Unveiling the origin of performance enhancement of photovoltaic devices by upconversion nanoparticles

To better utilize the infrared(IR)region in sunlight for photovoltaic devices(PVs),upconversion nanoparticles(UCNPs)have been proposed to improve power conversion efficiency(PCE).However,researchers recently have found that the upconversion(UC)effect is negligible in PVs performance improvement for their ultra-low UC photoluminescence quantum yields of UCNPs solid film,while the real mechanism of UCNPs in PVs has not been clearly studied.Herein,based on the material inorganic perovskitesγ-CsPbI₃,NaYF₄:20%Yb³⁺,2%Er³⁺UCNPs were integrated into different transport layer to optimize device performance.Compared with reference device,the short-circuit current density and PCE of optimized device reached 20.87 mA/cm²(20.39 mA/cm²)and 18.34%(17.72%),respectively,without sacrificing open-circuit voltage and filling factor.Further experimental characterizations verified that the improved performance was attributable to enhanced visible light absorption instead of IR.To theoretically explain the statement,the light field distribution in device was simulated and the absorption in different layers was calculated.The results revealed that the introduction of UCNPs with different refractive index from other layers caused light field disturbance,and improved visible light captured by γ-CsPbI₃.Importantly,through experiments and theoretical calculation,the research deeply explored the potential mechanism of UCNPs in optimizing PVs performance.     

Photo-driven water splitting photoelectrochemical cells by tandem organic dye sensitized solar cells with I−/I3− as redox mediator

Dye-sensitized photoelectrochemical tandem cells have shown the promise for light driven hydrogen production from water owing to the low cost,wide absorption spectra in the visible region and ease to process of their constitutive photoelectrode materials.However,most photo-driven water splitting photoelectrochemical cells driven by organic dye sensitized solar cells exhibit unsatisfactory hydrogen evolution rate,primarily attributed to their poor light capturing ability and low photocurrent performance.Here we present the construction of a tandem system consisting of an organic blue-colored S5 sensitizer-based dyesensitized photoelectrochemical cell(DSPEC) wired in series with three spectral-complemental dyes BTA-2,APP-3 and APP-1 sensitizers-based dye-sensitized solar cell(DSC),respectively.The two spectral-complemental chromophores were used in DSC and DSPEC to ensure that the full solar spectrum could be absorbed as much as possible.The results showed that the photocurrent of tandem device was closely related to the open-circuit voltage(Voc) of sensitized DSC,in which the tandem configuration consisting of S5 based DSPEC and BTA-2 based DSC gave the best photocurrent.On this basis,tandem device with the only light energy and no external applied electrical bias was further constructed of BTA-2 based 2-junction DSC and S5 based DSPEC and obtained a photocurrent of 500 μA cm-2 for hydrogen generation.Furthermore,I-/I3-was used as a redox couple between dye regeneration and O2 production on the surface of Pt-IrO2/WO3.The strategy opens up the application of pure organic dyes in DSC/DSPEC tandem device.     

Synthesis and photovoltaic properties of new europium complex Eu（DBM）3（CPyBM）

A new europium（Ⅲ） complex, tris（dibertzoylmethanate）{ 1-[9-hexyl-9-carbazole]-2-（2-pyridyl）-bertzimidazole}europium（Ⅲ） [Eu（DBM）a（CPyBM）] was synthesized and used as an electron-acceptor and electron-transport layer in organic photovoltaic （PV） device. Power conversion efficiency achieved from the device was 1.04% under illumination with 365 nm UV light at 1.6 mW/cm^2. Compared with the previous reported devices based on Eu（Ⅲ） complexes, the PV performances were improved. The working mechanism of the organic PV device was discussed.     

Photophysical and Photoelectric Properties of 2—{[4—（N—Hexadecyl—N—methylamino）phenyl]methylene}—propanedinitrile

2-{[4-(N-Hexadecyl-N-methylamino)phenyl]methylene}-propanedinitrile(HMAPN) with typical donor-π-acceptor(D-π-A）structure was synthesized.It could be easily assembled into stable films by LB technique.The photophysical properties of HMAPN were investigated in solution and on LB films.The photoelectric properties of HMAPN were examined and the anodic photocurrent of the ITO electrode modified by the monolayer LB film of HMAPN was measured as 835 nA/cm^2 under the white light of 218.2 mW/cm^2 without bias voltage.The effects of light intensity,bias voltage on the photocurrent were discussed.The possible mechanism of the photocurrent formation was given.     

Photoinduced energy transfer and charge transfer on squarylium cyanine dyes

A series of squarylium cyanine dyes (Sqs) were synthesized to explore their applications in functional devices.Preliminary investigation on the mechanism involved in these devices was carried out.Spectroscopic behavior of Sqs with porphyrin (P),8-hydroxyquinolium aluminum (Alq) and ruthenium bipyridyl complex (Ru(bipy)) in solution,in film and on nanocrystalline TiO2 was investigated,respectively.A mechanism including photoinduced energy transfer and charge transfer processes was suggested in the corresponding practical devices.By means of doping,a red organic electroluminescent device (ELD) using Sq-doped Alq as the emission layer (EML) has been developed,and the total light to electricity efficiency of nanocrystalline TiO2 electrode based on using Sq-doped Ru(bipy) as photosensitizer has been improved greatly in the whole visible region,particularly in the red area above 600 nm.     

Efficient Hybrid Photovoltaic Devices Based on in-situ Electrochemical Copolymerization of 3-Methylthiophene and Bithiophene into Pores of Nanocrystalline TiO2

Novel organic and inorganic hybrid photovoltaic devices were thbricated by in-situ electrochemical copolymerization of 3-methylthiophene（3MT） and bithiophene（BT） into the pores of nanostructured TiO2 sintered on fluorine-doped tin oxide（FTO） substrate. The photoactive layer was investigated by Fourier transform infrared（FTIR） spectroscopy, ultraviolet-visable（UV-Vis） spectrometer, scanning electron microscope（SEM） and cyclic voltammo- gram characterization. Device efficiency based on different molar feed ratios of 3MT and BT during electrochemical polymerization, and the effect of in-situ copolymer state（doped by electrolyte and de-doped） were measured and compared. Under the solar illumination of 100 mW/cm2（AM 1.5）, an optimized device efficiency of 0.938% was obtained when the molar ratio of 3MT to BT was 500：1, polymerization time was 500 s and the system was in doped copolymer state, respectively. The mechanism of overall photovoltaic parameter improvement was discussed.     

Mixed-phase Mesoporous TiO2 Film for High Efficiency Perovskite Solar Cells

Mesoporous scaffold structures have played great roles in halide perovskite solar cells(PSCs),due to the excellent photovoltaic performance and commercial perspective of mesoporous PSCs.Here,we reported a mixed-phase TiO2 mesoporous film as an efficient electron transport layer(ETL)for mesoporous perovskite solar cells.Due to the improved crystal phase,fihn thickness and nanopartMe size of TiO2 layer,which were controlled by varying the one-step hydrothermal reaction time and annealing time,the PSCs exhibited an outstanding short circuit photocurrent density of 25.27 mA/cm^2,and a maximum power conversion efficiency(PCE)of 19.87%.It is found that the ultra-high Jsc attributes to the excellent film quality,light capturing and excellent electron transport ability of mixed-phase TiO2 mesoporous film.The results indicate that mix-phase mesoporous metal oxide fihns could be a promising candidate for producing effective ETLs and high efficiency PSCs.     

Photoelectrochemical properties of MWCNT-TiO2 hybrid materials as a counter electrode for dye-sensitized solar cells

The MWCNT-Ti02 hybrid materials were prepared by a simply mixing method and used as a counter electrode （CE） for dye-sensitized solar cells. Compared with the platinum CE, MWCNT-TiO2 CE has the similar redox voltage and current response in the cyclic voltammetry. The electrochemical catalytic activity was characterized by the electrochemical impedance spectroscopy and Tafel curve, including the equivalent circuit, the exchange current density, the limiting diffusion current density, and the diffusion coefficient of triiodide/iodide redox species. The results indicate that the reduction process from triiodide to iodide is determined by the kinetic-controlled and diffusion-limited processes. The device performance is optimal based on the MWCNT-TiO2 （mass ratio of 2：1） CE, such as the open-circuit voltage of 0.72 V, the short-circuit photocurrent density of 15.71 mA/cm2, the fill factor of 0.68, and the photon-to-electron conversion efficiency of 7.69%.     

Hybrid solar cells constructed of macroporous n-type GaP coated with PEDOT:PSS

Hybrid organic–inorganic solar cell devices were fabricated utilizing macroporous n-type Ga P and poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate)(PEDOT:PSS).The high-aspect ratio structures of the macroporous Ga P resulted in higher photocurrent and external quantum yield as a function of wavelength.Photocurrent–voltage measurements as a function of light intensity revealed information on the dependence of short-circuit current(Jsc) and open-circuit voltage(Voc) on light intensity.Under 1.0 Sun illumination,hybrid macroporous Ga P/PEDOT:PSS devices showed Jscof2.34 m A cmà2,Vocof 0.95 V,fill factor of 0.54,and overall efficiency of 1.21%.The extent of the influence of dopant density of Ga P on hybrid device performance was probed with current density–voltage measurements.The addition of a gold nanoparticle coating on macroporous Ga P prior to PEDOT:PSS coating showed increased device performance,with overall efficiency of 1.81%.Gold-modified planar Ga P/PEDOT:PSS showed decreased Jscand Vocvalues and lower external quantum yield over all wavelengths.     

Two Photoelectrochemical Processes for TiO2 Electrode under UV Illumination

TiO2 thin film electrode was prepared by a sol-gel method on ITO substrates. Cyclic voltammetric behavior of the ITO/TiO2 electrode under ultraviolet (UV) illumination was investigated in the solution of Na2SO4.There are two photoelectrochemical processes for TiO2 electrode under UV illumination.One is a fast process,which results in the appearance of anodic photocurrent.The anodic photocurrent will appear and disappear with the light on and off.The other is a slow process,which will be responsible for the appearance of an oxidative peak. When the electrode is illuminated under UV light for a long time,a new oxidative peak can be observed.The peak current increases with the increase of UV illumination time.It is assumed that the new peak belongs to the oxidation of Ti^3 ,which formed and accumulated on the electrode surface during the UV illumination.A detailed mechanism is proposed on the base of these two photoelectrochemical processes.It is assumed that the change of hydrophilicity of TiO2 thin film may be related to the slow process while the film irradiated by UV light.     

High open-circuit voltage in UV photovoltaic cell based on polymer/inorganic bilayer structure

Polymer/inorganic hybrid ultra violet (UV) photovoltaic device is fabricated by using poly(N-vinyl-carbazole) (PVK) and zinc sulfide (ZnS). The device shows promising photovoltaic characteristics with a high open-circuit voltage of 1.65 V, and a short-circuit current of 46.8 μA/cm² under the illumination of 340 nm UV light with the intensity of 14 mW/cm². Besides, much correlative photocurrent spectra of the device under forward and reverse applied bias manifest the transport mechanism of charge carriers in PVK/ZnS bilayer systems.     

Sea urchin TiO2-nanoparticle hybrid composite photoelectrodes for CdS/CdSe/ZnS quantum-dot-sensitized solar cells

The sea urchin TiO(2) (SU TiO(2)) particles composed of radially aligned rutile TiO(2) nanowires are successfully synthesized through the simple solvothermal process. SU TiO(2) was incorporated into the TiO(2) nanoparticle (NP) network to construct the SU-NP composite film, and applied to the CdS/CdSe/ZnS quantum-dot-sensitized solar cells (QDSSCs). A conversion efficiency of 4.2% was achieved with a short-circuit photocurrent density of 18.2 mA cm(-2) and an open-circuit voltage of 531 mV, which corresponds to ～20% improvement as compared with the values obtained from the reference cell made of the NP film. We attribute this extraordinary result to the light scattering effect and efficient charge collection.     

Quantum-dot-sensitized solar cells fabricated by the combined process of the direct attachment of colloidal CdSe quantum dots having a ZnS glue layer and spray pyrolysis deposition

We were able to attach CdSe quantum dots (QDs) having a ZnS inorganic glue layer directly to a mesoporous TiO(2) (mp-TiO(2)) surface by spray coating and thermal annealing. Quantum-dot-sensitized solar cells based on CdSe QDs having ZnS as the inorganic glue layer could easily transport generated charge carriers because of the intimate bonding between CdSe and mp-TiO(2). The application of spray pyrolysis deposition (SPD) to obtain additional CdSe layers improved the performance characteristics to V(oc) = 0.45 V, J(sc) = 10.7 mA/cm(2), fill factor = 35.8%, and power conversion efficiency = 1.7%. Furthermore, ZnS post-treatment improved the device performance to V(oc) = 0.57 V, J(sc) = 11.2 mA/cm(2), fill factor = 35.4%, and power conversion efficiency = 2.2%.     

Enhanced light harvesting in mesoporous TiO2/P3HT hybrid solar cells using a porphyrin dye

We report panchromatic light harvesting in hybrid TiO(2)/P3HT photovoltaic devices using a porphyrin dye that complements the light absorption of P3HT. The high short circuit photocurrent (12.1 mA cm(-2)) obtained is found to be due, in part, to F?rster resonance energy transfer from the P3HT to the dye.     

Enhancing visible light photo-oxidation of water with TiO2 nanowire arrays via cotreatment with H2 and NH3: synergistic effects between Ti3+ and N

We report a synergistic effect involving hydrogenation and nitridation cotreatment of TiO(2) nanowire (NW) arrays that improves the water photo-oxidation performance under visible light illumination. The visible light (>420 nm) photocurrent of the cotreated TiO(2) is 0.16 mA/cm(2) and accounts for 41% of the total photocurrent under simulated AM 1.5 G illumination. Electron paramagnetic resonance (EPR) spectroscopy reveals that the concentration of Ti(3+) species in the bulk of the TiO(2) following hydrogenation and nitridation cotreatment is significantly higher than that of the sample treated solely with ammonia. It is believed that the interaction between the N-dopant and Ti(3+) is the key to the extension of the active spectrum and the superior visible light water photo-oxidation activity of the hydrogenation and nitridation cotreated TiO(2) NW arrays.     

Near-IR light-sensitized voltaic conversion system using nanocrystalline TiO2 film by Zn chlorophyll derivative aggregate

A Zn chlorophyll-a derivative, Zn chlorin-e6 (ZnChl-e6), adsorbed onto a nanocrystalline TiO2 film (ZnChl-e6/TiO2) electrode was prepared, and the photovoltaic properties of the ZnChl-e6/TiO2 electrode were studied. The absorption peaks of ZnChl-e6/TiO2 observed at 420, 654, and 795 nm were attributed to the ZnChl-e6 molecules aggregating onto TiO2 film. The fluorescence attributed to the ZnChl-e6 monomer and aggregate was observed at 710 and 820 nm, respectively, and the fluorescence in both cases was quenched by TiO2 particles. The maximum of the incident photon-to-current conversion efficiency (IPCE) value in the photocurrent action spectrum was 800 nm, and the IPCE value was 7.0%. ZnChl-e6 molecules formed aggregates on a nanocrystalline TiO2 film electrode. From the photocurrent-photovoltage characteristics of the ZnChl-e6/TiO2 electrode irradiated with 100 mW cm(-2), the short-circuit photocurrent (I(SC)) was found to be 0.19 mA cm(-2) and the open-circuit photovoltage (V(OC)) was found to be 375 mV. The maximum power was estimated to be 28.7 microW cm(-2), and the fill factor (FF) was estimated to be 40.1%. A near-IR light induced photovoltaic conversion system using a ZnChl-e6 aggregate formed onto a nanocrystalline TiO2 film electrode was achieved.     

PbS/CdS-sensitized mesoscopic SnO2 solar cells for enhanced infrared light harnessing

Metal oxide semiconductors with lower lying conduction band minimum and superior electron mobility are essential for efficient charge separation and collection in PbS-sensitized solar cells. In the present study, mesoscopic SnO(2) was investigated as an alternative photoanode to the commonly used TiO(2) and examined comprehensively in PbS-sensitized liquid junction solar cells. To exploit the capability of PbS in an optimized structure, cascaded nPbS/nCdS and alternate n(PbS/CdS) layers deposited by a successive ionic layer adsorption and reaction method were systematically scrutinized. It was observed that the surface of SnO(2) has greater affinity to the growth of PbS compared with TiO(2), giving rise to much enhanced light absorption. In addition, the deposition of a CdS buffer layer and a ZnS passivation layer before and after a PbS layer was found to be beneficial for efficient charge separation. Under optimized conditions, cascaded PbS/CdS-sensitized SnO(2) exhibited an unprecedented photocurrent density of 17.38 mA cm(-2) with pronounced infrared light harvesting extending beyond 1100 nm, and a power conversion efficiency of 2.23% under AM 1.5, 1 sun illumination. In comparison, TiO(2) cells fabricated under similar conditions showed much inferior performance owing to the less efficient light harnessing of long wavelength photons. We anticipate that the systematic study of PbS-sensitized solar cells utilizing different metal oxide semiconductors as electron transporters would provide useful insights and promote the development of semiconductor-sensitized mesoscopic solar cells employing panchromatic sensitizers.     

TiO_2-CuPcTs敏化薄膜光电流及可见光光催化性能

以四磺酸酞菁铜(CuPcTs)为敏化剂,玻璃和图案化的氧化铟锡(ITO)分别作为基底,制备了敏化薄膜TiO2-CuPcTs和ITO/TiO2-CuPcTs/ITO敏化器件.以罗丹明B(RhB)的可见光光催化降解为模型反应评价敏化薄膜的光催化性能.敏化薄膜采用UV-vis和Raman技术进行表征,同时利用敏化器件的结构特性,测定其在氮气和纯水体系下的光电流.研究结果表明,TiO2-CuPcTs可以有效地将光谱响应拓宽到可见光区,一级反应速率常数为空白TiO2薄膜的3.7倍.TiO2-CuPcTs薄膜光催化降解RhB的重复性能稳定.与ITO/TiO2/ITO器件相比,敏化器件ITO/TiO2-CuPcTs/ITO具有较高的光电流信号,验证了激发态的CuPcTs能够将电子转移到TiO导带上的敏化机理.     

Uncovering the role of the ZnS treatment in the performance of quantum dot sensitized solar cells

Among the third-generation photovoltaic devices, much attention is being paid to the so-called Quantum Dot sensitized Solar Cells (QDSCs). The currently poor performance of QDSCs seems to be efficiently patched by the ZnS treatment, increasing the output parameters of the devices, albeit its function remains rather unclear. Here new insights into the role of the ZnS layer on the QDSC performance are provided, revealing simultaneously the most active recombination pathways. Optical and AFM characterization confirms that the ZnS deposit covers, at least partially, both the TiO(2) nanoparticles and the QDs (CdSe). Photoanodes submitted to the ZnS treatment before and/or after the introduction of colloidal CdSe QDs were studied by electrochemical impedance spectroscopy, cyclic voltammetry and photocurrent experiments. The corresponding results prove that the passivation of the CdSe QDs rather than the blockage of the TiO(2) surface is the main factor leading to the efficiency improvement. In addition, a study of the ultrafast carrier dynamics by means of the Lens-Free Heterodyne Detection Transient Grating technique indicates that the ZnS shell also increases the rate of electron transfer. The dual role of the ZnS layer should be kept in mind in the quest for new modifiers for enhancing the performance of QDSCs.     

全固态平面型ITO/Fe^3＋-TiO2/ITO光电催化器件的制备和催化性能

在具有条形电极的ITO(氧化铟锡)玻璃上负载Fe3 -TiO2薄膜,得到全固态平面型ITO/Fe3 -TiO2/ITO光电催化器件.利用Keithley 2400数字源电流表对器件施以一定的偏压,以气相甲醛的降解为模型反应,对器件分别进行了空气和氮气条件下的光电催化性能测试.结果表明,甲醛的存在能够增强体系的光电流,并且在氮气下器件的光电流明显大于在空气下的光电流,说明甲醛参与了电子的迁移过程.ITO/Fe3 -TiO2/ITO器件表现出比ITO/Fe3 -TiO2/ITO器件更高的光催化活性,且前者的光电流值小于后者,说明掺杂Fe3 所引起的电子迁移率的降低远大于所引起的激子分离几率的提高.ITO/Fe3 -TiO2/ITO器件在外加偏压下活性提高,但提高的幅度没有ITO/TiO2/ITO器件明显.