Output Power Conversion Efficiency Research Articles

Synergistic effect of TiO2 hierarchical submicrospheres for high performance dye-sensitized solar cells

The performance of dye-sensitized solar cells (DSCs) could be improved by using rationally designed mesoporous film structure for electron collection, dye adsorption and light scattering. The development of a novel double layer film prepared by TiO2 hierarchical submicrospheres and nanoparticles was reported in this article. The submicrospheres were composed of rutile nanorods of 10 nm diameter and the length of 150–250 nm, which facilitated fast electron transport, charge collection and light scattering. Using a double layer structure consisting of the 10 wt% film as a dye loading layer and the 50 wt% film as the light scattering layer, C101 sensitizer and liquid electrolyte, DSC yielded power conversion efficiency of 9.68% under 1 sun illumination.

Rhodanine flanked indacenodithiophene as non-fullerene acceptor for efficient polymer solar cells

A fused-ring electron acceptor IDT-2BR1 based on indacenodithiophene core with hexyl side-chains flanked by benzothiadiazole rhodanine was designed and synthesized. In comparison with its counterpart with hexylphenyl side-chains (IDT-2BR), IDT-2BR1 exhibits higher highest occupied molecular orbital (HOMO) energy but similar lowest unoccupied molecular orbital (LUMO) energy (IDT-2BR1: HOMO=−5.37 eV, LUMO=−3.67 eV; IDT-2BR: HOMO=−5.52 eV, LUMO=−3.69 eV), red-shifted absorption and narrower bandgap. IDT-2BR1 has higher electron mobility (2.2×10–3 cm2 V–1 s–1) than IDT-2BR (3.4×10–4 cm2 V–1 s–1) due to the reduced steric hindrance and ordered molecular packing. Fullerene-free organic solar cells based on PTB7-Th:IDT-2BR1 yield power conversion efficiencies up to 8.7%, higher than that of PTB7-Th:IDT-2BR (7.7%), with a high open circuit voltage of 0.95 V and good device stability.

Integrated planar and bulk dual heterojunctions capable of efficient electron and hole extraction for perovskite solar cells with >17% efficiency

To achieve high-performing perovskite solar cells (PSCs) interfacial engineering of the perovskite thin film and charge carrier-selective layers is vital for fast extraction of photogenerated electrons and holes, and the suppression of electron-hole recombination. Herein, a glucose-assisted self-assembly solvothermal protocol is reported to prepare electron-rich TiO2 thin films as effective electron transport layers exhibiting enhanced electron mobility. Bilayer structured CH3NH3PbI3 perovskite films are spontaneously formed, consisting of a flat and dense bottom layer forming the TiO2/CH3NH3PbI3 planar heterojunction and a textured and porous top layer elongating in the vertical direction forming the CH3NH3PbI3/spiroMeOTAD bulk heterojunction. The integrated planar and bulk dual heterojunction based PSCs are efficient in light harvesting and charge collection, and thus yield power conversion efficiencies up to 17.75% and a stabilized power output above 17.20%. Integrating both planar and bulk heterojunctions into a PSC assembly provides an effective approach for fabricating highly efficient perovskite optoelectronic devices.

Fluorine-containing low-energy-gap organic dyes with low voltage losses for organic solar cells

Fluorine-containing donor molecules TFTF, CNTF and PRTF are designed and isomer selectively synthesized for application in vacuum‍-deposited organic solar cells. These molecules comprise a donor‍-‍acceptor molecular architecture incorporating thiophene and benzothiadiazole derivatives as the electron-‍donating and electron-‍withdrawing moieties, respectively. As opposed to previously reported materials from this class, PRTF can be purified by vacuum sublimation at moderate to high yields because of its higher volatility and better stabilization due to a stronger intramolecular hydrogen bond, as compared to TFTF and CNTF. The UV-‍vis absorption spectra of the three donors show an intense broadband absorption between 500nm and 800nm with similar positions of their frontier energy levels. The photophysical properties of the three donor molecules are thoroughly tested and optimized in bulk heterojunction solar cells with C60 as acceptor. PRTF shows the best performance, yielding power conversion efficiencies of up to 3.8%. Moreover, the voltage loss for the PRTF device due to the non-‍radiative recombination of free charge carriers is exceptionally low (0.26V) as compared to typical values for organic solar cells (>0.34V).

Effective Ligand Engineering of the Cu2ZnSnS4 Nanocrystal Surface for Increasing Hole Transport Efficiency in Perovskite Solar Cells

Effective engineering of surface ligands in semiconductor nanocrystals can facilitate the electronic interaction between the individual nanocrystals, making them promising for low‐cost optoelectronic applications. Here, the use of high purity Cu2ZnSnS4 (CZTS) nanocrystals as the photoactive layer and hole‐transporting material is reported in low‐temperature solution‐processed solar cells. The high purity CZTS nanocrystals are prepared by engineering the surface ligands of CZTS nanocrystals, capped originally with the long‐chain organic ligand oleylamine. After ligand removal, CZTS nanocrystals show substantial improvement in photoconductivity and mobility, displaying also an appreciable photoresponse in a simple heterojunction solar cell architecture. More notably, CZTS nanocrystals exhibit excellent hole‐transporting properties as interface layer in perovskite solar cells, yielding power conversion efficiency (PCE) of 15.4% with excellent fill factor (FF) of 81%. These findings underscore the importance of removing undesired surface ligands in nanocrystalline optoelectronic devices, and demonstrate the great potential of CZTS nanocrystals as both active and passive material for the realization of low‐cost efficient solar cells.

From Fluorine to Fluorene—A Route to Thermally Stable aza‐BODIPYs for Organic Solar Cell Application

Despite favorable absorption characteristics, borondipyrromethenes (BODIPYs) often lack thermal stability preventing their application in vacuum‐processed organic solar cells. In this paper, the replacement of the BF2 unit by borafluorene as a new functionalization strategy for this molecule class is explored. This approach is applied to a set of prototype molecules and demonstrates improved thermal stability, strong absorption in the red and near‐infrared region of the sun spectrum, as well as excellent solar cell performance. Synthesis is realized from free ligands via complexation with 9‐chloro‐9‐borafluorene giving high yields up to 81%. Planar heterojunction cells of these complexes exhibit high fill factors of more than 70%. Bulk heterojunction solar cells with C60 are optimized yielding power conversion efficiencies up to 4.5%, rendering the investigated prototype compounds highly competitive among other NIR‐absorbing small‐molecule donor materials. Comprehensive experimental material characterization and solar cell analysis are carried out, and the results are discussed together with simulations of molecular properties. Based on this analysis, additional performance improvements are proposed by engineering the intramolecular steric interactions towards further red‐shifted absorption.

Zero-dimensional (CH3NH3)3Bi2I9 perovskite for optoelectronic applications

We present the preparation and characterization of solution processed lead free films of zero-dimensional methylammonium iodo bismuthate (CH3NH3)3Bi2I9 perovskite. Structural characterization reveals the formation of hexagonal micro-crystals with preferred growth orientation along the c-axis. The material exhibits a wide band gap of 2.9eV and upon optical excitation the photoluminescence emission is observed at 1.65eV (751nm). Photoelectron spectroscopy confirms the stoichiometry of the (CH3NH3)3Bi2I9 perovskite and yields an ionization energy of 6.24eV, while Raman spectra confirm the vibrational modes of the bioctahedral inorganic anion framework (Bi2I9)3− in the low wavenumber regime (<200cm−1) regime. Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) are employed to evaluate the experimental results. We apply this novel bismuth-based hybrid perovskite in proof of principle simple heterojunction solar cell devices, which yield power conversion efficiencies of ~0.1%. Further enhancement is expected once the film morphology and device stack are optimized.

Quasi‐Solid‐State Dye‐Sensitized Solar Cells Based on Ru(II) Polypyridine Sensitizers

AbstractThe Ru(II) polypyridine complexes SA22 and SA25 consisting of anchoring and light harvesting moieties and possessing broad light absorption spectra were used to fabricate and optimize dye‐sensitized solar cells (DSSCs). The highly efficient Z960 electrolyte was used as redox‐mediator, and the J–V characteristics and incident photon‐to‐current conversion efficiency (IPCE) data were measured. The solar cells based on these dyes and electrolyte yielded power conversion efficiencies (PCE) of 7 % using SA22 and 5 % with SA25. The higher‐performance sensitizer SA22 was selected to build solar‐cell devices, using either the high‐thermal‐stability Z946 electrolyte or a gel‐electrolyte composed of Z946 electrolyte and 2 wt % low‐molecular‐mass organogelator (LMOG) NME‐5. The quasi‐solid‐state electrolyte produced a DSSC with a PCE of 4.7 %, whereas that made using Z946 showed 5 % efficiency. The quasi‐solid‐state DSSC was sealed and a stability study was performed using accelerated thermal aging conditions at 70 °C for 7 days, by which the cell parameters (including PCE, Jsc, Voc, and FF) retained more than 90 % of their original values.

Counter electrode electrocatalysts from one-dimensional coaxial alloy nanowires for efficient dye-sensitized solar cells

Pursuit of cost-effective counter electrode (CE) electrocatalysts with no sacrifice of photovoltaic performances has been a persistent objective for advanced dye-sensitized solar cell (DSSC) platforms. Here we demonstrate the experimental realization of CE electrocatalysts from Cu@M@Pt (M = Fe, Co, Ni) coaxial alloy nanowires for efficient DSSCs. The reasonable electrocatalytic activity is attributed to work function matching of alloy CEs to potential of I−/I3− and redistribute the electronic structure on the Pt surface. In comparison with 8.48% for the Pt nanotube CE based DSSC, the solar cells yield power conversion efficiencies up to 8.21%, 7.85%, and 7.30% using Cu@Fe@Pt, Cu@Co@Pt, and Cu@Ni@Pt NWs, respectively. This work represents an important step forward, as it demonstrates how to make the CE catalyst active and to accelerate the electron transport from CE to electrolyte for high-efficiency but cost-effective DSSC platforms.

Fabrication of polymer solar cells from organic nanoparticle dispersions by doctor blading or ink-jet printing

Dispersions of surfactant-free organic nanoparticles have proven a viable route to an eco-friendly lab-scale deposition of bulk-heterojunctions for polymer solar cells, matching the performance of solar cells deposited from toxic chlorinated solvents. In this work, we demonstrate the feasibility of doctor blading for the deposition of photo-active layers from organic nanoparticles comprising poly(3-hexylthiophene) and indene C60-bisadduct. The devices yielded power conversion efficiencies of 3.9% on 0.105 cm2 photo-active area and 3.4% on 1.1 cm2, being close to the performance of their spin cast counterparts. Likewise, the photo-active layers can be ink-jet printed yielding overall power conversion efficiencies of 2.9%, altogether rendering surfactant-free organic nanoparticles in eco-friendly dispersion agents a valuable process route to a sustainable large-area fabrication of organic solar cells.

A fast approach to optimize dye loading of photoanode via ultrasonic technique for highly efficient dye-sensitized solar cells

A distinctive method is proposed by simply utilizing ultrasonic technique in TiO2 electrode fabrication in order to improve the optoelectronic performance of dye-sensitized solar cells (DSSCs). Dye molecules are at random and single molecular state in the ultrasonic field and the ultrasonic wave favors the diffusion and adsorption processes of dye molecules. As a result, the introduction of ultrasonic technique at room temperature leads to faster and more well-distributed dye adsorption on TiO2 as well as higher cell efficiency than regular deposition, thus the fabrication time is markedly reduced. It is found that the device based on 40 kHz ultrasonic (within 1 h) with N719 exhibits a Voc of 789 mV, Jsc of 14.94 mA/cm2 and fill factor (FF) of 69.3, yielding power conversion efficiency (PCE) of 8.16%, which is higher than device regularly dyed for 12 h (PCE = 8.06%). In addition, the DSSC devices obtain the best efficiency (PCE = 8.68%) when the ultrasonic deposition time increases to 2.5 h. The DSSCs fabricated via ultrasonic technique presents more dye loading, larger photocurrent, less charge recombination and higher photovoltage. The charge extraction and electron impedance spectroscopy (EIS) were performed to understand the influence of ultrasonic technique on the electron recombination and performance of DSSCs.

Complementary split ring resonator arrays for electromagnetic energy harvesting

This work demonstrates the viability of Ground-backed Complementary Split-Ring Resonator (G-CSRR) arrays with significant power conversion efficiency and bandwidth enhancement in comparison to the technology used in current electromagnetic energy harvesting systems. Through numerical full-wave analysis, we demonstrated correlation between either the resonance frequency or the input impedance of G-CSRR cells with the periodicity of the array. A comparative study of power harvesting efficiency through numerical analysis and laboratory measurement was presented where an array of G-CSRRs is compared to an array of microstrip patch antennas. We demonstrated that a G-CSRR array yields power conversion efficiency of 92%, which represents a significant improvement in comparison to the single G-CSRR reported in our earlier work.

Charge transport model for photovoltaic devices based on printed polymer: Fullerene nanoparticles

The electrical transport properties of films derived from aqueous semiconducting nanoparticle are fully described by a phenomenological model that relates intrinsic film morphology to photovoltaic response. The model is applied to a new bulk heterojunction blend, composed of organic semiconducting nanoparticles formed from the polymer donor poly[{2,6-(4,8-didodecylbenzo[1,2-b:4,5-b']dithiophene)}-alt-{5,5-(2,5-bis(2-butyloctyl)-3,6-dithiophen-2-yl-2,5dihydropyrrolo[3,4-c]57pyrrole-1,4-dione)}] (P(TBT-DPP)) and the fullerene indene-C60-bisadduct (ICBA) synthesized by the miniemulsion method. The nanoparticle inks are printed from an aqueous dispersion onto flexible ITO-free substrates yielding power conversion efficiency of 2.6%.

Polymer Solar Cells with Efficiency &gt;10% Enabled via a Facile Solution‐Processed Al‐Doped ZnO Electron Transporting Layer

A facile and low‐temperature (125 °C) solution‐processed Al‐doped ZnO (AZO) buffer layer functioning very effectively as electron accepting/hole blocking layer for a wide range of polymer:fullerene bulk heterojunction systems, yielding power conversion efficiency in excess of 10% (8%) on glass (plastic) substrates is described. The ammonia‐treatment of the aqueous AZO nanoparticle solution produces compact, crystalline, and smooth thin films, which retain the aluminum doping, and eliminates/reduces the native defects by nitrogen incorporation, making them good electron transporters and energetically matched with the fullerene acceptor. It is demonstrated that highly efficient solar cells can be achieved without the need for additional surface chemical modifications of the buffer layer, which is a common requirement for many metal oxide buffer layers to yield efficient solar cells. Also highly efficient solar cells are achieved with thick AZO films (&gt;50 nm), highlighting the suitability of this material for roll‐to‐roll coating. Preliminary results on the applicability of AZO as electron injection layer in F8BT‐based polymer light emitting diode are also presented.

Thin Films of Dendritic Anatase Titania Nanowires Enable Effective Hole‐Blocking and Efficient Light‐Harvesting for High‐Performance Mesoscopic Perovskite Solar Cells

To achieve high‐performance perovskite solar cells, especially with mesoscopic cell structure, the design of the electron transport layer (ETL) is of paramount importance. Highly branched anatase TiO2 nanowires (ATNWs) with varied orientation are grown via a facile one‐step hydrothermal process on a transparent conducting oxide substrate. These films show good coverage with optimization obtained by controlling the hydrothermal reaction time. A homogeneous methyl­ammonium lead iodide (CH3NH3PbI3) perovskite thin film is deposited onto these ATNW films forming a bilayer architecture comprising of a CH3NH3PbI3 sensitized ATNW bottom layer and a CH3NH3PbI3 capping layer. The formation, grain size, and uniformity of the perovskite crystals strongly depend on the degree of surface coverage and the thickness of the ATNW film. Solar cells constructed using the optimized ATNW thin films (220 nm in thickness) yield power conversion efficiencies up to 14.2% with a short‐circuit photocurrent density of 20.32 mA cm−2, an open‐circuit photovoltage of 993 mV, and a fill factor of 0.70. The dendritic ETL and additional perovskite capping layer efficiently capture light and thus exhibit a superior light harvesting efficiency. The ATNW film is an effective hole‐blocking layer and efficient electron transport medium for excellent charge separation and collection within the cells.

Cadmium sulfide interface layer for improving the performance of titanium dioxide/poly (3-hexylthiophene) solar cells by extending the spectral response

This work focused on studying the effect of cadmium sulfide (CdS) interfacial layer on the performance of titanium dioxide (TiO2)/poly (3-hexylthiophene) (P3HT) solar cells and finding out its effect on charge recombination dynamics of hybrid TiO2/P3HT solar cells. FESEM images confirm the uniform distribution of chemical bath deposited CdS layer on TiO2 nanoparticles. Insertion of CdS layer at the nanocrystalline TiO2/P3HT interface broadens quantum efficiency spectrum of the solar cells with peak values over 80 and 40 % at the wavelengths of maximum absorption of CdS and P3HT respectively and hence enhances short-circuit current density (JSC) from 3.5 to 5.9 mAcm−2 under simulated illumination (70 mWcm−2) with an AM 1.5 filter. CdS layer further improves open circuit voltage (VOC) from 0.35 to 0.57 V, which is consistent with higher built-in voltage in CdS/P3HT than in TiO2/P3HT due to relatively lower laying conduction band edge of CdS. Photovoltaic transient measurements show that the carrier life-time in TiO2/CdS/P3HT solar cell is an order of magnitude longer than that in TiO2/P3HT solar cell. Optimized TiO2/P3HT solar cells with CdS interlayer yield power conversion efficiencies over 1.5 %, which is three times greater than that for similar solar cells without CdS layer.

Highly efficient polymer solar cells cast from non-halogenated xylene/anisaldehyde solution

Several high performance polymer:fullerene bulk-heterojunctions are deposited from non-halogenated xylene/anisaldehyde solution, yielding power conversion efficiencies up to 9.5%.

Highly efficient planar perovskite solar cells through band alignment engineering

Planar perovskite solar cells exhibit a conduction band misalignment of the perovskite with TiO2, but not with SnO2. The system using the latter yielded power conversion efficiencies over 18%.

Understanding the formation of PEDOT:PSS films by ink-jet printing for organic solar cell applications

PEDOT:PSS films were ink-jet printed and were integrated into organic solar cell devices. The devices using printed films yield power conversion efficiencies comparable to the devices using spin coated PEDOT:PSS films.

CdS/CdSe co-sensitized TiO2 nanowire-coated hollow Spheres exceeding 6% photovoltaic performance

The development of an effective anode material with hierarchical multi-dimensional architecture is conducive to further improve the cell performance of photovoltaic devices. Herein we introduce an intriguing three-dimensional (3D) hierarchically branched hollow sphere-nanowire hybrid TiO2 photoanode for promising CdS and CdSe quantum dots co-sensitized solar cells application. The demonstrated 3D hierarchically hybrid photoanode owns a considerably high specific surface area while maintaining roomy space and providing ample porosity for efficient electrolyte infiltration. Moreover, the outstanding light scattering ability of such multi-dimensional architecture leads to an enhancement of light utilization efficiency and thus significantly enhanced short-circuit photocurrent. The control over the pore size of TiO2 hollow spheres and the optimizations on the newly developed chemical bath deposited (CBD) cuprous sulfide (Cu2S)/FTO counter electrode eventually yields power conversion efficiency as high as 6.01% for CdS/CdSe based quantum dot-sensitized solar cells (QDSSCs).