Mesoscopic Solar Cells Research Articles

Tailoring the porosity of MOF-derived N-doped carbon electrocatalysts for highly efficient solar energy conversion

Pore sizes of MOF-derived N-doped carbons were tailored for mesoscopic solar cell applications.

Formation of Stable Tin Perovskites Co-crystallized with Three Halides for Carbon-Based Mesoscopic Lead-Free Perovskite Solar Cells.

We synthesized and characterized methylammonium (MA) mixed tri-halide tin perovskites (MASnIBr2-x Clx ) for carbon-based mesoscopic solar cells free of lead and hole-transporting layers. Varied SnCl2 /SnBr2 ratios yielded tin perovskites with three halides (I, Br, and Cl) co-crystallized inside the tin-perovskite. When the SnCl2 proportion was ≥50 % (x≥1), phase separation occurred to give MASnI3-y Bry and MASnCl3-z Brz in the stoichiometric proportions of their precursors, confirmed by XRD. A device with MASnIBr1.8 Cl0.2 (SnCl2 =10 %) showed the best photovoltaic performance: JSC =14.0 mA cm-2 , VOC =380 mV, FF=0.573, and PCE=3.1 %, and long-term stability. Electrochemical impedance spectra (EIS) show superior charge recombination and dielectric relaxation properties for the MASnIBr1.8 Cl0.2 cell. Transient PL decays showed the intrinsic problem of tin-based perovskites with average lifetimes less than 100 ps.

Formation of Stable Tin Perovskites Co‐crystallized with Three Halides for Carbon‐Based Mesoscopic Lead‐Free Perovskite Solar Cells

AbstractWe synthesized and characterized methylammonium (MA) mixed tri‐halide tin perovskites (MASnIBr2−xClx) for carbon‐based mesoscopic solar cells free of lead and hole‐transporting layers. Varied SnCl2/SnBr2 ratios yielded tin perovskites with three halides (I, Br, and Cl) co‐crystallized inside the tin‐perovskite. When the SnCl2 proportion was ≥50 % (x≥1), phase separation occurred to give MASnI3−yBry and MASnCl3−zBrz in the stoichiometric proportions of their precursors, confirmed by XRD. A device with MASnIBr1.8Cl0.2 (SnCl2=10 %) showed the best photovoltaic performance: JSC=14.0 mA cm−2, VOC=380 mV, FF=0.573, and PCE=3.1 %, and long‐term stability. Electrochemical impedance spectra (EIS) show superior charge recombination and dielectric relaxation properties for the MASnIBr1.8Cl0.2 cell. Transient PL decays showed the intrinsic problem of tin‐based perovskites with average lifetimes less than 100 ps.

Hexagonal Array of Mesoscopic HTM‐Based Perovskite Solar Cell with Embedded Plasmonic Nanoparticles

Inorganic hole‐transporting materials (HTMs) profoundly improve the stability and robustness of the solar cell compared to that expected from organic HTMs. In this work, the efficiency of a perovskite solar cell is greatly enhanced using a hexagonal nanoprism array of inorganic metal oxide HTM. We found that the introduced structure increases the efficiency of the mesoscopic configuration by 42% higher than that of the planar perovskite solar cell with the same thickness of the active layers. The reason of this enhancement in power conversion efficiency is the better carrier transportation in the mesoscopic configuration. The periodic array of mesoscopic hole‐transporting layer is vastly tunable and reveals unique capabilities of designing a particular array, which can enhance the efficiency of the perovskite solar cell. We also incorporated plasmonic nanoparticles into the absorber layer and found that they significantly could improve the performance of the solar cell. The inclusion of spherical nanoparticles improves the light absorption of the bare mesoscopic solar cell. An increasing number of nanoparticles enhances the light trapping inside the active layer and as a result improves the probability of light absorption.

Multidimensional Anodized Titanium Foam Photoelectrode for Efficient Utilization of Photons in Mesoscopic Solar Cells.

Mesoscopic solar cells based on nanostructured oxide semiconductors are considered as a promising candidates to replace conventional photovoltaics employing costly materials. However, their overall performances are below the sufficient level required for practical usages. Herein, this study proposes an anodized Ti foam (ATF) with multidimensional and hierarchical architecture as a highly efficient photoelectrode for the generation of a large photocurrent. ATF photoelectrodes prepared by electrochemical anodization of freeze-cast Ti foams have three favorable characteristics: (i) large surface area for enhanced light harvesting, (ii) 1D semiconductor structure for facilitated charge collection, and (iii) 3D highly conductive metallic current collector that enables exclusion of transparent conducting oxide substrate. Based on these advantages, when ATF is utilized in dye-sensitized solar cells, short-circuit photocurrent density up to 22.0 mA cm-2 is achieved in the conventional N719 dye-I3- /I- redox electrolyte system even with an intrinsically inferior quasi-solid electrolyte.

Organic-Inorganic Copper(II)-Based Material: A Low-Toxic, Highly Stable Light Absorber for Photovoltaic Application.

Lead halide perovskite solar cells have recently emerged as a very promising photovoltaic technology due to their excellent power conversion efficiencies; however, the toxicity of lead and the poor stability of perovskite materials remain two main challenges that need to be addressed. Here, for the first time, we report a lead-free, highly stable C6H4NH2CuBr2I compound. The C6H4NH2CuBr2I films exhibit extraordinary hydrophobic behavior with a contact angle of ∼90°, and their X-ray diffraction patterns remain unchanged even after 4 h of water immersion. UV/vis absorption spectrum shows that C6H4NH2CuBr2I compound has an excellent optical absorption over the entire visible spectrum. We applied this copper-based light absorber in printable mesoscopic solar cell for the initial trial and achieved a power conversion efficiency of ∼0.5%. Our study represents an alternative pathway to develop low-toxic and highly stable organic-inorganic hybrid materials for photovoltaic application.

Synergy of ammonium chloride and moisture on perovskite crystallization for efficient printable mesoscopic solar cells

Organometal lead halide perovskites have been widely used as the light harvester for high-performance solar cells. However, typical perovskites of methylammonium lead halides (CH3NH3PbX3, X=Cl, Br, I) are usually sensitive to moisture in ambient air, and thus require an inert atmosphere to process. Here we demonstrate a moisture-induced transformation of perovskite crystals in a triple-layer scaffold of TiO2/ZrO2/Carbon to fabricate printable mesoscopic solar cells. An additive of ammonium chloride (NH4Cl) is employed to assist the crystallization of perovskite, wherein the formation and transition of intermediate CH3NH3X·NH4PbX3(H2O)2 (X=I or Cl) enables high-quality perovskite CH3NH3PbI3 crystals with preferential growth orientation. Correspondingly, the intrinsic perovskite devices based on CH3NH3PbI3 achieve an efficiency of 15.6% and a lifetime of over 130 days in ambient condition with 30% relative humidity. This ambient-processed printable perovskite solar cell provides a promising prospect for mass production, and will promote the development of perovskite-based photovoltaics.

Lead-free pseudo-three-dimensional organic–inorganic iodobismuthates for photovoltaic applications

X-ray diffraction, electronic characterisation and mesoscopic solar cell evaluation were performed for two novel iodobismuthates, C5H6NBiI4([py][BiI4]) and C6H8NBiI4([mepy][BiI4]).

Role of Tin Chloride in Tin-Rich Mixed-Halide Perovskites Applied as Mesoscopic Solar Cells with a Carbon Counter Electrode

We report the synthesis and characterization of alloyed Sn–Pb methylammonium mixed-halide perovskites (CH3NH3SnyPb1–yI3–xClx) to extend light harvesting toward the near-infrared region for carbon-based mesoscopic solar cells free of organic hole-transport layers. The proportions of Sn in perovskites are well-controlled by mixing tin chloride (SnCl2) and lead iodide (PbI2) in varied stoichiometric ratios (y = 0–1). SnCl2 plays a key role in modifying the lattice structure of the perovskite, showing anomalous optical and optoelectronic properties; upon increasing the concentration of SnCl2, the variation of the band gap and band energy differed from those of the SnI2 precursor. The CH3NH3SnyPb1–yI3–xClx devices showed enhanced photovoltaic performance upon increasing the proportion of SnCl2 until y = 0.75, consistent with the corresponding potential energy levels. The photovoltaic performance was further improved upon adding 30 mol % tin fluoride (SnF2) with device configuration FTO/TiO2/Al2O3/NiO/C, produc...

Light Harvesting: Enhanced Light Harvesting in Mesoscopic Solar Cells by Multilevel Multiscale Patterned Photoelectrodes with Superpositioned Optical Properties (Adv. Funct. Mater. 36/2016)

Light Harvesting: Enhanced Light Harvesting in Mesoscopic Solar Cells by Multilevel Multiscale Patterned Photoelectrodes with Superpositioned Optical Properties (Adv. Funct. Mater. 36/2016)

Direct Observation of Ferroelectricity and Charge Separation Process in CH3NH3PbI3 Perovskite Solar Cell

In recent years, organometallic trihalide perovskites has attracted more and more attention for the application of solar cells. In particular, methylammonium (MA) lead triiodide (CH3NH3PbI3 or MAPbI3) has attracted the most attention and undergoes rapid development since it was first applied as light absorber in mesoscopic solar cells. Up to now, it has been demonstrated that the power conversion efficiency of MAPbI3 based solar cells can reach 20%, which is directly related to the favorable direct band gap, high carrier mobilities and long carrier diffusion length. To further improve the performance of MAPbI3 based solar cell, researchers have been focused on studying the otpical, electronic, and optoelectronic properties of MAPbI3 perovskites extensively. However, there is not a systematic study of its ferroelectric properties and the correlation between its ferroelectricity and its optoelectronic properties. Here, we report our direct observation of the ferroelectric domain structure in MAPbI3 thin film using piezoresponse force microscope (PFM). A strong evidence of the intrinsic ferroelectricity is that the ferroelectric domain structure has no correlation to its crystal domain structure, as shown in figure 1. Besides, we also observed the characteristic butterfly loop and hysteresis loop from pointwise experiment, to further verify the ferroelectricity. In addition to using PFM, we also directly observed the charge separation process by measuring the surface potential with Kelvin probe force microscope (KPFM). Under laser illumination when the charge carriers are generated, the surface potential will either decrease or increase depending on the device structure (p-i-n or n-i-p), which can be probed with KPFM and correlated with the surface topography as well. Our preliminary study shows that with AFM’s capability of localized probing, both the ferroelectric property and the optoelectronic properties can be measured and correlated to the structure, which can help us better understand the role of ferroelectricity in the high performance of organometallic trihalide perovskites. Figure 1

N-type metal-oxide electron transport layer for mesoscopic perovskite solar cells

To meet the challenge of continuously increasing global energy demands, organic-inorganic halide based perovskite solar cells (PSCs) have garnered great attention from the photovoltaic research community for their low cost and high efficiency. The efficiency of perovskite-based mesoscopic solar cells increases rapidly, from 3.8% in 2009 to 22.1% in 2016. N-type metal-oxide electron transport layer, as one of the important components in mesoscopic PSCs (MPSCs), acts as not only a scaffold layer for the growth of perovskite crystals, but also a layer to supply transfer pathways for electrons injected from perovskites. In this review, we discussed recent published reports of MPSCs with the focus on n-type metal-oxide electron transport layer in MPSCs. The scaffold materials, scaffold nanostructure, and scaffold/perovskite interface engineering are considered, and the effects of these modifications of scaffolds on the performance of MPSCs are summarized in this review.

Impact of a Mesoporous Titania-Perovskite Interface on the Performance of Hybrid Organic-Inorganic Perovskite Solar Cells.

We report on the optimization of the interfacial properties of titania in mesoscopic CH3NH3PbI3 solar cells. Modification of the mesoporous TiO2 film by TiCl4 treatment substantially reduced the surface traps, as is evident from the sharpness of the absorption edge with a significant reduction in Urbach energy (from 320 to 140 meV) determined from photothermal deflection spectroscopy, and led to an order of magnitude enhancement in the bulk electron mobility and corresponding decrease in the transport activation energy (from 170 to 90 meV) within a device. After optimization of the photoanode-perovskite interface using various sizes of TiO2 nanoparticles, the best photovoltaic efficiency of 16.3% was achieved with the mesoporous TiO2 composed of 36 nm sized nanoparticles. The improvement in device performance can be attributed to the enhanced charge collection efficiency that is driven by improved charge transport in the mesoporous TiO2 layer. Also, the decreased recombination at the TiO2-perovskite interface and better perovskite coverage play important roles.

Two-step ultrasonic spray deposition of CH3NH3PbI3 for efficient and large-area perovskite solar cell

A two-step ultrasonic spray method has been developed to fabricate centimeter-scale uniform and smooth perovskite CH3NH3PbI3 films for efficient and large-area solar cells. Aside from the advantages in larger area and higher smoothness, the perovskite films deposited by this method showed better crystallinity, lower non-radiative recombination and more efficient interfacial charge extraction properties. Through systematical optimizations, an efficient mesoscopic solar cell was finally achieved with efficiency of 16.03%. Furthermore, large-area (1×1cm2) cell was also fabricated, giving an efficiency of 13.09%. This work demonstrates that the two-step spray method can be a promising alternative to deposit high-quality and large-area perovskite absorbers to afford high cell performance.

Enhanced Light Harvesting in Mesoscopic Solar Cells by Multilevel Multiscale Patterned Photoelectrodes with Superpositioned Optical Properties

Investigations on nano‐ and micropatterns have been intensively performed in optical applications due to their light modulation effects for enhanced photon utilization. Recently, incorporation of periodic architectures in solar cells have brought significant enhancements in light harvesting and energy conversion efficiency, however, further improvements in performance are required for practical applications due to the intrinsic limitations of single‐level patterns. Herein, this study reports mesoscopic solar cells employing photoelectrodes with multilevel multiscale patterns. Polydimethylsiloxane film with multilevel nano/micropatterns (integrated in z‐axis direction) is prepared by LEGO‐like multiplex lithography, and its architecture is imprinted on mesoporous TiO2 electrode by soft molding technique. By various spectral analyses and simulations, advanced light harvesting properties by superposition of optical responses from constituent nano‐ and micropatterns are verified. The effectiveness of the strategy is confirmed by applications in dye‐sensitized solar cells as a model system, wherein over 17.5% increase in efficiency (by multilevel 400 nm line/20 μm dot structures) is observed. Also, external quantum efficiencies clearly exhibit that the improved light harvesting originates from the combined effects of diffraction grating and random scattering induced by both nano‐ and microarchitectures, respectively. Moreover, the validity of the multiscale approach in different dimensions is also confirmed in order to demonstrate the general advantages.

High Absorption Coefficient Cyclopentadithiophene Donor-Free Dyes for Liquid and Solid-State Dye-Sensitized Solar Cells

We report a series of “donor-free” dyes featuring moieties of oligo(4,4-dihexyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophene) (CPDT) functionalized with cyanoacrylic end groups for mesoscopic titania solar cells based on I–/I3– or Co(II)/Co(III) redox couple and spiro-OMeTAD hole transporter. These were compared with similar cells using an oligo(3-hexylthiophene) dye (5T), which we reported before. Extending the CPDT moiety of the dye molecules from one to three (denoted as CPDT-1, CPDT-2, and CPDT-3) widens the photoresponse overlap with the solar spectrum, increases the molar absorption coefficient up to 75 000 M–1 cm–1, and improves the short-circuit current (JSC), open-circuit voltage (VOC), and power conversion efficiency (PCE) for all types of DSSCs. Among these sensitizers, CPDT-3 shows the highest PCE of 6.7%, 7.3%, and 3.9% with I–/I3–, Co(II)/Co(III) redox couple, and spiro-OMeTAD hole transporter, respectively, compared with 7.6%, 9.0%, and 4.0% for 5T. Benefiting from the high absorption of CPDT-3, ...

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.

Tin chloride perovskite-sensitized core/shell photoanode solar cell with spiro-MeOTAD hole transport material for enhanced solar light harvesting

An attempt has been made to fabricate methyl ammonium tin chloride (CH3NH3SnCl3) perovskite-sensitized TiO2 nanostructure photoanode solar cell with hole transport material (HTM) spiro-MeOTAD and graphite-coated counter electrode (CE). The TiO2 nanoparticles (TNPs), TiO2 nanoleaves (TNLs), and TNLs with MgO core/shell photoanodes were prepared to fabricate perovskite-sensitized solar cells (PSSCs). The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photovoltaic characteristics of the PSSCs, photocurrent density (J sc), open-circuit voltage (V oc), fill factor (FF), and power conversion efficiency (PCE) were determined under illumination of AM 1.5 G. Electrochemical impedance spectroscopy (EIS) analysis was carried out to study the charge transport and lifetime of charge carriers at the photoanode–sensitizer–electrolyte interface of the PSSCs. The PSSC made with CH3NH3SnCl3 perovskite-sensitized TNL–MgO core/shell photoanode and spiro-MeOTAD HTM shows an impressive photovoltaic performance, with J sc = 17.24 mA/cm2, V oc = 800 mV, FF = 73 %, and PCE = 9.98 % under 100 mW/cm2 light intensity. The advent of such simple solution-processed mesoscopic heterojunction solar cells paves the way to realize low-cost and high-efficiency solar cells. By the aid of electrochemical impedance spectroscopy, it is revealed that the core/shell structure can increase an interfacial resistance of the photoanode–CH3NH3SnCl3 interface and retard an electron recombination process in the photoanode–sensitizer–HTM interface.

(Invited) Infra-Red Photoresponse of Mesoscopic NiO-Based Solar Cells Sensitized with PbS Quantum Dot

Sensitization of mesoscopic NiO films with molecular dyes has attracted a growing scientific interest because these photocathodes represent the key component of tandem dye-sensitized solar cells and tandem dye-sensitized photoelectrosynthetic cells. In this area, quantum dots (QDs) were much less investigated than molecular sensitizers although they proved to be particularly promising light collectors in other photovoltaic technologies such as Schottky type solar cells and conventional TiO2 based n-QDSSCs. In this presentation, we demonstrate that PbS QDs are promising inorganic sensitizers for NiO based p-DSSCs. Photocurrent is produced until far in the IR (above 950 nm) with a cobalt complex as redox couple supportting thus the real potential of quantum dot sensitized NiO-based photocathodes to exploit the low energy part of the solar spectrum.

Infra-red photoresponse of mesoscopic NiO-based solar cells sensitized with PbS quantum dot.

Sensitized NiO based photocathode is a new field of investigation with increasing scientific interest in relation with the development of tandem dye-sensitized solar cells (photovoltaic) and dye-sensitized photoelectrosynthetic cells (solar fuel). We demonstrate herein that PbS quantum dots (QDs) represent promising inorganic sensitizers for NiO-based quantum dot-sensitized solar cells (QDSSCs). The solar cell sensitized with PbS quantum dot exhibits significantly higher photoconversion efficiency than solar cells sensitized with a classical and efficient molecular sensitizer (P1 dye = 4-(Bis-{4-[5-(2,2-dicyano-vinyl)-thiophene-2-yl]-phenyl}-amino)-benzoic acid). Furthermore, the system features an IPCE (Incident Photon-to-Current Efficiency) spectrum that spreads into the infra-red region, reaching operating wavelengths of 950 nm. The QDSSC photoelectrochemical device works with the complexes tris(4,4′-ditert-butyl-2,2′-bipyridine)cobalt(III/II) redox mediators, underscoring the formation of a long-lived charge-separated state. The electrochemical impedance spectrocopy measurements are consistent with a high packing of the QDs upon the NiO surface, the high density of which limits the access of the electrolyte and results in favorable light absorption cross-sections and a significant hole lifetime. These notable results highlight the potential of NiO-based photocathodes sensitized with quantum dots for accessing and exploiting the low-energy part of the solar spectrum in photovoltaic and photocatalysis applications.