slower charge recombination rate as nanotube length increased. When made into cis-diisothiocyanato-bis(2,2?-bipyridyl-4,4?-dicarboxylato) ruthenium(II) bis (tetrabutyl-ammonium)(N719) dye-sensitized solar cells, good device efficiency at 3.33 % based on the optimized TNT arrays was achieved with longer electron time compared with most mesoporous TiO? films.     

Optimization of sensitized perovskite solar cells with Zn–Cu–In–Se quantum dots to increase quantum efficiency

Journal of Materials Science: Materials in Electronics - Perovskite solar cells are efficient units in systems with modern renewable energy sources. Increasing the efficiency of solar cells is...     

Simple preparation of highly efficient MAxFA1−xPbI3 perovskite films from an aqueous halide-free lead precursor by all dip-coating approach and application in high-performance perovskite solar cells

Journal of Materials Science - All sequential-dip-coating deposition of mixed organic cationic MAxFA1?xPbI3 perovskite films from an aqueous non-halide lead precursor solution was effectively...     

An organic D-π-A dye for record efficiency solid-state sensitized heterojunction solar cells

The high molar absorption coefficient organic D-π-A dye C220 exhibits more than 6% certified electric power conversion efficiency at AM 1.5G solar irradiation (100 mW cm(-2)) in a solid-state dye-sensitized solar cell using 2,2',7,7'-tetrakis(N,N-dimethoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD) as the organic hole-transporting material. This contributes to a new record (6.08% by NREL) for this type of sensitized heterojunction photovoltaic device. Efficient charge generation is proved by incident photon-to-current conversion efficiency spectra. Transient photovoltage and photocurrent decay measurements showed that the enhanced performance achieved with C220 partially stems from the high charge collection efficiency over a wide potential range.     

Synthesis and characterization of novel D–A porphyrin-containing copolymers for polymer solar cells

A novel asymmetrical D–A zinc porphyrin derivative with dimehtyl triphenylamine (donor unit) and methyl benzoate (acceptor unit) as para-arms was first synthesized. Then, two new copolymers (P1 and P2) containing D–A zinc porphyrin derivatives were synthesized by the Stille coupling method and applied in PSCs. Their structures, photophysical and electrochemical properties were characterized by ¹H NMR, ¹³C NMR, gel permeation chromatography, thermogravimetric analysis, UV–vis absorption spectroscopy, photoluminescence spectroscopy, and cyclic voltammetry. The two copolymers exhibited good thermal stability and film-forming ability. The results showed that P1 containing D–A zinc porphyrin exhibits a strong absorption in the range of 400–500 nm. By the introduction of thiophene derivative with 4,7-di(4-hexylthiophen-2-yl)benzothiadiazole (T-DTBT) conjugated side-chain unit, P2 showed broader absorption in the region of 300–650 nm than P1. The photoluminescence spectra made clear that charge transfer between the whole main chain and side chain can be effective. Cyclic voltammograms revealed that the LUMO energy levels of P2 was reduced in comparison with P1 due to the introduction of electron-deficient T-DTBT conjugated side-chain unit, indicating that electron-injection and transporting properties have been improved. Polymer solar cells were fabricated based on the blend of the copolymers and methanofullerene[6,6]-phenyl C₆₁-butyric acid methyl ester (PC₆₁BM). The PSC based on P2:PC₆₁BM (1:2, w/w) exhibited a power conversion efficiency of 1.26% under AM 1.5, 100 mW cm⁻².