Significant Improvement In Photovoltaic Performance Research Articles

Analysis molecular design of novel D-A-Di-A-D conjugated compounds for high-efficiency organic solar cells.

The work described in this section uses DFT/TD-DFT/B3LYP/6-31G (d,p) (density functional theory and time-dependent density functional theory) to study and simulate the structural, optoelectronic, and optical properties of a series of conjugated compounds based on a modular D-A-Di-A-D architecture. These compounds integrate the D donor unit (carbazole), the A acceptor unit (benzothiadiazole) and various Di donor units. Using AMPS-1D (analysis of micronic structure and photonics), work has been carried out to evaluate the photovoltaic performance of these conjugated compounds in the context of organic solar cells. The compounds show variable performance in terms of energy conversion efficiency, ranging from 7.11 to 11.70%. The addition of a PEDOT layer between the active layer and the anode results in a significant improvement in photovoltaic performance, with energy conversion efficiencies of up to 15.31%, the highest value achieved. The use of ZnO as an intermediate layer remarkably improves photovoltaic performance for all compounds, with notable energy conversion efficiencies reaching 17.13%, 17.20%, and 18%. All in all, the compounds studied present promising prospects as viable candidates for organic block heterojunction (BHJ) solar cell applications. DFT/TD-DFT/B3LYP/6-31G (d,p), these acronyms stand for the computational methods used to study the properties of compounds. DFT, for "Density Functional Theory", is a quantum computation method used to describe the electronic and structural properties of molecular systems. TD-DFT, for "Time-Dependent Density Functional Theory", is an extension of DFT that allows the treatment of optical and excitation properties. B3LYP is a density functional frequently used in DFT to calculate molecular properties. In addition, 6-31G (d,p) refers to a basic wave function used to approximate the distribution of electrons in molecules. AMPS-1D, or "Analysis of Micro and Photonic Structure", is a modeling tool for studying the photovoltaic properties of multilayer structures, particularly in the context of organic solar cells.

Cascade Förster Resonance Energy Transfer Studies for Enhancement of Light Harvesting on Dye-Sensitized Solar Cells.

This work reports cascade Förster resonance energy transfer (FRET)-based n-type (ZnO) and p-type (NiO) dye-sensitized solar cells (DSSCs), discussing approaches to enhance their overall performance. Although DSSCs suffer from poorer performance than other solar cells, the use of composites with carbon dot (Cdot) can enhance the power conversion efficiency (PCE) of DSSCs. However, further improvements are demanded through molecular design to stimulate DSSCs. Here, a photosensitized system based on a cascade FRET was induced alongside the conventional photosensitizer dye (N719). To N719 in a DSSC is transferred the energy cascaded through donor fluorescence materials (pyrene, 3-acetyl-7-N,N-diethyl-coumarin or coumarin and acridine orange), and this process enhances the light-harvesting properties of the sensitizers in the DSSC across a broad region of the solar spectrum. PCE values of 10.7 and 11.3% were achieved for ZnO/Cdot and NiO/Cdot DSSCs, respectively. These high PCE values result from the energy transfer among multi-photosensitizers (cascade FRET fluorophores, N719, and Cdot). Moreover, Cdot can play a role in intensifying the adsorption of dyes and discouraging charge recombination on the semiconductor. The present results raise expectations that a significant improvement in photovoltaic performance can be attained of DSSCs exploiting the cascade FRET photonics phenomenon.

Fluorination of the π-bridge in a polymer skeleton enables a significant improvement in photovoltaic performance

An easy and efficient approach for the synthesis of an important photoelectric intermediate 3-fluoro-2-iodithiophene is developed. Therefrom, a polymer J52FF, featuring fluorination of the π-bridges on the backbone and side chains of the classical polymer, J52, is synthesized. J52FF displays a coplanar molecular configuration with the dihedral angles smaller than 2° in skeleton, a low-lying HOMO energy level of −5.62 eV, which is nearly aligned with the acceptor IT-4F, and a broad absorption range from 300 nm to 650 nm. The J52FF:IT-4F (1:0.8) blend shows a strong and complementary spectral absorption, a uniform fibrillar textured morphology and high and balanced charge mobilities. The inverted device based on J52FF:IT-4F blend obtained an encouraging power conversion efficiency (PCE) of 14.83% with the open-circuit voltage (Voc) of 0.90 V, the short circuit current (Jsc) of 23.21 mA cm−2, and the fill factor (FF) of 0.71 under the optimal conditions, which is one of the best PCE value among the ever reported BDT-alt-BTz derivatives or IT-4F based non-fullerene organic solar cells (NF–OSCs). It demonstrates that fluorination of polymer in skeleton is an efficient strategy for obtaining high performance.

Enhanced efficiency of low-temperature fabricated dye-sensitized solar cells by incorporating upconversion nanoparticles

Upconversion nanoparticles (UCNPs) can effectively assist solar cells in utilizing near infrared through the anti-Stokes’ emission mechanism. We incorporate UCNPs, for the first time, into the mesoporous TiO2 of dye-sensitized solar cells (DSSCs) in a low-temperature fabrication process. The mesoporous TiO2 is designed as a two-layer structure, where the lower layer is prepared from reactive anatase TiO2 chelated by acetic acid (h-TAc). The UCNP incorporation into the lower layer displays a significant improvement in photovoltaic performance. For an optimized UCNP incorporation, the power conversion efficiency (PCE) of the DSSCs can increase from 6.49 to 7.98%, an enhancement of 23%, further exceeding most of the improvement on low-temperature fabricated DSSCs reported in the literature. The enhanced PCE may be ascribed to the increase of photocurrent. We find that the hydrophobic UCNPs reveal better enhancement than hydrophilic UCNPs due to the prevention from the electrolyte penetration. However, the hydrophobic UCNP incorporation may cause the cracking of the mesoporous TiO2 layer. The strong bonding ability of h-TAc effectively alleviates the cracking issue.

High-performance and stable inverted perovskite solar cells using low-temperature solution-processed CuNbOx hole transport layer

For a typical perovskite solar cell (PSC), the hole transport layer (HTL) plays a vital role in determining device performance and stability. Herein, for the first time, we demonstrate that a low-temperature solution-processed copper-niobium oxide (CuNbOx) thin film, consisting of CuNbO3 and CuNb2O6 phases, can serve as an efficient HTL to develop PSCs with high-performance and long-term stability simultaneously. The CuNbOx thin film possesses high optical transparency in visible light, well-matched energy levels with perovskite, and excellent hole extraction capability from the perovskite layer. By optimizing the precursor concentration, the CuNbOx-based device reaches the best power conversion efficiency (PCE) of 16.01% with negligible hysteresis. In comparison, the control device based on the extensively studied PEDOT:PSS HTL shows an obviously lower PCE of 10.13%. Besides exhibiting significant improvement in photovoltaic performance, our CuNbOx-based device also shows much enhanced long-term stability than the control device. After 1000 h of storage in air without encapsulation, the CuNbOx-based PSCs maintains ~78% of their initial efficiency, whereas the PCE of PEDOT:PSS-based PSCs drops to ~44% of the initial value. Overall, this study suggests that the utilization of the inorganic CuNbOx thin film as the HTL provides a novel route for fabricating low-cost, high-performance, and stable PSCs.

Interface engineering of G-PEDOT: PSS hole transport layer via interlayer chemical functionalization for enhanced efficiency of large-area hybrid solar cells and their charge transport investigation

In this study, in order to minimize the recombination current of free charge carriers in a large-area organic-inorganic hybrid solar cell (O-IHSCs), we improved the electrical conductivity of a graphene (G) and poly(3,4-ethylenedioxy thiophene)–poly(styrenesulfonate) (G-PEDOT:PSS) hole transport layer (HTL) by introducing various concentrations of synthesized graphene (G) into poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The electrical conductivity of G-PEDOT:PSS was enhanced to 932781.17 S m−1 via the addition of 2 mg/mL of G to PEDOT:PSS. The O-IHSCs fabricated with the highly conductive G-PEDOT:PSS composite as HTL enhanced the power conversion efficiency (PCE) to 3.90%, a 70% increase compared to O-IHSCs fabricated with pristine PEDOT:PSS HTL. However, the accumulation of G at a higher concentration (2.5 mg/mL) degrades the performance of the solar cell, which generated further defects or film aggregation, interfering with the fast transport of free charge carriers toward their respective electrodes. The G-PEDOT:PSS composite contained various types of functionalization via interfacial reaction between the G and PEDOT:PSS based on Raman and X-ray photoelectron spectroscopy studies. These chemical functionalizations provide an additional mechanism of charge transport via bridges enhancing the carrier mobility and suppression of recombination of free charge carriers, resulting in significant improvement in photovoltaic performance of the O-IHSCs.

Improved photovoltaic performance of 2,7-pyrene based small molecules via the use of 3-carbazole as terminal unit

Small molecule of Py-2DTBTCz with an Ar(A–D)2 framework was designed and synthesized as photovoltaic donor materials, in which 2,7-pyrene (Py) and benzothiadiazole (BT) were respectively used as central aryl (Ar) and arm acceptor (A), while 3-carbazole (Cz) as terminal donor (D). For comparison, an A–Ar–A type SM of Py-2DTBT without Cz terminal unit was also prepared. The effects of Cz on optical, electrochemical, hole mobility and photovoltaic properties were investigated. In solution-processed solar cells, it was observed that the Py-2DTBTCz based devices show significant improvement in photovoltaic performance compared to those of Py-2DTBT. Power conversion efficiency (PCE) of Py-2DTBTCz could be as high as 2.89% with a short-circuit current density (Jsc) of 7.68 mAcm−2. The results indicate that appending an enlarged Cz π-system to the terminal of A–Ar–A-type small molecules for the construction of an Ar(A–D)2 framework can significantly improve the photovoltaic performance of SMs.

Recent progress in silicon-based solid-state solar cells

ABSTRACTSilicon (Si)-based solar cells constitute about 90% of the photovoltaic (PV) market, and a drastic reduction in module cost and significant improvement in PV performance have been observed since its first inception in 1941. This article aims to present the comprehensive review of prominent advancements enacted in Si solar cells after the year 2000. Monocrystalline Si solar cell has been the matured technology with the record efficiency (η) of 26.6% achieved so far. As the drive to push η around 30% Schokley–Quiesser limit is foreseeable in the near future, PV community is actively striving to fabricate efficient yet cost-effective devices. Polycrystalline Si solar cells contain small-sized grains, and efforts are underway to enhance the η beyond 21.9% by controlling the recombination at grain boundaries, optimising the passivated interfaces and deposition process. Thin-film amorphous Si technology proffers low-cost fabrication process and η of 13.6% has been recorded for a multijunction solar cell. Employment of sophisticated nanowire-based light trapping schemes and dopant-free carrier-selective layers along with the development of hybrid solar cells of organic and Si materials are among the emerging research trends for Si solar cells.

Dye sensitized solar cells using catalytically active CuO-ZnO nanocomposite synthesized by single step method

In the present paper we report a low cost, single step preparation method for the synthesis of CuO-ZnO nanocomposite through simple co-precipitation technique using oxalic acid. To have a better idea about the deviations brought about by the inclusion of CuO in ZnO lattice, pure ZnO nanoparticles synthesized from 0.1M solutions were also investigated. X-ray diffraction studies showed that the composite contains only hexagonal wurtzite ZnO and monoclinic CuO structures. The magnetic studies of CuO-ZnO heterostructures were also conducted in order to elucidate the source of the ferromagnetism observed at room temperature. The catalytic efficiency of the as prepared nanocomposite was estimated by the degradation of methylene blue and eosin yellowish which also shows its suitability as a promising candidate in waste water treatment. The effect of chenodeoxycholic acid as a co-adsorbent in the performance of dye sensitized solar cells fabricated using the synthesized ZnO and the nanocomposite was also studied and significant improvement in photovoltaic performance has been obtained for nanocomposite based solar cell.

An efficient TiO2 electron transport layer for compact TiO2/polycrystalline BiFeO3 heterostructure thin film with enhanced photovoltaic performance

In this letter, high-performance TiO2/BiFeO3 heterostructure thin film is successfully prepared by introducing sol-gel derived-TiO2 (SG-TiO2) electron transport layer. A significant improvement of photovoltaic performance has been achieved. 3.674% power conversion efficiency of the thin film is obtained with open-circuit voltage (Voc) of 1.64 V, short-circuit photocurrent (Jsc) of 3.5 mA/cm2 and fill factor (FF) of 64%, which implies that the introduction of a TiO2 would improve the photovoltaic performance under visible light illumination. Our work demonstrates that the TiO2/BFO heterostructure thin film possesses the potential for better use in the solar energy devices applications.

Translucent TiO2 Nanotube Film for Quantum Dots Sensitized Solar Cells

A translucent TiO2 nanotube film was fabricated as architecture for quantum dots sensitized solar cells (QDSSCs). The CdS quantum dots (QDs) were deposited on this translucent film by successive ionic layer adsorption reaction (SILAR) method. We analyzed the CdS QDs sensitized TiO2 nanotube by SEM and TEM, which proved that this TiO2 nanotube film can absorb QDs for solar cell application. Based on this translucent TiO2 nanotube film, QDSSC which can be illuminated from photoanode was constructed. In comparison with QDSSC based on TiO2 nanotube grown on Ti foil for illuminated from counter electrode, the photoanode illuminated QDSSC shows a significant improvement of photovoltaic performance. The improved result can be ascribed to the contribution of translucent TiO2 NT film, which provides the possibility for photoanode illumination to reduce the loss of light caused by unwanted reflection and absorption.

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.

The role of Na incorporation in the low-temperature processed CIGS thin film solar cells using post deposition treatment

Na incorporation is widely considered to play an important role in low-temperature processed Cu(In,Ga)Se2 (CIGS) solar cells. In this work, we used post deposition treatment (PDT) method for Na incorporation in CIGS films, which involved the deposition of a thin NaF layer accompanied by thermal annealing. It was found that thermal annealing drove the diffusion of Na into CIGS absorbers without causing loss of elements and change of crystallinity. The dependence of the photovoltaic performance and recombination of CIGS solar cells on the Na PDT temperature was investigated. Impedance spectroscopy and admittance spectroscopy were used to characterize the recombination and defects of CIGS solar cells. The results indicated that the CIGS solar cells with Na PDT exhibited significant improvement of photovoltaic performance compared to those with Na-free. The enhanced transport performances of Na-treated cells were attributed to the decreased space-charge region (SCR) recombination. Both Na-free and Na-treated at 300 °C CIGS devices showed a donor defect with activation energy of about 295 meV, while the Na-treated devices demonstrated lower density of states, which resulted in an improved Voc. A maximum conversion efficiency of 11.9% was achieved for CIGS solar cells with Na PDT temperature at 300 °C.

Significant improvement of photovoltaic performance by embedding thiophene in solution-processed star-shaped TPA-DPP backbone

Solution-processed star-shaped triphenylamine (TPA) derivatives and dialkylated diketopyrrolopyrrole (DPP)-based small molecules have been widely studied because they both yield promising photon-to-electron conversion. However, the power conversion efficiency (PCE) of covalent star-shaped TPA-DPP derivatives is still very low. To design star-shaped TPA-DPP derivatives with better photovoltaic performance, we embedded a thiophene ring in between the TPA and DPP units, namely TPA-T-DPP, and reported the comparative studies of the optoelectronic and photovoltaic properties of TPA-DPP and TPA-T-DPP. Benefiting from the covalent thiophene bridges, compared to the TPA-DPP solid film, the TPA-T-DPP film showed enhanced light-harvesting ability, for instance, an improved absorptivity (Abs. = 1.72/100 nm vs. 1.23/100 nm), a broader absorption band (131 nm vs. 107 nm) and a narrower band gap (1.86 eV vs. 1.91 eV), from cyclic voltammetry. Studies on the photovoltaic properties revealed that the best TPA-T-DPP:PC71BM based device showed a dramatically enhanced PCE of 2.95%, increased by 2.14 times with respect to the efficiency of the best TPA-DPP based device (1.38%). The improvement of PCE also was observed in the small molecule:PC61BM based devices (1.81% vs. 1.13%). Test of the hole mobilites of the active layer provided further insight into the impact of the embedded thiophene units. The hole mobility of the TPA-T-DPP:PC71BM blended films was higher by about one order of magnitude (1.16 × 10−2 cm2 V−1 s−1) than that of the TPA-DPP:PC71BM blended films (3.85 × 10−3 cm2 V−1 s−1). These results clearly indicated that embedding the thiophene ring enlarged the conjugation, thus enhanced the light-harvesting ability and hole mobility, while further significantly improving the device performance. Additionally, TPA-T-DPP was also used as the electron-acceptor material, and the best P3HT:TPA-T-DPP based device exhibited a very high open-circuit voltage (1.14 V), which was among the highest values reported for single-layered OSC devices.

Synergistic effects of high temperature and impact compaction on the nano-TiO2 film for the significant improvement of photovoltaic performance of flexible dye-sensitized solar cells

The electron transport property in TiO2 film was investigated to understand the significant improvement of the photovoltaic performance of dye-sensitized solar cells (DSCs) by using in situ substrate heating and in situ particle heating approaches through the vacuum cold spraying technology, which accelerates the powder to impact on the substrate surface and form a film. Results showed that the particle connection and thereby electron transport property in TiO2 film was improved more significantly by in situ particle and substrate heating than by conventional post-sintering of TiO2 film. An equivalent circuit model was proposed to explain the relationship between the short-circuit current density and electron transport property. The result suggested the existence of synergistic effects of high temperature and impact compaction on the nano-TiO2 film in vacuum cold spray process. Furthermore, due to the ability of retaining substrate at a low temperature, in situ particle heating approach could be applied to deposit the TiO2 film for plastic-based flexible solar cells, presenting a high efficiency of 4.4%.

Significant Improvement of Photovoltaic Performance of Dye-sensitized Solar Cells by Using 4-Trimethylsilylpyridine as Organic Additive to Electrolyte Solution

Abstract The applicability of 4-trimethylsilylpyridine (4TMSpy) was investigated as an organic additive to the electrolyte solution of dye-sensitized solar cells. The N3-sensitized solar cell with 4TMSpy showed higher light-to-electric energy conversion efficiencies than that with the ordinary organic additive of 4-tert-butylpyridine by a factor of ca. 1.1. This improvement of the photovoltaic performance was considered to be due to the bulkiness and peculiar electronic properties of the trimethylsilyl group.

Reticulated Organic Photovoltaics

AbstractThis paper shows how the self‐assembled interlocking of two nanostructured materials can lead to increased photovoltaic performance. A detailed picture of the reticulated 6‐DBTTC/C60 organic photovoltaic (OPV) heterojunction, which produces devices approaching the theoretical maximum for these materials, is presented from near edge X‐ray absorption spectroscopy (NEXAFS), X‐ray photoelectron spectroscopy (XPS), Grazing Incidence X‐ray diffraction (GIXD) and transmission electron microscopy (TEM). The complementary suite of techniques shows how self‐assembly can be exploited to engineer the interface and morphology between the cables of donor (6‐DBTTC) material and a polycrystalline acceptor (C60) to create an interpenetrating network of pure phases expected to be optimal for OPV device design. Moreover, we find that there is also a structural and electronic interaction between the two materials at the molecular interface. The data show how molecular self‐assembly can facilitate 3‐D nanostructured photovoltaic cells that are made with the simplicity and control of bilayer device fabrication. The significant improvement in photovoltaic performance of the reticulated heterojunction over the flat analog highlights the potential of these strategies to improve the efficiency of organic solar cells.

Novel branched coumarin dyes for dye-sensitized solar cells: significant improvement in photovoltaic performance by simple structure modification

The construction of branched coumarin dyes based on a 2D-π-A system is focused to optimize the light-harvesting capability and enhance the photovoltaic performance. Three novel coumarin dyes, coded as MS-C, MS-F, and MS-M, respectively, were obtained by incorporating different units (carbazole, fluorene and methyl groups) with different molecular volume and degrees of electron-donating capability into the π-conjugation linker. Through molecular engineering, their light-harvesting capabilities, energy levels and photovoltaic performance were studied systematically. As expected, with the additional donor, especially utilizing strong electron-donating carbazole unit, the IPCE action spectrum of MS-C keeps a high plateau from 390 nm to 580 nm with nearly unity values. Along with the improvement of IPCE, the Jsc values of the three dyes were increased by 77% from 7.61 (MS-M) to 13.47 mA cm−2 (MS-C). Using DCA as the co-adsorbed material, the Jsc of MS-M was increased while these values were decreased in the cases of branched MS-C and MS-F. This means that the twist structure arising from the branched donors could prevent π-aggregation effectively. More importantly, the Voc was also improved significantly by introducing the additional donor. While the branched 2D-π-A system was constructed, the Voc was sharply increased from 508 (MS-M) to 610 mV (MS-C). Comprehensively, a more than 100% enhancement in overall conversion efficiency (5.53%) was realized by branched MS-C compared to the linear MS-M (2.74%). Although the overall conversion efficiencies of these dyes are not very high, these results will still afford significant value for future development of efficient coumarin sensitizers with high open-circuit voltage.