Near-infrared Light Harvesting Research Articles

Photothermal Welding Strategy for Mechanical Stability and High Efficiency of ETL‐Free f‐PSCs

AbstractFlexible perovskite solar cells (f‐PSCs) have drawn widespread interest owing to their distinguished advantages in excellent flexibility and relatively low cost. However, the brittle grain boundaries (GBs) and defects in flexible perovskite film tremendously influence the power conversion efficiency (PCE) and mechanical flexibility of f‐PSCs. Herein, photothermal welding, a novel method, is used to improve the perovskite films quality and the PCE of f‐PSCs with a near‐infrared (NIR) dye (indocyanine green, ICG) and polycaprolactone (PCL) as additives. Due to the strong photothermal effect, ICG molecule not only can significantly enhance NIR light harvesting, but it also can weld GBs upon exposure to an NIR laser, which is conducive to the GBs connections and device flexibility. Meanwhile, the S═O bond of ICG and C═O bond of PCL can simultaneously coordinate with Pb2+ defects in perovskite. Furthermore, they can control crystal growth to form a smooth surface of perovskite film. Consequently, the unencapsulated PSCs based on ICG/PCL displays a high champion PCE of 20.62%, with 88.4% of the original PCE after being placed in dark conditions for 600 h. The f‐PSCs delivers a champion PCE of 19.55% and exhibits excellent mechanical stability, thus providing a meaningful scientific direction to fabricate high‐flexible f‐PSCs.

NIR-responsive carbon dots as an oxidative-stress amplifier and hyperthermia-induced superior photothermal in-vitro anticancer activity

A facile wet chemistry-based strategy was developed to synthesize orange emissive Carbon dots (O-CDs) based on dehydration-induced ring-fusion of the precursor (1,3-dihydroxynaphthalene) in a dehydrating sulfuric acid medium. The O-CDs revealed significant Near-infrared (808 nm) light harvesting potential with outstanding photothermal conversion efficiency (∼58%) and hence exhibited excellent NIR-light stimulated photothermal anticancer performance. Furthermore, these fluorescent O-CD nanoprobes displayed excitation-dependent polychromatic emissions in the range of 540–640 nm, with the dual emission maxima at 540 and 580 nm, corresponding to yellow and orange emission at the excitation of 490 nm. Various mitochondrial, as well as cytoplasmic apoptosis-related proteins and genes were upregulated during photothermal treatment, which suggests that hyperthermia and oxidative stress have a major impact on cell death. The anticancer activity of O-CDs is likely due to the elevated reactive oxygen species (ROS) amplification in cooperation with the hyperthermia effect. This study offers a potential alternative to bio-nanomedicine for cancer treatment by carbon-based photothermal therapy.

Dual-rotor strategy for organic cocrystals with enhanced near-infrared photothermal conversion.

Organic cocrystal engineering provides a promising route to promote the near-infrared (NIR) light harvesting and photothermal conversion (PTC) abilities of small organic molecules through the rich noncovalent bond interactions of D/A units. Besides, the single-bond rotatable groups known as "rotors" are considered to be conducive to the nonradiative transitions of the excited states of organic molecules. Herein, we propose a single-/double-bond dual-rotor strategy to construct D-A cocrystals for NIR PTC application. The results reveal that the cocrystal exhibits an ultra-broadband absorption from 300 nm to 2000 nm profiting from the strong π-π stacking and charge transfer interactions, and the weakened p-π interaction. More importantly, the PTC efficiency of cocrystals at 1064 nm in the NIR-II region can be largely enhanced by modulating the number of rotor groups and the F-substituents of D/A units. As is revealed by fs-TA spectroscopy, the superior NIR PTC performance can be attributed to the nonradiative decays of excited states induced by the free rotation of the single-bond rotor (-CH3) from the donors and the inactive double-bond rotor ([double bond, length as m-dash]C(C[triple bond, length as m-dash]N)2) being in the active form of [-C(C[triple bond, length as m-dash]N)2] in the excited states from the acceptors. This prototype displays a promising route to extend the functionalization of small organic molecules based on organic cocrystal engineering.

Construction of Core-shell Sb2 s3 @Cds Nanorod with Enhanced Heterointerface Interaction for Chromium-Containing Wastewater Treatment.

How to collaboratively reduce Cr(VI) and break Cr(III) complexes is a technical challenge to solve chromium-containing wastewater (CCW) pollution. Solar photovoltaic (SPV) technology based on semiconductor materials is a potential strategy to solve this issue. Sb2 S3 is a typical semiconductor material with total visible-light harvesting capacity, but its large-sized structure highly aggravates disordered photoexciton migration, accelerating the recombination kinetics and resulting low-efficient photon utilization. Herein, the uniform mesoporous CdS shell is in situ formed on the surface of Sb2 S3 nanorods (NRs) to construct the core-shell Sb2 S3 @CdS heterojunction with high BET surface area and excellent near-infrared light harvesting capacity via a surface cationic displacement strategy, and density functional theory thermodynamically explains the breaking of SbS bonds and formation of CdS bonds according to the bond energy calculation. The SbSCd bonding interaction and van der Waals force significantly enhance the stability and synergy of Sb2 S3 /CdS heterointerface throughout the entire surface of Sb2 S3 NRs, promoting the Sb2 S3 -to-CdS electron transfer due to the formation of built-in electric field. Therefore, the optimized Sb2 S3 @CdS catalyst achieves highly enhanced simulated sunlight-driven Cr(VI) reduction (0.154 min-1 ) and decomplexation of complexed Cr(III) in weakly acidic condition, resulting effective CCW treatment under co-action of photoexcited electrons and active radicals. This study provides a high-performance heterostructured catalyst for effective CCW treatment by SPV technology.

Near-infrared light harvesting of upconverting Y2O3:Er3+ nanoparticles and their photovoltaic application

Light harvesting plays a significant role in the enhancement on photovoltaic performance. It is closely associated with the photocurrent of solar cells. It is possible to improve light harvesting by material substitution as well as expansion of absorptive edge. Therefore, upconversion characteristics is one of promising solutions for better light harvesting. Upconverting materials emit visible light which is available for photoconversion after they absorb invisible near-infrared (NIR) light. In this study, Er3+ doped Y2O3 (Y2O3:Er3+) nanoparticles were used as upconverting material. Its strong emissions of green and red light corresponding to 2H11/2 and 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions were clearly demonstrated under NIR irradiation of 975 nm wavelength. These emissions were apparently absorbed by dye-sensitized electrode. Based on these results, Y2O3:Er3+ nanoparticles were introduced into dye-sensitized solar cells (DSCs). After incorporating Y2O3:Er3+ nanoparticles, photovoltage was increased due to its high band-gap energy of about 5 eV. On the other hand, the photocurrent was decreased because of the decrease in adsorbed dye amount and electron paths. However, the photoconversion edge was obviously expanded. As a result, DSC performance was enhanced with optimum upconverting particles. It exhibited an efficiency of 8.03%, which was higher than that of a conventional DSC.

Ultrafast Intermolecular Interaction Dynamics between NIR-Absorbing Unsymmetrical Squaraines and PCBM: Effects of Halogen Substitution.

Among near-infrared (NIR) dyes, squaraine derivatives are applied as efficient sensitizers in optoelectronic and biomedical devices due to their simple synthesis, intense absorption, and emission and exceptional photochemical stability. The fundamental understanding of the structure-property relationships of sensitizers provides the insight to increase the efficiency of such devices. Here, unsymmetrical squaraine derivatives (ABSQs) with donor-acceptor-donor (D-A-D') architectures having N,N-dimethyl amino anthracene and benzothiazole (ABSQ-H) halogenated with fluoride (ABSQ-F), chloride (ABSQ-Cl), and bromide (ABSQ-Br) were synthesized to understand the effect of halogen on the photophysical properties and intermolecular interaction dynamics with phenyl-C61-butyric acid methyl ester (PCBM), which is used widely as an electron acceptor in bulk heterojunction-based devices. Interestingly, ABSQ-H exhibited intense absorption (ε ∼ 6.72 × 104 M-1 cm-1) spectra centered at ∼660 nm. Upon halogen substitution, a bathochromic shift in the absorption spectra with an increase of molar absorptivity was observed (ε ∼ 8.59 × 104 M-1 cm-1), which is beneficial for NIR light harvesting. The femtosecond transient absorption spectra of ABSQs revealed that the polarity of the solvent controlled the excited-state relaxation dynamics. Upon addition of PCBM, the fluorescence intensity and dynamics of halogenated ABSQs were quenched, and the formation of a squaraine radical cation was observed, reflecting the occurrence of intermolecular charge-transfer dynamics between ABSQs and PCBM. Thus, the observation of a bathochromic shift with intense absorption and an efficient intermolecular interaction with PCBM upon halogenation of ABSQs provide a design strategy for the development of unsymmetrical squaraine derivatives for bulk heterojunction-based optoelectronic devices.

Suppressing interface charge recombination for efficient integrated perovskite/organic bulk-heterojunction solar cells

Integrated perovskite/bulk-heterojunction (BHJ) solar cells offer a novel way to achieve high-performance photovoltaics exceeding Shockley-Queisser limit through the utilization of complementary light absorption spectra. Despite improved photocurrent benefited from the additional near-infrared light harvesting, undesirable decrease of open-circuit voltage and fill factor are often observed due to severe charge recombination at the perovskite/BHJ interface. Herein, ultrathin bathocuproine (BCP) and zirconium acetylacetonate (ZrAcac) are inserted between perovskite and BHJ as interface modification to regulate carrier extraction and inhibit charge recombination at the interface. Fermi energy levels of perovskite shift upward after BCP and ZrAcac modification, indicating higher built-in electric field at the perovskite/BHJ interface, which is supported by the capacitance-voltage measurements. Enhanced carrier extraction and suppressed charge recombination are confirmed at the perovskite/BHJ interface according to the photoluminescence spectra and semiconductor device measurement. Consequently, large improvements of Voc and FF are obtained without sacrificing the photocurrent, resulting in a champion conversion efficiency, which is among the highest reported efficiencies of integrated perovskite/BHJ solar cells so far. Our work provides a feasible exploration from the perspective of interface modification for achieving high-efficiency integrated perovskite/BHJ photovoltaics.

Toward Broad Spectral Response Inverted Perovskite Solar Cells: Insulating Quantum‐Cutting Perovskite Nanophosphors and Multifunctional Ternary Organic Bulk‐Heterojunction

AbstractExtending near‐infrared (NIR) spectral response and increasing ultraviolet utilization is still a challenge in the context of improving power conversion efficiency (PCE) for perovskite solar cells (PSCs). In this work, to extend NIR light‐harvesting of PSCs, a novel COTIC‐4F: PC61BM: PTB7‐Th ternary organic bulk‐heterojunction together with Au nanotriangles is integrated on the PSCs. The NIR spectral response is thus extended to 1100 nm. In fact, the COTIC‐4F: PC61BM: PTB7‐Th layer enables multi‐functional effects, which can serve as electron transport, trap passivation, and moisture barrier layer in addition to NIR light harvesting. For increasing UV utilization, CsPbCl3:Yb3+, Ce3+, Cr3+ nanophosphors with photoluminescent quantum yield close to 200% are fabricated, which demonstrate excellent down‐conversion ability. Then, CsPbCl3: Yb3+, Ce3+, Cr3+/polymethylmethacrylate composite films are self‐assembled on a hybrid device, resulting in a 6.2% relative enhancement of short circuit current density. After simultaneously improving the NIR and UV spectral response of device, the PCE is increased significantly from 20.52% to 23.40% and the Jsc is increased from 21.79 to 25.96 mA cm−2, representing one of the highest PCE and maximum Jsc enhancements in the reported inverted hybrid organic/PSCs. This work represents an effective and general strategy for obtaining efficient and stable PSC devices with extremely broad spectral responses.

Dual interfacial engineering to improve ultraviolet and near-infrared light harvesting for efficient and stable perovskite solar cells

The light loss caused by the incomplete utilization of the solar energy spectrum is a key factor that impedes the photoelectric conversion efficiency of perovskite solar cells (PSCs). Hence, reducing the light escape through enhancing the utilization of ultraviolet (UV) light, and expanding the response of PSCs in the near-infrared (NIR) range is the key factor to further improve the photoelectric conversion efficiency (PCE) of PSCs. However, there is a lack of literature on engineering UV and NIR light harvesting at the same time. Herein, the NaYF4:Ce,Tb@NaYF4 core–shell nanocrystals with efficient photon downconversion ability from UV to visible are designed to be embedded in the electron transporting layer (ETL), which serves as the photon downconverters and defect passivators, successfully improving the light response in both UV and visible region. The CIGSe quantum dots (QDs) with excellent infrared light harvesting ability, together with the plasmonic Au nanorods (NRs), are assembled in the hole transporting layer (HTL) to expand and improve the NIR light harvesting. The light response of the PSCs was successfully broadened to the NIR region from 800 to 920 nm. As a result, the champion PSC device insulating with NaYF4:Ce,Tb@NaYF4 nanocrystals and CIGSe QDs demonstrates a remarkably increased PCE from 19.38% to 22.60%. The modified PSC devices also demonstrate highly improved UV and long-term stability. This work suggests a universal strategy to improve the UV and near-infrared light harvesting of PSCs, which is of great importance for fabricating PSCs with response to full spectrum.

Recent Advances in the Design and Photocatalytic Enhanced Performance of Gold Plasmonic Nanostructures Decorated with Non-Titania Based Semiconductor Hetero-Nanoarchitectures

Plasmonic photocatalysts combining metallic nanoparticles and semiconductors have been aimed as versatile alternatives to drive light-assisted catalytic chemical reactions beyond the ultraviolet (UV) regions, and overcome one of the major drawbacks of the most exploited photocatalysts (TiO2 or ZnO). The strong size and morphology dependence of metallic nanostructures to tune their visible to near-infrared (vis-NIR) light harvesting capabilities has been combined with the design of a wide variety of architectures for the semiconductor supports to promote the selective activity of specific crystallographic facets. The search for efficient heterojunctions has been subjected to numerous studies, especially those involving gold nanostructures and titania semiconductors. In the present review, we paid special attention to the most recent advances in the design of gold-semiconductor hetero-nanostructures including emerging metal oxides such as cerium oxide or copper oxide (CeO2 or Cu2O) or metal chalcogenides such as copper sulfide or cadmium sulfides (CuS or CdS). These alternative hybrid materials were thoroughly built in past years to target research fields of strong impact, such as solar energy conversion, water splitting, environmental chemistry, or nanomedicine. Herein, we evaluate the influence of tuning the morphologies of the plasmonic gold nanostructures or the semiconductor interacting structures, and how these variations in geometry, either individual or combined, have a significant influence on the final photocatalytic performance.

Oxygen-doped crystalline carbon nitride with greatly extended visible-light-responsive range for photocatalytic H2 generation

Crystalline carbon nitride (CCN) materials with photoresponse of more than 600 nm are rare. Here, we successfully prepared a series of oxygen doped K+ implanted CCN (KCN) with narrowed bandgap (2.71−1.62 eV) for the first time. Compared with most of the O-doped amorphous CN, the optical absorption can only reach 500 nm, and a few more than 500 nm, our oxygen doping strategy is adopted to activate more n→π* transitions to enhance visible light and even near-infrared light harvesting. This active-optimized O-doped KCN accounts for 45- and 10- times promotion than pristine CN and KCN in H2 generation under λ > 500 nm. Most importantly, its maximum active wavelength is up to 650 nm, which has obvious advantages than most CCN-based photocatalysts in the utilization of solar energy. This excellent solar capture and H2 production is attributed to the activated n→π* electron transition, and high crystallinity and conduction band (CB) position caused by oxygen doping.

High-Performance Semitransparent Organic Photovoltaics Featuring a Surface Phase-Matched Transmission-Enhancing Ag/ITO Electrode.

In this study, we designed a surface phase-matched transmission enhancement top electrode-Ag/indium tin oxide (ITO) structure for highly efficient and aesthetic semitransparent organic photovoltaics (ST-OPVs). The purposed highly transparent back electrodes (Ag/ITO) could selectively decrease visible reflection and increase transparency accordingly. By altering the thicknesses of the Ag and ITO layers, we could control the transmittance curve and increase the transparency of the ST-OPV devices. Devices based on PTB7-Th:IEICO-4F and PM6:Y6:PC71BM displayed outstanding performance (8.1 and 10.2%, respectively) with high photopic-weighted visible light transmittance (36.2 and 28.6%, respectively). The outstanding visible and near-infrared light harvesting of PM6:Y6:PC71BM further allowed a new application: double-sided energy harvesting from solar and indoor illumination. The simple optical design of a top electrode displaying high transparency/conductivity has a wide range of potential applications in, for example, greenhouse photovoltaics, tandem cells, and portable devices.

Silicon nitride grating based planar spectral splitting concentrator for NIR light harvesting.

We design a multi-layered solar spectral splitting planar concentrator for near infrared (NIR) light energy harvesting application. Each layer includes a silicon nitride based subwavelength diffraction grating on top of a glass substrate that is optimized to diffract the incoming solar radiation in a specific band from a broad spectral band (700-1400 nm in the NIR region) into guided modes propagating inside the glass substrate. The steep diffraction angle due to subwavelength grating results in concentrated light at the edge of each layer where it is then converted to electricity using a photovoltaic cell. The spectral splitting planar concentrator shows an overall NIR guiding efficiency of ∼18%, and power conversion efficiency of ∼11%. The design can be potentially used for building integrated photovoltaics application.

(Invited) Small Yet Bright Lanthanide-Based Nanoparticles Via Rapid Microwave-Assisted Synthesis

Based on their outstanding optical properties, lanthanide-based compounds have been suggested for a wide range of applications including the fields of biomedicine, optoelectronics, and solar energy conversion. For instance, the capability of lanthanide-based materials to emit visible and near-infrared (NIR) light under NIR excitation is highly sought after when aiming for biomedical applications. This is as NIR light penetrates deeper into biological tissue and is less phototoxic than UV light commonly used for optical bioprobes. Our favorite nanomaterials are lanthanide-based fluorides (MLnF4, M = alkali metal, Ln = lanthanides and Yttrium), and our research addresses challenges in their synthesis as well as the establishment of structure-property relationships. The growing attention toward such optically active materials has prompted the development of novel synthesis methods for a more reliable and efficient access to these systems. In this regard, microwave-assisted approaches provide unique advantages over traditional solvothermal methods reliant on convectional heating: namely, significantly shorter reaction durations, more rigid reaction conditions, and thus a higher degree of reproducibility. Upon control of multiple physico-chemical reaction parameters – including the choice of precursors, the reaction temperature/time profile, and the metal ion to Ln3+ ion ratio – MLnF4 materials of tailored crystalline phase and size at the sub-10 nm realm can be obtained. Such control is crucial for the understanding of fundamental structure-property relationships and when aiming for the design of design of next-generation bioprobes and energy converters. For instance, the upconverting properties of the obtained nanomaterials render them suitable energy donors when combined with lanthanide-based complexes acting as energy acceptors. Key features of the resulting hybrid system are the simultaneous UV-blue and NIR light harvesting capabilities. These traits render the presented hybrid system a formidable candidate for the development of photoactivated devices capable of operating under multiple excitation wavelengths and to transduce the absorbed light into narrow, well-defined spectral regions.

Gold nanorods/g-C3N4 heterostructures for plasmon-enhanced photocatalytic H2 evolution in visible and near-infrared light

Recently, broad spectrum (visible and near-infrared (NIR)) light utilization has aroused widespread attention in the research of photocatalysis. While g-C3N4, highly stable, cheap and easily synthesized, shows H2 evolution activity under visible light irradiation, it doesn’t perform under NIR light irradiation. Here we report an Au nanorods (NRs)/g-C3N4 heterostructure with Au nanorods on g-C3N4’s surface. The most exciting feature of designed Au NRs/g-C3N4 heterostructures is that Au nanorods themselves are excited by visible and NIR light, which produce hot electrons and inject into g-C3N4. The photocatalytic H2 evolution rate of Au NRs/g-C3N4 heterostructures (350.6 μmol g−1 h−1) is nearly 4 times higher than that of g-C3N4 with Pt as cocatalyst (68.9 μmol g−1 h−1) under visible light illumination. The improved photocatalytic activity is ascribed to the increasing visible light-absorbing capacity of transverse surface plasmon resonance (TSPR) of Au nanorods and improved charge separation of Au NRs/g-C3N4 heterostructure. Even more important, Au NRs/g-C3N4 heterostructures achieve NIR photocatalytic H2 evolution performance (63.1 μmol g−1 h−1), owing to the longitudinal SPR (LSPR) effect of Au nanorods induced NIR light harvesting ability.

Surpassing the 10% efficiency milestone for 1-cm2 all-polymer solar cells

Naphthalenediimide-based n-type polymeric semiconductors are extensively used for constructing high-performance all-polymer solar cells (all-PSCs). For such all-polymer systems, charge recombination can be reduced by using thinner active layers, yet suffering insufficient near-infrared light harvesting from the polymeric acceptor. Conversely, increasing the layer thickness overcomes the light harvesting issue, but at the cost of severe charge recombination effects. Here we demonstrate that to manage light propagation within all-PSCs, a thick bulk-heterojunction film of approximately 350 nm is needed to effectively enhance photo-harvesting in the near-infrared region. To overcome the severe charge recombination in such a thick film, a non-halogenic additive is used to induce a well-ordered micro-structure that inherently suppresses recombination loss. The combined strategies of light management and delicate morphology optimization lead to a promising efficiency over 10% for thick-film all-PSCs with active area of 1 cm2, showing great promise for future large-scale production and application of all-PSCs.

Strategies Toward Extending the Near‐Infrared Photovoltaic Response of Perovskite Solar Cells

The emerging perovskite materials present great opportunities for cost‐saving and efficient photovoltaic devices. However, perovskite solar cells (PSCs) suffer from the limitation of short optical absorption edge, resulting in most of the near‐infrared (NIR) light being wasted. Recently, strategies toward broadening the NIR spectra response and further improve the power conversion efficiency of PSCs have attracted extensive attention. In this review, the unique features of perovskite materials are first introduced; subsequently, the current developments of organic–inorganic hybrid PSCs and all‐inorganic PSCs are highlighted. Then, a detailed summary of the strategies toward enhancing the NIR light harvesting of PSCs, namely, perovskite/Si and perovskite/Cu(In1–x, Gax)Se2 tandem solar cells (TSCs) and the integrated perovskite/organic solar cells (IPOSCs), is presented. After an in‐depth understanding of the working mechanism of TSCs and IPOSCs, a comprehensive overview about their recent developments, key detrimental factors restricting their further performance enhancement, and feasible countermeasures to conquer these scientific and technological problems are given. In the end, the perspectives on the related materials and devices are addressed.

Improvement of Photostability and NIR Activity of Cyanine Dye through Nanohybrid Formation: Key Information from Ultrafast Dynamical Studies.

Near-infrared (NIR) light harvesting has enormous importance for different potential applications in the modern era of research. Some NIR cyanine dyes such as IR820 have achieved great success in energy harvesting and cancer therapy. However, their action is limited for low photostability, considerable thermal degradation, short circulation times, and nonspecific biodistribution. Our present study is an attempt to overcome such limitations by attaching a model cyanine dye IR820 with ZnO nanoparticles. We prepared an IR820-ZnO nanohybrid and characterized it using microscopic and optical spectroscopic tools. Thermogravimetric analysis depicted greater thermal stability of the IR820-ZnO nanohybrid compared to free dye. We explored the enhancement in the photostability of IR820 upon nanohybrid formation. We detected generation of photoinduced reactive oxygen species (ROS) such as superoxide, singlet oxygen, and so forth using appropriate molecular probes. The formation of IR820-ZnO nanohybrid reduced production of photoinduced singlet oxygen. However, it revealed an alternative trend in overall ROS formation (increases total ROS) under red light illumination. To correlate the enhanced photostability of IR820 on the ZnO surface, we explored excited-state dynamical processes at the interface in nanohybrids. We illustrated the photoinduced excited-state electron-transfer process from the lowest unoccupied molecular orbital of IR820 to the conduction band of ZnO. This photoelectron-transfer process enhances the production of ROS and decreases the formation of singlet oxygen that altogether leads to improvement in photostability and overall activity. A quencher of singlet oxygen sodium azide (NaN3) was used to further confirm the direct association of singlet oxygen generation with the photostability issue of IR820. Also, ZnO is able to deliver the dye selectively in acidic environment, which suggests its diseased site-specific targeted activity. Our results provide promising improvement for potential use of IR820 through formation of a nanohybrid that could be translated for other NIR cyanine dyes.

A chlorinated non-fullerene acceptor for efficient polymer solar cells

Improving the performance and reducing the manufacturing costs are the main directions for the development of organic solar cells in the future. Here, the strategy that uses chemical structure modification to optimize the photoelectric properties is reported. A new narrow bandgap (1.30 eV) chlorinated non-fullerene electron acceptor (Y15), based on benzo[d][1,2,3] triazole with two 3-undecyl-thieno[2′,3′:4,5] thieno[3,2-b] pyrrole fused -7-heterocyclic ring, with absorption edge extending to the near-infrared (NIR) region, namely A-DA'D-A type structure, is designed and synthesized. Its electrochemical and optoelectronic properties are systematically investigated. Benefitting from its NIR light harvesting, the fabricated photovoltaic devices based on Y15 deliver a high power conversion efficiency (PCE) of 14.13%, when blending with a wide bandgap polymer donor PM6. Our results show that the A-DA'D-A type molecular design and application of near-infrared electron acceptors have the potential to further improve the PCE of polymer solar cells (PSCs).

Optimizing concurrent extension of near-infrared and ultraviolet light harvesting of dye sensitized solar cells by introducing sandwich-nanostructured upconversion-core/inert-shell/ downconversion-shell nanoparticles

Simultaneous realization of upconversion (UC) and downconversion (DC) processes in a single unit provides unique opportunities of photons utilization throughout a broad spectral range for dye-sensitized solar cells (DSSCs). Yet, the existence of cross relaxation quenching effect in UC/DC interface causes a low synergistic effect. Here, we propose a strategy of embedding an inert layer to spatially separate active UC and DC layers at precisely defined thickness. The construction of sandwich-nanostructured NaYF4:20%Yb3+,2%Er3+@NaLuF4@NaYF4:15%Eu3+ allows the elimination of detrimental cross relaxation quenching, implementing optimal synergistic effect of UC/DC system and further extending simultaneous near-infrared (NIR) and ultraviolet (UV) absorption of DSSC devices to the most extend. By incorporating the sandwiched UC-core/inert-shell/DC-shell nanoparticles into the TiO2 photoanode of DSSCs, the increased photon-electron conversion efficiency (PCE) of 7.87% was obtained mainly by the increased photocurrent of 14.93 mA/cm2 due to the concurrent NIR and UV light harvesting enhancement (PCE = 6.73%, Jsc = 11.91 mA/cm2 for the control cell without the sandwiched spectral layer), thus, showing a noticeable PCE enhancement ratio of ∼16.94%. This work provides a promising strategy to integrate various photons processes in one single unit and broaden spectral respond toward high-efficiency solar cell systems.