Improvement Of Photovoltaic Performance Research Articles

Modulated CH3NH3PbI3\u2212xBrx film for efficient perovskite solar cells exceeding 18%

The organic-inorganic lead halide perovskite layer is a crucial factor for the high performance perovskite solar cell (PSC). We introduce CH3NH3Br in the precursor solution to prepare CH3NH3PbI3−xBrx hybrid perovskite, and an uniform perovskite layer with improved crystallinity and apparent grain contour is obtained, resulting in the significant improvement of photovoltaic performance of PSCs. The effects of CH3NH3Br on the perovskite morphology, crystallinity, absorption property, charge carrier dynamics and device characteristics are discussed, and the improvement of open circuit voltage of the device depended on Br doping is confirmed. Based on above, the device based on CH3NH3PbI2.86Br0.14 exhibits a champion power conversion efficiency (PCE) of 18.02%. This study represents an efficient method for high-performance perovskite solar cell by modulating CH3NH3PbI3−xBrx film.

Structure-Property Relations of Methylamine Vapor Treated Hybrid Perovskite CH3NH3PbI3 Films and Solar Cells.

The power conversion efficiency of halide perovskite solar cells is heavily dependent on the perovskite layer being sufficiently smooth and pinhole-free. It has been shown that these features can be obtained even when starting out from rough and discontinuous perovskite film by briefly exposing the film to methylamine (MA) vapor. The exact underlying physical mechanisms of this phenomenon are, however, still unclear. By investigating smooth, MA treated films based on very rough and discontinuous reference films of methylammonium triiode (MAPbI3) and considering their morphology, crystalline features, local conductive properties, and charge carrier lifetime, we unraveled the relation between their characteristic physical qualities and their performance in corresponding solar cells. We discovered that the extensive improvement in photovoltaic performance upon MA treatment is a consequence of the induced morphological enhancement of the perovskite layer together with improved electron injection into TiO2, which in fact compensates for an otherwise compromised bulk electronic quality simultaneously caused by the MA treatment.

SWCNT-TiO2 Nanocomposite Photo-Anode for Improved Thermal Performances of Dye-Sensitized Solar Cells

In this study, we report a novel single-wall carbon nanotube (SWCNT)-TiO2 composite photoanode with enhanced thermal conductivity for photovoltaic applications. Thermal chemical vapor deposition technique was used for the growth of high quality SWCNTs. Structural and morphological properties of as synthesized SWCNT and SWCNT-TiO2 composites were inspected using ultra-high resolution transmission electron microscope (UHRTEM) and Raman spectroscopy. Thermal conductivity of pure titania (TiO2) and SWCNT-TiO2 composites were estimated by an optothermal method. Photovoltaic performance of Dye-sensitized solar cell (DSSC) containing composite photoanodes was studied at various temperatures (ranging from room temperature-323K). We observed a notable decline in the overall photovoltaic performance of the DSSC containing pure TiO2 photoanode at elevated temperatures. Whereas, DSSC with composite photoanodes showed a significant improvement in overall photovoltaic performance consistently at room temperature as well as at elevated temperatures that is believed to be due to the existence of SWCNT and provides a conducting pathway to electrons in trap states and which are released at higher temperature and thus, quench recombination more effectively.

Stability Improvement of Photovoltaic Performance in Antimony Sulfide-Based Hybrid Solar Cells

Sb2S3-based hybrid solar cells were prepared in the combination with electron transporting layer of TiO2 or ZnO nanoparticles in addition to poly(3-hexylthiophene)-2,5-diyl/(3, 4-ethylenedioxythiophene): poly(styrene sulfonate), zinc phthalocyanine (ZnPc), or MoO3 for hole transporting layer. Photovoltaic performance and durability of the hybrid solar cells were compared each other with or without encapsulation by using glass and UV cutoff film. Among these hybrid solar cells, it was found that a combination of glass-ITO/TiO2/Sb2S3/ZnPC/Au encapsulated with glass and UV cut filter has the highest durability with keeping the relative power conversion efficiency of 90% through the stability test under 1 sun at 63°C at a relative humidity of 50% for 1,500 h.

Performance of inverted polymer solar cells with randomly oriented ZnO nanorods coupled with atomic layer deposited ZnO

Nanostructuring of the electron transport layer (ETL) in organic photovoltaic cells (OPV) is of great interest because it increases the surface area of the cell and electron transport. In this work, hydrothermally grown, randomly oriented, and low areal density ZnO nanorods (NRs) have been adopted as the ETL, and the effect of adding atomic layer deposited (ALD) ZnO on the ZnO NRs on the inverted organic solar cell performance has been investigated. The fabricated inverted organic solar cell with 5-nm-thick ALD-ZnO grown on the ZnO NRs showed the highest power conversion efficiency (PCE) of 3.08%, which is an enhancement of 85% from that of the cell without ALD-ZnO (PCE=1.67%). The ultrathin ALD-ZnO was found to act as a curing layer of the surface defects on the hydrothermally grown ZnO NRs, resulting in an improvement in photovoltaic performance.

Dual substitution at 4,9-positions of carbazole in donor-π-acceptor copolymer enhances performance of bulk-heterojunction organic solar cells

Several carbazole-2,7-diyl units with alkoxy substituents at the 4-position in addition to branched (1-alkyl)alkyl substituents at the 9-position were developed and combined with difluorinated dithienylbenzothiadiazole by using a Suzuki coupling reaction to synthesize donor–π–acceptor-type copolymers. X-ray diffraction analyses of these copolymers revealed that the 4,9-disubstituted carbazole unit contributed to form a balanced interdigitated structure, which resulted in smaller π-stacking distances (4.0–3.5 Å) of the polymer backbone, a narrower bandgap (2.0–1.8 eV), and higher hole mobilities (4.2 × 10−4 to 2.9 × 10−3 cm2 V−1 s−1) than those of the carbazole copolymer without the 4-substituent (PCDT2FBT). A bulk heterojunction organic photovoltaic device with a configuration of ITO/PEDOT:PSS/polymer:PC70BM/LiF/Al exhibited a power conversion efficiency of 5.46%, a short-circuit current density of 12.4 mA cm−2, a fill factor of 0.58, and an open-circuit voltage of 0.76 V. The photovoltaic performance was much higher than that of PCDT2FBT. These results demonstrate that incorporation of the side chains into the 4,9-positions of carbazole is a novel approach to obtain self-organizing carbazole polymers, enabling improvement in light absorption, hole mobility, and photovoltaic performance.

The effect of tuning chemical structure on the open‐circuit voltage and photovoltaic performance of narrow band‐gap polymers

ABSTRACTMost of the narrow band‐gap polymers exhibit low open‐circuit voltage (Voc) which limits the further improvement of photovoltaic performance. How to improve the Voc through fine tuning of the chemical structure is a significant project that worth exploring. As a big and strong electron accepting unit, fluorinated‐quinoxaline based copolymers always show a narrow band gap and broad absorption which makes it a good template to study the changes of Voc through structure tuning. In this work, the effect of the subtle chemical structure modulation of polymer side chains and main chain on the Voc and photovoltaic performance was investigated. The Voc was adjusted effectively, and the power conversion efficiency (PCE) also was improved simultaneously. Although the PCE was not high enough as those high‐performance polymers reported at present, the result indicates that fine tuning of chemical structure is an effective way to improve Voc and photovoltaic performance for narrow band‐gap polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 699–706

Strategy to Manipulate Molecular Orientation and Charge Mobility in D–A Type Conjugated Polymer through Rational Fluorination for Improvements of Photovoltaic Performances

Improving the photoelectric conversion efficiency of organic solar cells (OSCs) is an essential issue for large scale commercial applications. Introducing the fluorine (F) atoms onto the electron-accepting unit and/or electron-donating unit on donor (D)–acceptor (A) type conjugated polymer is an effective strategy to enhance the overall solar cell performance. Here, the optimum sites for fluorination in favor of boosting the optical and photovoltaic properties of polymers are fully investigated by density functional theory (DFT) calculation and molecular dynamics (MD) simulation. Especially, the interchain charge mobility is calculated by means of Marcus theory, to investigate the charge transport process quantitatively. The results of theoretical modeling indicate that, except for the enhanced absorption spectra and deep lying HOMO level, more importantly, a higher hole mobility could be achieved when F is introduced onto the 3,6 position (outer site) of quaterthiophene for two reasons: (1) more effectiv...

Preparation and improvement in photovoltaic performance of dye-sensitized solar cells using carbon dioxide

We report preparation and improvement in photovoltaic performance of N719-based dye-sensitized solar cells (DSSCs) using pressurized carbon dioxide (CO2) as a co-solvent for the absorption process on the TiO2 photoelectrode surface. Effective absorption of the N719 molecules on the TiO2 surface was achieved using CO2 processing, and the absorption time was shortened drastically from 24 h (in the dip process) to less than 3 h. The cells prepared under pressurized CO2 for the absorption showed greater photovoltaic performance, especially higher short-circuit current density and conversion efficiency, compared with that from typical dip method. It was revealed that the suitable CO2 pressure for the absorption was 5 MPa and the efficiency was achieved to be more than 7.5 %. Prevention of back electron transfer reactions from TiO2 to oxidized dyes or iodides was caused currently, because the homogeneous coverage of N719 molecules on the TiO2 surface was obtained by the use of pressurized CO2.

Improvement of photovoltaic performance of perovskite solar cells with a ZnO/Zn2SnO4 composite compact layer

In this study, ZnO/Zn2SnO4 (ZSO) composite is synthesized as a promising alternative compact layer to TiO2 by spray pyrolysis method. Owing to the ZnO/ZSO composite possesses higher carrier mobility and suitable band gap structure, it will behave well in the application of solar cells. The characterization results show that the ZnO/ZSO composite compact layer manifests better optical transmittance, enhanced electrons collective efficiency and superior electrical conductivity. Consequently, the corresponding photo-current is improved effectively when compared with that of TiO2 compact layer. The optimum efficiency of perovskite solar cell based on the ZnO/ZSO composite compact layer reaches 12.03% at AM 1.5 solar light of 100mWcm−2, which is 18% higher than that of perovskite solar cell based on the TiO2 compact layer.

Improvement in Photovoltaic Performance of Dye Sensitized Solar Cell Using Activated Carbon-TiO2Composites-Based Photoanode

In this study, the activated carbon (AC) is synthesized from the oil fly ash (FA). Noncarbonaceous impurities were eliminated by acidic treatment of oil FA. Brunauer–Emmett–Teller and scanning electron microscopy energy-dispersive spectroscopy (SEM-EDS) analyses are used to characterize the AC. The AC is then mixed with TiO2 in different concentrations to form hybrid photoanodes for dye sensitized solar cells. The dispersion of AC in TiO2 is confirmed by transmission electron microscopy analysis. Solar cells are fabricated by employing the composite films as the working electrode. The UV-Visible absorption spectroscopy, photocurrent–voltage characteristic and electrochemical impedance spectroscopy analyses are carried out to examine the performance of solar cells. The results indicate that the concentration of AC in photoanode strongly affects the efficiency of solar cells. The solar cell fabricated with 0.05% AC -TiO2 photoanode, shows the highest efficiency of 5.45%, which is 61% greater than unmodified photoanode (3.38%). Density functional theory quantum modeling technique is used to compute the band gap of TiO2 and C-TiO2 clusters.

SWCNT-TiO2 Nanocomposite Photo-Anode for Improved Thermal Performances of Dye-Sensitized Solar Cells

In this study, we report a novel single-wall carbon nanotube (SWCNT)-TiO2 composite photoanode with enhanced thermal conductivity for photovoltaic applications. Thermal chemical vapor deposition technique was used for the growth of high quality SWCNTs. Structural and morphological properties of as synthesized SWCNT and SWCNT-TiO2 composites were inspected using ultra-high resolution transmission electron microscope (UHRTEM) and Raman spectrosctopy. Thermal conductivity of pure titania (TiO2) and SWCNT-TiO2 composites were estimated by an optothermal method. Photovoltaic performance of Dye-sensitized solar cell (DSSC) containing composite photoanodes was studied at various temperatures (ranging from room temperature-323K). We observed a notable decline in the overall photovoltaic performance of the DSSC containing pure TiO2 photoanode at elevated temperatures. Whereas, DSSC with composite photoanodes showed a significant improvement in overall photovoltaic performance consistently at room temperature as well as at elevated temperatures that is believed to be due to the existence of SWCNT and provides a conducting pathway to electrons in trap states and which are released at higher temperature and thus, quench recombination more effectively.

Prospects of conducting polymer and graphene as counter electrodes in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) garner considerable research interest because of high photo-to-electric conversion efficiencies at low production cost. Platinum has been reported as an efficient metal as a counter electrode (CE) in DSSCs for its outstanding electro catalytic performance. However, the high cost and susceptibility to corrosion of Pt are paving the way for exploring new materials to replace Pt as a counter electrode in DSSCs. Various conducting polymers, graphene and conducting polymer-graphene nanocomposites have been found as counter electrodes in DSSCs with remarkable photovoltaic performances. The urge to produce composites or hybrids with nanomaterials is derived from the improvement of photovoltaic performances. This review will focus on the unique physical and chemical properties of conducting polymers and graphene, their individual photovoltaic performances as counter electrodes in DSSCs, followed by the synergistic effect of conducting polymers and graphene in conducting polymer-graphene nanocomposites as counter electrodes in DSSCs. Finally a brief outlook is provided to improve the photovoltaic performance of DSSCs using conducting polymers and graphene-based counter electrodes.

Interface studies of the planar heterojunction perovskite solar cells

Planar perovskite solar cells (PSCs) with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have attracted much interest because they can be fabricated by low temperature process and exhibit high power conversion efficiency (PCE). The PCE is strongly dependent on the interface properties between the PCBM layer and cathode. In this work, solution-processable material, rhodamine 101, was used as the interfacial layer between the PCBM layer and Ag cathode. These interfacial materials significantly increase the fill factor so as to the PCE of the PSCs. The optimal power conversion efficiencies are 13.2% (CH3NH3PbI3) and 14.8% (CH3NH3PbI3−xClx) for the devices with rhodamine 101 as the electron collection interlayer, saliently higher than that (8.5% and 12.0%) of control devices without an electron-collection interlayer. The effect of the interfacial material is carefully examined by time-resolved photoluminance spectroscopy (TR-PL), ultraviolet photoelectron spectroscopy (UPS), and kelvin probe force microscopy (KPFM) techniques. Decreased work-function and energy barrier, enhanced electron extraction and prolonged free carrier lifetime all contributed to the photovoltaic performance improvement.

Interfacial quality improvement of Cu(In,Ga)Se2 thin film solar cells by Cu-depletion layer formation

Se irradiation with time, tSe, was introduced after the second stage of a three-stage process to control the Cu2Se layer during Cu(In,Ga)Se2 (CIGS) deposition. Open circuit voltage and fill factor of CIGS solar cells could be improved by introducing Se irradiation. We concluded that the control of the Cu2Se layer led to the formation of a Cu-depletion CIGS layer (CDL), which improved conversion efficiency owing to suppression of interfacial recombination by a valence band offset formed between CIGS and the CDL. Finally, highest efficiency of 19.8% was achieved with tSe of 5 min. This very simple and new technique is promising for the improvement of photovoltaic performance.

Improvement of photovoltaic performance of inverted hybrid solar cells by adding single-wall carbon nanotubes in poly(3-hexylthiophene)

Solution prepared hybrid solar cells show promising low cost technology for electricity generation from sun light, although their power conversion efficiency has to be improved. One of the approaches is to increase the absorbance or charge carrier mobility of organic semiconductors. In this work, pristine single walled carbon nanotubes (SWCNT) were added into poly(3-hexylthiophene) (P3HT) solution to form P3HT:SWCNT composite films with different weight percent (wt%) of SWCNT. It is observed that optical absorbance spectra as well as the morphology of the composite films were modified by the addition of SWCNTs. This phenomenon could be explained by the π-π interaction between the conjugated polymer and carbon nanotubes. Most importantly, the electrical conductivities of the composite films increased with the SWCNT wt%. When these films were used as hole conductor layers in inverted planar hybrid solar cell, with CdS thin films as electron acceptor layers, the fill factor (FF) and open-circuit voltage (Voc) of the corresponding cells were decreased with the increase of the wt% of SWCNT. However, the short-circuit current density (Jsc) and the power conversion efficiency (PCE) showed a maximum value at about 0.4wt% of SWCNT in P3HT. The transient photovoltage measurements (TPV) revealed that the presence of SWNCT promoted the charge recombination process at P3HT/CdS interface, and as a result, reduced the Voc. The photovoltaic performance of the hybrid solar cells could be optimized by choosing an adequate weight percentage of SWCNT in P3HT to balance the charge carrier transport and charge recombination processes at the donor-acceptor interface.

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.

Petascale Simulations of the Morphology and the Molecular Interface of Bulk Heterojunctions.

Understanding how additives interact and segregate within bulk heterojunction (BHJ) thin films is critical for exercising control over structure at multiple length scales and delivering improvements in photovoltaic performance. The morphological evolution of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blends that are commensurate with the size of a BHJ thin film is examined using petascale coarse-grained molecular dynamics simulations. Comparisons between two-component and three-component systems containing short P3HT chains as additives undergoing thermal annealing demonstrate that the short chains alter the morphology in apparently useful ways: they efficiently migrate to the P3HT/PCBM interface, increasing the P3HT domain size and interfacial area. Simulation results agree with depth profiles determined from neutron reflectometry measurements that reveal PCBM enrichment near substrate and air interfaces but a decrease in that PCBM enrichment when a small amount of short P3HT chains are integrated into the BHJ blend. Atomistic simulations of the P3HT/PCBM blend interfaces show a nonmonotonic dependence of the interfacial thickness as a function of number of repeat units in the oligomeric P3HT additive, and the thiophene rings orient parallel to the interfacial plane as they approach the PCBM domain. Using the nanoscale geometries of the P3HT oligomers, LUMO and HOMO energy levels calculated by density functional theory are found to be invariant across the donor/acceptor interface. These connections between additives, processing, and morphology at all length scales are generally useful for efforts to improve device performance.

Optimizing the performance of inverted type hybrid organic solar cell based on ZnO/P3HT with various polymer deposition parameters

Various polymer deposition parameters have been investigated to improve the overall performance of the inverted type hybrid organic solar cells based on zinc oxide (ZnO)/poly(3-hexylthiophene) (P3HT). The polymer was deposited onto fluorine-doped tin oxide/ZnO nanorod arrays (NRAs) substrates via spin coating technique and followed by deposition of silver (Ag) using electron gun evaporation technique to build the devices. The objective of this work is to achieve the optimum device performance by selecting the best polymer concentration (25–40 mg/ml), spin coating speed (500–2000 rpm) and diluted polymer concentration (1–4 mg/ml) for ZnO NRAs surface modification. Experimental results showed that the device with P3HT concentration of 35 mg/ml, spin coating speed of 1000 rpm and ZnO NRAs surface modification with 1 mg/ml diluted P3HT solution exhibited the highest power conversion efficiency of 0.27 %. The surface roughness, P3HT top layer thickness and P3HT infiltration contributed to the significant photovoltaic performance improvement.

The control of surface texture for planar CH3NH3PbI3−xClx film and its effect on photovoltaic performance

The surface texture with a long alignment was observed on the surface of CH3NH3PbI3−xClx films prepared using one-step solution deposition. We found that it appears only when hydroiodic acid with stabilizer H3PO2 is adopted to prepare CH3NH3I powder. However, even with this stabilizer, the surface texture of CH3NH3PbI3−xClx films can also be eliminated completely by sufficiently lateral diffusion before annealing, which can be achieved by high speed coating above 3000 rpm or drying for 30 min at room temperature. The later process results in a smooth surface with homogeneous grains and hence the improvement of photovoltaic performance.