Active Layer Of Organic Solar Cells Research Articles

Morphology Optimization by Non-Halogenated and Twisted Volatile Solid Additive for High-Efficiency Organic Solar Cells.

Recently, volatile solid additives have attracted tremendous interest in the field of organic solar cells (OSCs), which can effectively improve device efficiency without sacrificing the reproducibility and stability of the device. However, the structure of reported solid additives is onefold and its working mechanism needs to be further investigated. Herein, a novel non-halogenated and twisted solid additive 1,4-diphenoxybenzene (DPB) is employed to optimize the morphology of the active layer in OSCs. The properties of additive DPB, morphology of active layer, and carrier dynamics behaviors have been systematically investigated through theoretical calculations, in situ and ex situ spectroscopy, grazing-incidence wide-angle X-ray scattering (GIWAXS), and grazing-incidence small-angle X-ray scattering (GISAXS) measurement, as well as ultrafast spectroscopy technology. The results reveal that the twisted additive DPB selectively interacts with acceptor Y6, and thus forms optimized morphology of active layer with increased molecular crystallinity, tight molecular packing, and favorable phase separation. As a result, the optimized devices deliver a remarkable power conversion efficiency (PCE) of 19.04%, which is the highest value for the D18-Cl:N3 system to date. These results demonstrate that non-halogenated and twisted solid additive DPB has broad prospects in the preparation of highly efficient OSCs, providing theoretical and experimental guidance for the development of high-performance solid additives.

To Maximize Luminescence for an Efficient Organic Solar Cell†

Comprehensive SummaryWith the continuous development of photovoltaic materials, organic solar cells (OSCs) have made remarkable advancements, surpassing a power conversion efficiency (PCE) of 20%. However, the PCEs of OSCs remain lower than that of inorganic solar cells due to significant energy losses, mainly stemming from the relatively large non‐radiative recombination losses (usually be expressed as ∆E3), resulting in low open‐circuit voltages. This can be achieved by reducing non‐radiative recombination, and hereby increasing the electroluminescence quantum efficiency (EQEEL) of the photo‐active layer. This review analyzes the significance of luminescence efficiency in achieving high‐performance OSCs by examining the reciprocal relationship between ∆E3 and EQEEL. High‐efficiency organic solar cells can also be used as effective organic light‐emitting diodes (OLEDs). The discussion provides insights into the influencing factors of EQEEL and the mechanisms for adjusting various parameters, which include enhancements in photoluminescence quantum yield and the proportion of radiative excitons. The objective is to offer insights into the crucial role of luminescence performance in OSC development, guiding researchers toward developing novel photovoltaic materials or optimization strategies to enhance the luminescence performance of the active layer in OSCs, fostering the simultaneous advancement of OSCs and OLEDs. Key Scientists

A high-efficiency clay mineral based organic photocatalyst towards photodegradation of butyl xanthate in mineral processing wastewater

The organic solar cell active layer, well known for excellent visible light response capability, is regarded as a potential candidate for photocatalytic degradation of organic wastewater. However, the poor dispersibility in water due to its hydrophobicity property severely limited the degrading efficiency. In this work, a novel composite photocatalyst PM6:IDT8CN-M/CK2 with a broad visible absorption spectrum and non-toxicity was first synthesized through the intercalation compounding method. A good dispersibility of PM6:IDT8CN-M in wastewater was achieved with the help of rich interlamellar porosity and good hydrophilicity of calcined kaolin. This composite photocatalyst was successfully applied to the SBX photocatalytic degradation in mineral processing wastewater, and the SBX pollutants can be completely degraded within 10 min under the condition of visible light irradiation. Compared with other reported photocatalysts, the photocatalytic degradation efficiency of SBX was dramatically improved by at least seven times. Moreover, PM6:IDT8CN-M/CK2 has remarkable stability, sustaining degradation efficiencies of over 90 % in 60 cycles. Notably, the organic solar cell active layer in PM6:IDT8CN-M/CK2 can achieve carrier rapid separation and transport, enhancing the generation of active oxides (∙O2–, and ∙OH, etc.). At the same time, the large surface area of PM6:IDT8CN-M/CK2 provides a suitable environment for the oxidation reaction of active radicals with SBX to achieve this efficient photocatalytic degradation. Overall, this work not only extends the application scope of organic solar cell active layer, but also develops a high-efficiency SBX removal technique for the treatment of mineral processing wastewater.

(Invited) Development of Non-Fused Nonfullerene Acceptors Bearing Spiro-Substituted Structures and Application to Green-Light Wavelength-Selective Organic Solar Cells

Organic solar cells (OSCs) have been extensively investigated as next-generation energy sources due to their potential for large-area fabrication, light weight, flexibility. The active layer of OSCs is composed of a blend of donors and acceptors, which form bulk heterojunction structures in the films. The development of A-D-A-type nonfullerene acceptors (NFAs) with large fused-ring donor structures have significantly accelerated OSC research. On the other hand, non-fused electron-accepting p-conjugated compounds have been investigated recently for application to NFAs. In this presentation, we focus on cyclopentene-annelated thiophene with spiro-substituted 2,7-bis(2-ethylhexyl)fluorene (FT) as a rigid and sterically bulky linker unit and develop a non-fused NFA containing FT units. We also focus on the development spiro-substituted NFAs with green-light wavelength-selective absorbance. The combination of these acceptors and poly(3-hexylthiophene) can produce green-light wavelength-selective OSCs for application in new greenhouse agrivoltaics.

A Non‐Halogenated Polymer Donor Based on Imide Unit for Organic Solar Cells with Efficiency Nearly 16%

Comprehensive SummaryNon‐halogenated polymers have great potential in the commercialization of organic solar cells (OSCs) due to their advantages in the manufacturing process. However, high‐performance donor polymers are limited to a small amount of building blocks. Herein, we utilize as building block 4H‐dithieno[3,2‐e:2',3'‐g]isoindole‐4,6(5H)‐dione (DTID) to design and synthesize a relevant non‐halogenated polymer PBTID for active layers in OSCs. PBTID exhibits a strong absorption in the wavelength range of 400—600 nm with a distinctly wide optical bandgap of 2.06 eV, a low‐lying highest occupied molecular orbital (HOMO) energy level of −5.53 eV. In addition, this polymer has a very strong aggregation effect in solution and could form nanoscale fibrils in the neat film. Consequently, when blended with the non‐fullerene acceptor Y6, the devices achieve a prominent PCE of 15.8% with a high Voc of 0.87 V. The Voc and PCE values are one of the highest values in the non‐halogenated polymer donor‐based OSCs reported to date.

A follow-up investigation: Organic solar cells based on chalcogenophene-Thieno[3,4-c]pyrrole-4,6-dione-chalcogenophene containing random conjugated polymers

Herein, we conducted a comprehensive comparison between fullerene (FA) and non-fullerene (NFA) acceptor-based organic solar cells (OSCs). Four chalcogenophene-thieno[3,4-c]pyrrole-4,6-dione-chalcogenophene containing random conjugated polymers were used as donor materials in the active layer of OSCs. Our results showed that selenophene-containing polymer P1 performed better with ITIC (NFA), resulting in a PCE of 7.94%, whereas when blended with PC71BM (FA), it performed a PCE of 7.62%. One other selenophene containing polymer P2 achieved a PCE of 1.96% with ITIC and 6.30% with PC71BM. P3 and P4 (furan-containing polymers) exhibited 1.40% and 1.32% with ITIC, whereas when blended with PC71BM, 1.46% and 2.45%, respectively.

Designing efficient A-D-A1-D-A type fullerene free acceptor molecules with enhanced power conversion efficiency for solar cell applications

The achievement of highly efficient power conversion efficiency (PCE) is a big concern for non-fullerene organic solar cells (NF-OSCs) because PCE can depend on numerous variables. Here, new five novel acceptor molecules without fullerenes were developed and investigated using DFT (density functional theory) and TD-DFT (time dependent-density functional theory). Compared to the recently synthesized molecule (PZ-dIDTC6), the developed molecules display a narrow optical band gap, exhibiting a red shift in the absorption spectrum. The developed molecules (YM1-YM5) express high mobility of electrons and holes in the active layer of OSCs (organic solar cells). In addition, high open-circuit voltage (Voc) values with maximum charge density shifting are noted in designed molecules. YM1-YM5 is also associated with low binding energy and excitation energy. This work proves that noncovalent conformational locking is favourable for improving PCE devices.

Development of regio-regular poly(3-hexylthiophene) by direct arylation using Fagnou's conditions.

Semiconducting polymers are widely studied due to their applications in photovoltaic devices, the predominant conjugated polymer used in organic solar cells (OSCs) is semicrystalline poly(3-hexylthiophene) P3HT, which can be produced by easy, low-cost and environmentally friendly methods such as direct arylation polymerization (DArP) (N.S. Gobalasingham et al. 2018). Due to its solution processing, deposition on different types of substrates, even flexible, with technologies such as spin coating and roll to roll, it is a feasible option for large-scale production. In this work we present the synthesis, physicochemical characterization of a regio- regular P3HT by the direct arylation method using Fagnou conditions and its evaluation on the active layer of OSCs with bulk heterojunction architecture.

Mixed molecular orientations promote charge transport in bulk heterojunction solar cells.

By systematically varying the molecular orientation of poly(3-hexylthiophene-2,5-diyl) (P3HT) in P3HT:fullerene bulk heterojunctions, we show that a mixed face-on and edge-on texture can be beneficial for out-of-plane charge flow in solution processed organic bulk heterojunction solar cells. These results implicate the need to balance in-plane and out-of-plane pathways for efficient charge percolation in bulk heterojunctions.

A comparative study of low-cost coating processes for green & sustainable organic solar cell active layer manufacturing

Owing to their facile integration into existing commercial products, high volume manufacturing of organic solar cells (OSCs) can be expected in the upcoming years. Therefore, it is important to evaluate the performance and sustainability of various active layer coating methods for OSCs. Herein, we compare four active layer coating processes: spin-coating, blade-coating, spray-coating and push-coating for poly(2,7-carbazole-alt-dithienylbenzothiadiazole):[6,6]-Phenyl-C71-butyric acid methyl ester (PCDTBT:PC71BM) active layers deposition. The optical, morphological and photovoltaic parameters of the active layers are studied. The suitability of each coating method for industrial manufacturing of PCDTBT:PC71BM OSCs is discussed in terms of environmental impact, necessary investments and running costs. Our results confirm that, despite producing high quality and high performance OSCs, spin-coating is unsuitable for high volume manufacturing due to the large amounts of materials and hazardous solvents wasted in the process. Blade-coating provides a good balance between low running costs, low environmental impact and decent performances but the process introduces lateral compositional gradients which could be detrimental for large area OSC processing. Spray-coating requires minimal initial investments but has relatively low performance and low manufacturing sustainability. Push-coating yields OSCs which perform as well as spin-coated ones, with a much lower environmental impact and cost. We should thus look forward to seeing whether this green and sustainable technology can develop into a large area coating process in the future.

Identifying tunneling effects of poly(aryl ether) matrices and boosting the efficiency, stability, and stretchability of organic solar cells

Tunneling effects are one of the most basic theories that have long been overlooked in the bulk-heterojunction (BHJ) layers of organic solar cells (OSCs). Herein, by fabricating BHJ and layer-by-layer (LbL) devices with five different poly(aryl ether)s (PAEs), we reveal a tunneling effect in the active layer of OSCs. The results show that the as-cast devices with 5 wt % and even 30 wt % PAE in PM6:Y6-blends achieve high power conversion efficiencies (PCEs) over 15%. Furthermore, the 5 wt % PAE-based devices with proper post-treatment deliver a PCE of 17.03%. By inserting a thin PAE layer with high dielectric constant, the LbL OSCs (PM6/PAE-237/Y6) yield a 23% improvement PCE compared to one without PAEs. With rational molecular design, we demonstrate that heat-resistant PAE matrices with high stretchability simultaneously improve efficiency, stability, and mechanical flexibility of OSCs. The proposed tunneling effect and PAE matrices strategy have important implications for fabricating efficient, stable, and flexible organic devices.

Pseudo-bilayer architecture enables high-performance organic solar cells with enhanced exciton diffusion length

Solution-processed organic solar cells (OSCs) are a promising candidate for next-generation photovoltaic technologies. However, the short exciton diffusion length of the bulk heterojunction active layer in OSCs strongly hampers the full potential to be realized in these bulk heterojunction OSCs. Herein, we report high-performance OSCs with a pseudo-bilayer architecture, which possesses longer exciton diffusion length benefited from higher film crystallinity. This feature ensures the synergistic advantages of efficient exciton dissociation and charge transport in OSCs with pseudo-bilayer architecture, enabling a higher power conversion efficiency (17.42%) to be achieved compared to those with bulk heterojunction architecture (16.44%) due to higher short-circuit current density and fill factor. A certified efficiency of 16.31% is also achieved for the ternary OSC with a pseudo-bilayer active layer. Our results demonstrate the excellent potential for pseudo-bilayer architecture to be used for future OSC applications.

Quantitative insights into the phase behaviour and miscibility of organic photovoltaic active layers from the perspective of neutron spectroscopy

Neutron spectroscopy as a master microscopic probe of the composition-dependent phase behaviour and miscibility of organic solar cell active layers.

Water-Processed Organic Solar Cells with Open-Circuit Voltages Exceeding 1.3V

Conjugated polyelectrolytes are commonly employed as interlayers to modify organic solar cell (OSC) electrode work functions but their use as an electron donor in water-processed OSC active layers has barely been investigated. Here, we demonstrate that poly[3-(6’-N,N,N-trimethyl ammonium)-hexylthiophene] bromide (P3HTN) can be employed as an electron donor combined with a water-soluble fullerene (PEG-C60) into eco-friendly active layers deposited from aqueous solutions. Spin-coating a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) layer prior to the P3HTN:PEG-C60 active layer deposition considerably increases the open-circuit voltage (Voc) of the OSCs to values above 1.3 V. Along with this enhanced Voc, the OSCs fabricated with the PEDOT:PSS interlayers exhibit 10-fold and 5-fold increases in short-circuit current density (Jsc) with respect to those employing bare indium tin oxide (ITO) and molybdenum trioxide coated ITO anodes, respectively. These findings suggest that the enhanced Jsc and Voc in the water-processed OSCs using the PEDOT:PSS interlayer cannot be solely ascribed to a better hole collection but rather to ion exchanges taking place between PEDOT:PSS and P3HTN. We investigate the optoelectronic properties of the newly formed polyelectrolytes using absorption and photoelectron spectroscopy combined with hole transport measurements to elucidate the enhanced photovoltaic parameters obtained in the OSCs prepared with PEDOT:PSS and P3HTN.

Insulating Polymers for Enhancing the Efficiency of Nonfullerene Organic Solar Cells

A series of insulating polymers are used as additives in nonfullerene organic solar cells (OSCs) for the first time. A significant relative power conversion efficiency (PCE) enhancement of up to 16% is observed with an introduction of polystyrene for only 5.0 wt% into the active layer of OSCs. Other insulating polymers possessing linear nonconjugated backbones with different side chains are also incorporated into OSCs and the resultant PCE enhancement decreases with the decrease in the side chain size. Another important issue that is noted is the glass transition temperature of the polymer additive. When the glass transition temperature is higher than the thermal annealing temperature of the active layer, the polymer additive plays a negative effect on the device performance and the device efficiency decreases monotonically with the increase in addition amount. So the effect of the insulating polymer additives in nonfullerene OSCs can be attributed to the reconstruction of the active layer films, which increases the crystallinity, carrier mobility, and carrier lifetime of the organic semiconductors in the bulk heterojunction of the devices. This work provides a guideline for the selection of polymer additives in OSCs apart from the consideration on the optoelectronic property of the additives.

Air-processed active-layer of organic solar cells investigated by conducting AFM for precise defect detection.

Atmospheric processing of organic solar cells (OSCs) has already emerged and will be a challenge to emulate with the existing market leaders in terms of overall cost reduction and large scale production. However, the presence of defects in the active layer of OSC needs to be identified effectively to minimize the performance degradation involved. In this work, conventional bulk-heterojunction (BHJ) OSCs are fabricated entirely in air having an efficiency (η) up to 4.0% using P3HT and PC61BM as the donor and acceptor, respectively. The devices have exhibited reasonable degradation of performance parameters with aging time and uninterrupted illumination during characterization in ambient air. This visible degradation was as expected because of environmental oxygen and moisture penetration into the photoactive layer through the defects, which can be prevented by immediate encapsulation. Conducting AFM is utilized here to visualize these defects more prominently, which are impossible to see in typical AFM topography. Overall, significant development of atmospheric processing of BHJ OSCs is made, and performance stability is also studied to bring down the fabrication costs in the near future.

Using Solubility Parameters to Model More Environmentally Friendly Solvent Blends for Organic Solar Cell Active Layers.

To facilitate industrial applications, as well as for environmental and health purposes, there is a need to find less hazardous solvents for processing the photoactive layer of organic solar cells. As there are vast amounts of possibilities to combine organic solvents and solutes, it is of high importance to find paths to discriminate among the solution chemistry possibilities on a theoretical basis. Using Hansen solubility parameters (HSP) offers such a path. We report on some examples of solvent blends that have been found by modelling HSP for an electron donor polymer (TQ1) and an electron acceptor polymer (N2200) to match solvent blends of less hazardous solvents than those commonly used. After the theoretical screening procedure, solubility tests were performed to determine the HSP parameters relevant for the TQ1:N2200 pair in the calculated solvent blends. Finally, thin solid films were prepared by spin-coating from the solvent blends that turned out to be good solvents to the donor-acceptor pair. Our results show that the blend film morphology prepared in this way is similar to those obtained from chloroform solutions.

In-Plane Pathways Facilitate Out-of-Plane Charge Transport in Organic Solar Cell Active Layers

Solution-processed organic bulk heterojunctions are promising for enabling low-cost, lightweight, and mechanically flexible solar cells. While the nanostructured interpenetrating donor–acceptor morphology in bulk heterojunctions leads to efficient charge photogeneration, the locally varying composition, crystallinity, and electrical connectivity result in a complex landscape for charge transport. This work examines the structural features that govern out-of-plane charge transport in a high-performance small molecule:fullerene organic photovoltaic system, 7,7-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b]dithiophene-2,6-diyl)bis(6-fluoro-4-(5-hexyl-[2,2-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole) (p-DTS(FBTTh2)2) blended with phenyl-C71-butyric acid methyl ester (PC71BM). Active layer composition and degree of donor–acceptor phase separation were systematically varied and characterized electrically by conductive atomic-force-microscope-based charge carrier mobility mapping and structurally by grazing incid...

Electrospray-deposited vanadium oxide anode interlayers for high-efficiency organic solar cells

Abstract Spray coating, in competition with conventional spin coating, has attracted extensive attention among large-scale solution casting techniques for producing high-performance organic solar cell (OSC) devices. Solution-processed vanadium oxide (VOx) is used extensively as an anode interlayer (AIL) in OSCs because of its unique optical and electronic properties. In this study, we optimized VOx AILs prepared using electrospray deposition (ESD-VOx) and compared them with AILs prepared using spin coating (SC-VOx); various ESD-VOx properties were found to be optimized at a flow rate of 6.25 μL/min. The OSC active layer used was poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl3- fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-bthiophenediyl): [6,6]phenyl-C71-butyric acid methyl ester (PTB7:PC71BM). The ESD-VOx devices had transmittance and surface morphology comparable to SC-VOx interlayers used in high-efficiency OSC devices. X-ray photoelectron spectroscopy indicated that the obtained ESD-VOx surfaces had a favorable chemical composition. Measurement of hole mobilities using the space charge limited current method showed values of 4.36 × 10−4 and 1.39 × 10−4 cm2 V−1 s−1 for ESD- and SC-VOx, respectively. The charge transport resistance, measured by impedance spectroscopy, was very low for ESD-VOx devices, indicating that there faster charge transportation occurs within these devices because of enhanced hole mobility. These data are consistent with the carrier lifetimes of 1.59 × 10−8 and 4.53 × 10−4 s for ESD- and SC-VOx, respectively. The enhanced charge transportation properties, which can reduce charge recombination, can be attributed to the advantageous surface and interfacial properties of ESD-VOx AILs. Results indicate that optimized ESD had unperturbed diode characteristics with an improved power conversion efficiency, compared to spin coated VOx, of 7.61%.

有机太阳能电池活性层材料

有机太阳能电池活性层材料