Short-circuit Photocurrent Research Articles

Enhancing Perovskite Solar Cell Performance by Interface Engineering Using CH3NH3PbBr0.9I2.1 Quantum Dots.

To improve the interfacial charge transfer that is crucial to the performance of perovskite solar cells, the interface engineering in a device should be rationally designed. Here we have developed an interface engineering method to tune the photovoltaic performance of planar-heterojunction perovskite solar cells by incorporating MAPbBr3-xIx (MA = CH3NH3) quantum dots (QDs) between the MAPbI3 perovskite film and the hole-transporting material (HTM) layer. By adjustment of the Br:I ratio, the as-synthesized MAPbBr3-xIx QDs show tunable fluorescence and band edge positions. When the valence band (VB) edge of MAPbBr3-xIx QDs is located below that of the MAPbI3 perovskite, the hole transfer from the MAPbI3 perovskite film to the HTM layer is hindered, and hence, the power conversion efficiency decreases. In contrast, when the VB edge of MAPbBr3-xIx QDs is located between the VB edge of the MAPbI3 perovskite film and the highest occupied molecular orbital of the HTM layer, the hole transfer from the MAPbI3 perovskite film to the HTM layer is well-facilitated, resulting in significant improvements in the fill factor, short-circuit photocurrent, and power conversion efficiency.

Effect of Aging on the Photoelectrical Properties of AlGaInP LEDs

We report on the nonmonotonous variation of photoelectrical properties of commercial AlGaInP LEDs during the aging process. The light-generated current and short-circuit photocurrent were found to drop by the factors of 2 and 1.5, respectively, after about 3 h of aging at the rated forward current of 1400 mA with subsequent recovery and stabilization within $\sim 1000$ h of aging. The temporal minima of photocurrents were accompanied by increased photoconductivity revealed from the negative differential photovoltage under modulated photoexcitation as well as by the minimum of optical output and the maximum of the ideality factor of the LEDs at low forward currents. The observed temporal variation of the photoelectrical properties was attributed to the interplay of recombination-enhanced growth and annealing of defects responsible for nonradiative recombination and photoconductivity in the active and cladding layers of the LEDs, respectively.

Optical Microconcentrator System for Enhancing Solar Cell Photovoltaic Performances

In this paper, we present two optical microconcentrator systems consisting of an array of microlenses formed with an intermediate layer deposited between a textured glass plate and the front surface of a silicon solar cell and polydimethylsiloxane (PDMS) microlenses based on replication of molds etched on glass. The optical coupling microlenses are fabricated using simple photolithography techniques that make the design compatible with silicon technology and large-scale manufacturing.We experimented with a honeycomb texturization on Corning glass plate having an area of 2x2 cm2. A wet etching process that led to a transparent surface with micro-cavities of 20 μm diameter and a depth of 6 μm was used. The intermediate layer was chosen depending on the refractive index. Materials with the refractive index in the range of 1 - 1.43 were experimented. The structures of silicon solar cells covered with the intermediate layer and texturized glass were characterized by illuminating and measuring the short-circuit photocurrent. It was obtained an improvement of 6.7 % of the short-circuit photocurrent for the optical microconcentrator system solar cells as compared to a structure covered with an untextured glass plate without intermediate layer. The microconcentrator consisting of the PDMS microlenses gave better results, an increase of the photocurrent of over 9%.The simulations of this system were done by using an OptiFTDT software. The aim of the simulations was to establish the distribution of the radiation which crosses the optical microconcentrator system and hits the solar cells surface. The simulation results are in agreement with the obtained experimental data.

Enhanced photocurrent generation in bacteriorhodopsin based bio-sensitized solar cells using gel electrolyte

High purity light sensitive photoactive protein Bacteriorhodopsin (BR) was isolated successfully via a simple two phase extraction technique (ATPS) as an alternate method for the tedious sucrose gradient ultracentrifugation procedure (SGU). Bio sensitized solar cells (BSSCs) were fabricated by the integration of BR into TiO2 (photo anode) with acetamide based gel electrolytes and platinum (photo cathode) as a counter electrode. The structural and photoelectrical behaviours of BR and BSSCs were analyzed by Atomic Force Microscopy, Raman spectroscopy, photocurrent and photovoltage (IV) measurement and electrochemical impedance spectroscopy. The short circuit photocurrent (Jsc) and photoelectric conversion efficiency (η) of acetamide based gel electrolyte (AG) (1.08mAcm−2, 0.49%) are twice higher than that of traditional triiodide based liquid electrolyte (LE) (0.62mAcm−2, 0.19%). Also, quasi-Fermi level and lifetime of photogenerated electrons in acetamide based gel electrolyte is about four times higher than that observed in traditional triiodide redox electrolyte. A comparison of the observed results with similar BSSCs made of other natural photoactive protein systems shows that BR as sensitizer has better photovoltaic performance. The enhanced photocurrent generation of the BSSC constructed in our study could be due to the interaction of BR with acetamide based modified poly(ethylene)oxide (PEO) gel electrolyte.

Improvement in photovoltaic performance of perovskite solar cells by interface modification and co-sensitization with novel asymmetry 7-coumarinoxy-4-methyltetrasubstituted metallophthalocyanines

We report for the first time on both interface modification and co-sensitization by using novel asymmetry 7-coumarinoxy-4-methyltetrasubstituted metallophthalocyanines in a heterojunction solar cell. The short circuit photocurrent of mesoscopic heterojunction solar cell exhibits an improvement of more than 8%, while the PCEs give an increase of more than 28% compared to CH3NH3PbI3-sensitized devices, and the power conversion efficiencies reached at 13.96% most. The introduction of novel asymmetry metallophthalocyanines can not only favor crystal growth of CH3NH3PbI3 leading to a better carrier collection and retardation of charge recombination but also improve the light harvesting ability of perovskite resulting in a faster electron injection. Moreover, it can also reduce the hysteresis.

Quasi-solid-state dye-sensitized solar cell based on gel electrolyte with high gel to solution transition temperature using low molecular mass organogelator

Quasi-solid-state dye-sensitized solar cell (QS-DSSC) were fabricated using N,N'-1,4-butylenediylbis-dodecanamide as low molecular mass organogelator (LMOG). The gel to solution transition temperature (Tgel) of this gel electrolyte is 115.8 °C which ensures a good intrinsic stability of the gel electrolyte at the QS-DSSC operating temperature. The kinetic processes of electron transport and recombination of DSSCs influenced by the gel electrolyte are investigated in detail. Due to the diffusion of redox species in the gel electrolyte is hindered by the crosslinked network and the electron recombination at the interface of the TiO2 photoanode/electrolyte is accelerated, the incidental photon-to-electron conversion efficiency (IPCE) and the short circuit photocurrent density (Jsc) of the QS-DSSC are slightly decreased compared with those of liquid electrolyte based DSSC (L-DSSC). Remarkably, the QS-DSSC exhibits excellent thermal and light-soaking stabilities during accelerated aging tests for 1000 h. The QS-DSSC retains 90% of its initial photoelectric conversion efficiency, whereas that of L-DSSC only retains 83% under successive one sun light soaking with UV cut-off filter at 50 °C for 1000 h.

The effect of TiO2 photo anode film thickness on photovoltaic properties of dye-sensitized solar cells

Nanocrystalline titanium dioxide (TiO 2 ) photoanodes with four different film thicknesses from 5.57μm to 20.65μm were prepared by doctor-blade technique. Performance of dye sensitized solar cells (DSSCs) fabricated with these photoanodes were studied using current-voltage characteristics and incident photon-to-current conversion efficiency (IPCE) measurements. Electrochemical impedance spectroscopy (EIS) was used to analyze the effect of TiO 2 film thickness on the charge transfer resistance and electron life time in the solar cells. Voltage decay measurements were used to study the recombination process of photo generated charge carriers. These studies revealed that the photovoltaic properties of DSSCs largely depend on the film thickness of TiO 2 photoanode. Further, the DSSCs fabricated using a TiO 2 film of 12.73 μm thickness exhibited the best photovoltaic performance with highest incident photon-to-current conversion efficiency, highest short-circuit photocurrent, lowest charge transfer resistance, highest electron life time and lowest recombination life time.

Nitrogen-doped&SnO2-incoportaed TiO2 nanofibers as novel and effective photoanode for enhanced efficiency dye-sensitized solar cells

Although, titanium dioxide (TiO2) is the most widely used photoanode material in the dye-sensitized solar cells, the low tendency for dye adsorption, fast electrons/holes recombination and the poor electrons transfer are considered important reasons for the corresponding low photovoltaic efficiency. To overcome these problems, combining the versatility of the hydrothermal and electrospinning processes was exploited to synthesize novel nitrogen doped & tin oxide (SnO2) co-incorporated good morphology TiO2 nanofibers to be used as photoanode material. Experimentally, compared to pristine, nitrogen-doped and nitrogen-free&SnO2-incorporated TiO2 nanofibers, the novel electrode shows higher dye adsorption capacity and strong improvement in the charges recombination at the photoanode/electrolyte interface. Investigation of the photovoltaic efficiency indicated that SnO2 content should be optimized; the best result was obtained at 10wt%. Moreover, nitrogen doping enhances the cell efficiency based on both pristine and SnO2-incorporated TiO2 nanofibers. Typically, the estimated photovoltaic efficiencies for the fabricated cells based on pristine, nitrogen-doped, SnO2-incorportaed, and nitrogen-doped&SnO2-incorportaed TiO2 nanofibers were 1.61%, 4.41%, 3.41% and 5.01%, respectively. The enhancement of the photovoltaic efficiency for the introduced nanofibers can be attributed to two reasons. Firstly, compared to the other formulations, the introduced electrode shows the maximum short circuit photocurrent (Jsc); 8.74mA/cm2, which can be attributed to the enhancement of the dye adsorption, improving in the charge transfer, and decreasing of the electrons/holes recombination. Secondly, SnO2 incorporation leads to creates new routes for transferring the electrons from LUMO state of photosensitizer to the external circuit through the conduction band of this hetero structure and also wider the band gap which retards the recombination reactions.

Semiconductor Quantum Dot Sensitized Solar Cells Based on Ferricyanide/Ferrocyanide Redox Electrolyte Reaching an Open Circuit Photovoltage of 0.8 V.

Semiconductor quantum dot sensitized solar cells (QDSSCs) have rapidly been developed, and their efficiency has recently exceeded 9%. Their performances have mainly been achieved by focusing on improving short circuit photocurrent employing polysulfide electrolytes. However, the increase of open circuit photovoltage (VOC) cannot be expected with QDSSCs based on the polysulfide electrolytes owing to their relatively negative redox potential (around -0.65 V vs Ag/AgCl). Here, we demonstrate enhancement of the open circuit voltage by employing an alternative electrolyte, ferricyanide/ferrocyanide redox couple. The solar cell performance was optimized by investigating the influence of ferricyanide and ferrocyanide concentration on their interfacial charge transfer and transport kinetics. The optimized ferricyanide/ferrocyanide species concentrations (0.01/0.2 M) result in solar energy conversion efficiency of 2% with VOC of 0.8 V. Since the potential difference between the TiO2 conduction band edge at pH 7 and the electrolyte redox potential is about 0.79 V, although the conduction band edge shifts negatively under the negative bias application into the TiO2 electrode, the solar cell with the optimized electrolyte composition has nearly reached the theoretical maximum voltage. This study suggests a promising method to optimize an electrolyte composition for maximizing solar energy conversion efficiency.

Role of nanocone and nanohemisphere arrays in improving light trapping of thin film solar cells

A new crystalline silicon solar cell with Si nanocone arrays on the top and Al nanohemisphere arrays on bottom surface were proposed. The light-trapping ability were systematically studied by COMSOL Multiphysics. The nanocone arrays benefit light-trapping by introducing gradient change of refractive index and coupling the incoming light into optical modes. The metallic nanohemisphere arrays affect the light-harvesting by surface plasmon polaritons (SPPs) and scattering effect. The numerical simulations show that the optimal parameters for the periodic nanocone arrays are 350nm in diameter and 1.1 of the pitch/diameter ratio. The optimal parameters for the nanohemisphere arrays are 160nm in diameter, 1.3 of the pitch/diameter ratio respectively. Eliminating the Ohmic Loss in metallic nanohemisphere, a 700nm thick silicon solar cell with the combination of these two nanostructures will contribute an average absorption of 72.928% and a 33.311mA/cm2 short circuit photocurrent density in the wavelength of 310–1127nm.

P-Type dye-sensitized solar cells: Enhanced performance with a NiO compact blocking layer

A photoactive NiO electrode for p-type dye-sensitized solar cells (p-DSCs) has been equipped by the introduction of different coatings of a compact NiO blocking layer. This study examined the facile process for the fabrication of a compact NiO blocking layer by decomposing an ethanolic precursor solution of nickel acetate tetrahydrate. The P1-dye used as the photosensitizer for the NiO electrode in the p-DSCs device and their performances have been analyzed. The enhancement of both short-circuit photocurrent (Jsc) and fill factor (FF) resulted in a twofold increase in the power conversion efficiency (η). The electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) measurements demonstrated that charge recombination was suppressed when a compact NiO blocking layer was applied. The best p-DSC was achieved by employing spin-coated process for twice. The carrier lifetime of all the devices with a compact NiO blocking layer was improved compared to the bare cell.

Synthesis of new dithieno[3,2-b:2′,3′-d]pyrrole (DTP) dyes for dye-sensitized solar cells: effect of substituent on photovoltaic properties

A new series of triarylamine-free organic dyes based on dithieno[3,2-b:2′,3′-d]pyrrole has been synthesized for dye-sensitized solar cells (DSSCs). The photophysical properties and DSSC performances of these dyes have been characterized. The effects of substituent in dithieno[3,2-b:2′,3′-d]pyrrole on the performance of the dyes have been investigated by their absorption spectra, electrochemical and photovoltaic properties. In comparison with the hexyl, the incorporation of 4-hexyloxyphenyl in dithieno[3,2-b:2′,3′-d]pyrrole has resulted in an improved light harvesting capacity, stability and thus photocurrent as well as efficiency of cells. X69 sensitized DSSCs affords a short circuit photocurrent of 12.1 mA cm−2, an open circuit voltage of 520 mV, and a fill factor of 0.67, corresponding to an overall conversion efficiency of 4.21% under standard AM 1.5 sunlight.

Light trapping of crystalline Si solar cells by use of nanocrystalline Si layer plus pyramidal texture

The surface structure chemical transfer (SSCT) method has been applied to fabrication of single crystalline Si solar cells with 170μm thickness. The SSCT method, which simply involves immersion of Si wafers in H2O2 plus HF solutions and contact of Pt catalyst with Si taking only ∼30s for 6 in. wafers, can decrease the reflectivity to less than 3% by the formation of a nanocrystalline Si layer. However, the reflectivity of the nanocrystalline Si layer/flat Si surface/rear Ag electrode structure in the wavelength region longer than 1000nm is high because of insufficient absorption of incident light. The reflectivity in the long wavelength region is greatly decreased by the formation of the nanocrystalline Si layer on pyramidal textured Si surfaces due to an increase in the optical path length. Deposition of phosphosilicate glass (PSG) on the nanocrystalline Si layer for formation of pn-junction does not change the ultralow reflectivity because the surface region of the nanocrystalline Si layer possesses a refractive index of 1.4 which is nearly the same as that of PSG of 1.4–1.5. The PSG layer is found to passivate the nanocrystalline Si layer, which is evident from an increase in the minority carrier lifetime from 12 to 44μs. Hydrogen treatment at 450°C further increases the minority carrier lifetime approximately to a doubled value. The solar cells with the <front Ag electrode/nanocrystalline Si layer/pyramidal Si substrate/boron-diffused back surface field/Ag rear electrode> structure show a high conversion efficiency of 18.5% in spite of the simple cell structure without antireflection coating. In this case, the short circuit photocurrent density is 40.1mA/cm2 under AM1.5 100mW/cm2 irradiation.

Formation and properties of PZT-PbO thin heterophase films

ABSTRACTThe structural, electrophysical and photogalvanic properties of thin Pb(Ti0,47Zr0,53)O3+xPbO films obtained by the sol-gel process were investigated as a function of PbO concentration. Samples without lead excess showed dependence of the photocurrent direction from the preliminary direction of polarization in the absence of photoresponse in the unpolarized state. The PZT films with 5-15 mol. % lead excess are characterized by unipolar short-circuit photocurrent. Increasing the concentration of PbO in the solution up to 30 mol. % leads to extinction throughout the thickness of the columnar structure film crystallites and reduction of short-circuit photocurrent amplitude.

Schottky Barriers Based on Nanoporous InP with Gold Nanoparticles.

Schottky barrier structures based on nanoporous InP with inclusion of Au nanoparticles and evaporated semitransparent Au film have been made. The spectra of short-circuit photocurrent in the visible range and current-voltage characteristics have been measured. Prepared structures are characterized by increased photocurrent due to the microrelief interface and surface plasmon excitation in gold nanoparticles as well as increased surface recombination especially in the short wavelength region.

Dye-Sensitized Solar Cells in Humidity Environment: A Suitable Fabrication Procedure and Outdoor Test of Cell Stability

The performance of dye-sensitized solar cells (DSCs) fabricated by conventional procedure in humid environment have rapidly declined in outdoor testing. This fact may be caused due to the uptake of water into cells during the process of dye soaking (around 20 - 24 hours) and electrolyte filling under ambient air. In this work a new fabrication procedure, that proved to prevent the water uptake, was established for DSC assembling in high humidity environment. In the procedure, the sandwich cell, assembled from preparative FTO/TiO2 and FTO/Pt electrodes was filled with N719 (10 mM)/DMF solution for the dye adsorption on TiO2film in 4 hours. The dye adsorbing, electrolyte filling and cell sealing have been carried out in inert gas atmosphere using a glove box. By new fabrication procedure the energy conversion efficiency (η) of DSCs was improved on 10%. In addition, DSCs fabricated by new procedure were more stable under outdoor testing, the efficiency was even increased 9% at 14-day-outdoor-exposure. From 30thday of outdoor test the cell efficiency began slightly decrease, and reached the initial value after 100-day-exposure. The effect of co-adsorption with chenodeoxycholic acid (CDA) on DSC performance based on new fabrication procedure was investigated. By addition of 100 mM CDA the short circuit photocurrent has significantly increased, the open circuit voltage slightly increased, and the overall power conversion efficiency of as-prepared DSCs was improved by 8%. However the effect of CDA on cell performance was diminished during outdoor exposure. The change of DSC characteristics was discussed based on analysis of electrochemical impedance spectroscopy (EIS) data. The enhancement of photocurrent caused by the photo-activation of the cathode interface during first weeks of outdoors exposure, as well was the effect of co-adsorbate, were interpreted from impedance spectra.

Charge Transport through Organic Molecular Wires Embedded in Ultrathin Insulating Inorganic Membrane

A hybrid organic-inorganic membrane for facilitating artificial photosynthesis is made by embedding surface bound molecular wires in an inorganic ~2 nm thick silica layer by low temperature atomic layer deposition. This membrane is meant to facilitate electron and proton transport between water oxidation and carbon dioxide reaction sites while blocking products and intermediate reactions by compartmentalizing the reaction microenvironments. Here the membrane is studied in a flat form as an intermediate step towards a working artificial photosynthesis system. The membrane is characterized using FT-IR, XPS and EDS-STEM, confirming the wires are intact and embedded in silica. Charge transport through the wires is confirmed by directly measuring the short circuit photocurrent generated by hole injection from a Ru based dye solution while at the same time blocking charge transport from Sn based dye solution which does not have the proper energy level alignment to inject charges to the wires. The incorporation of a molecular wire in an inorganic matrix may facilitate the incorporation of other molecular electronic building block and enable their use in other applications and fields of study.

Influences of Sr-Incorporated TiO2 Layer on the Photovoltaic Properties of Dye-Sensitized Solar Cells.

Effects of a mixed overlayer composed of TiO2 and TiSrO3 on the performance of dye-sensitized solar cells (DSSCs) were investigated. The surface of TiO2 photoelectrode formed on F-doped SnO2 (FTO) was modified by soaking it in a TiCl4:SrCl2 mixed aqueous solution with various molar ratios and then calcining to produce the TiCl4:SrCl2-treated TiO2 photoelectrode (Ti:Sr-TiO2/FTO). The highest power conversion efficiency (PCE) was obtained from DSSC with Ti:Sr(7:3)-TiO2/FTO, which was prepared from the mixed solution with the molar ratio of 7:3 (TiOl4:SrCl2). An enhancement in short-circuit photocurrent (J(sc)) and open-circuit voltage (V(oc)) of DSSC with Ti:Sr(7:3)-TiO2/FTO was achieved, compared to those of the reference device with Ti:Sr(10:0)-TiC2/FTO (i.e., TiO2-coated TiO2/FTO). The incorporation of the mixed overlayer on the nanoporous TiO2 photoelectorde led to an improvement in the electron collection efficiency by a prolonged electron lifetime, thereby increasing the J(sc) value. The increase in V(oc) value of the device with Ti:Sr(7:3)-TiO2/FTO was due to the suppression of the charge recombination between injected electrons and I3(-) ions.

Pyrolysis preparation of WO3 thin films using ammonium metatungstate DMF/water solution for efficient compact layers in planar perovskite solar cells**Project supported by the National Natural Science Foundation of China (Nos. 51472071, 512720616, 51072043), and the National Basic Research Program of China (No. 2011CBA00700).

The tungsten trioxide (WO3) thin films were firstly prepared by spin-coating-pyrolysis methods using the ammonium metatungstate ((NH4)6H2W12O40) DMF/water solution, and successfully applied as the efficient compact layers for the planar perovskite solar cells. The influence of the WO3 film thickness and the rinsing treatment of CH3NH3PbI3 thin film with isopropanol on the photovoltaic performance of the corresponding perovskite solar cells was systematically investigated. The results revealed that the perovskite solar cell with a 62 nm thick WO3 compact layer achieved a photoelectric conversion efficiency of 5.72%, with a short circuit photocurrent density of 17.39 mA/cm2, an open circuit voltage of 0.58 V and a fill factor of 0.57. The photoelectric conversion efficiency was improved from 5.72% to 7.04% by the isopropanol rinsing treatment.

W-doped TiO2 photoanode for high performance perovskite solar cell

Titanium dioxide (TiO2) with dispersed W-doping shows its capability for efficient electron collection from perovskite to TiO2 in perovskite solar cell. The conduction band (CB) of TiO2 moves downward (positive shift) with increasing the tungsten (W) content, which enlarges the energy gap between the CB of TiO2 and the perovskite. Thus, the efficiency of electron injection from perovskite to TiO2 is increased. Due to the increased electron injection, W-doped TiO2 (≤0.2%W content) enhances the short-circuit photocurrent (Jsc) of perovskite solar cell and improves the performance of perovskite solar cell. Perovskite solar cell with 0.1% W-doped photoanode obtains the highest power conversion efficiency (η=10.6%), which shows enhancement by 13% in Jsc and by 17% in η, as compared with the undoped TiO2 perovskite solar cell.