High-efficiency Polymer Solar Cells Research Articles

Unveiling the Influence of Linkers on Conformations of Oligomeric Acceptors for High-Performance Polymer Solar Cells.

Conformational isomerism of organic photovoltaic materials has a profound impact on their molecular packing and therefore performance of polymer solar cells (PSCs). However, the conformations of oligomeric acceptors (OAs) are mostly predicted by simulations rather than experimental determinations. Herein, the stereochemical S-shaped structure of two dimeric-type acceptor molecules, V-DYIC and V-DYIC-4F, is first confirmed with different end groups (IC for V-DYIC and IC-2F for V-DYIC-4F), incorporating vinylene linkage for connecting the distinct state-of-the-art small molecule acceptor Y-segments. Through the synthetic control of fluorination sites adjacent to the vinyl-linker, S-shaped the conformation by NMR experiments is validated. Compared to the O-shaped dimer, S-shaped conformation results in enhanced lamellar order and reduced nonradiative recombination losses. The optimal acceptor, V-DYIC-4F, achieved a champion efficiency of 18.10% with the lowest energy loss of 0.556eV in its devices paired with PM6 due to their efficient carrier transport, and suppressed recombination compared to other devices, being attributed to the synergistic effect of conformation and end group fluorination. The insights gained in this work contribute valuable knowledge of both synthetic control and structural determination of OAs, providing strategic design guidelines for the future development of dimeric acceptors toward high-efficiency PSCs.

A benzobisoxazole-based polymer assisting high efficiency polymer solar cells

Ternary strategy is an effective method to optimize photovoltaic process and improve device performance. In this work, a benzobisoxazole-based conjugated polymer PBBO was designed and employed as the guest component for PM6:BTP-eC9 based devices. The polymer PBBO shows a large band gap of 2.16 eV and strong photoluminescence property, with efficient energy transfer observed between PBBO and PM6. The ternary blends not only form a cascaded energy level distribution, but also an alloy-like structure, which can effectively promote the exciton dissociation, charge transfer and efficiently suppress charge recombination. As a result, the power conversion efficiency (PCE) of the ternary device is substantially improved from 17.50% to 18.66% with the incorporation of PBBO guest component. Meanwhile, the ternary device shows good stability with retaining 86% of initial efficiency after storage for 2000 hours. This research demonstrates that the polymer PBBO would be an excellent photovoltaic material to optimize the performance of polymer solar cells.

Analysis of the degradation of highefficiency encapsulated PM6:Y7based Photovoltaic Cells

In this work, we report a degradation study of high-efficiency conventional polymer solar cells (PSCs). The high performance of the PM6:Y7-based device is achieved with a power conversion efficiency (PCE) of up to 15.64% in the first measurement. The article describes the results of the measurements and analysis of the degradation process. The electrical parameters during the degradation process were extracted from the current density – voltage characteristics curves (J–V) under light and dark conditions. Were observed the specific parameters of the selected cells: open-circuit voltage (VOC), short circuit current density (JSC), fill factor (FF), PCE, series (RS), and shunt (RSH) resistance values The PCE of the device decreased down to 64% of the initial PCE after 1056 h.

An Isomeric Solid Additive Enables High-Efficiency Polymer Solar Cells Developed Using a Benzo-Difuran-Based Donor Polymer.

Currently, nearly all high-efficiency organic photovoltaic devices use donor polymers based on the benzo-dithiophene (BDT) unit. To diversify the choices of building blocks for high-performance donor polymers, the use of benzo-difuran (BDF) units is explored, which can achieve reduced steric hindrance, stronger molecular packing, and tunable energy levels. In previous research, the performance of BDF-based devices lagged behind those of BDT-based devices. In this study, a high efficiency (18.4%) is achieved using a BDF-based polymer donor, which is the highest efficiency reported for BDF donor materials to date. The high efficiency is enabled by a donor polymer (D18-Fu) and the aid of a solid additive (2-chloronaphthalene), which is the isomer of the commonly used additive 1-chloronaphthalene. These results revealed the significant effect of 2-chloronaphthalene in optimizing the morphology and enhancing the device parameters. This work not only provides a new building block that can achieve an efficiency comparable to dominant BDT units but also proposes a new solid additive that can replace the widely used 1-chloronaphthalene additive.

A simple doping strategy to improve PEDOT:PSS charge extraction capability in polymer solar cells

Black Phosphorus (BP) has shown great potential in optoelectronic devices due to its remarkable semiconductor properties. Herein, liquid-exfoliated BP nanosheets is doped into poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) to form a hybrid hole transport layers (HTLs). The incorporation of BP nanosheets in PEDOT:PSS dramatically changes the nanostructure and electrical conductivity of film. The BP doped PEDOT:PSS HTLs possess excellent charge selectivity and transport capability, which are proved in non-fullerene and fullerene blend system based polymer solar cells (PSCs). Furthermore, the nanostructure of PM6:Y6 light absorber changes a lot after introduction of BP nanosheets. Thus, weak charge recombination loss, high exciton generation rate and dissociation probability, and low transport resistance are observed in BP nanosheets doped PEDOT:PSS HTLs based cells, which result in improved power conversion efficiency (PCE). As a result, significant improvement of PCE (>18%) is observed in both non-fullerene and fullerene blend systems based cells. This result demonstrates a simple and effective strategy to form efficient HTLs in high-efficiency PSCs.

Non-Halogenated Solvent-Processed High-Efficiency Polymer Solar Cells: the Role of Diphenyl Ether in Morphology, Light-Trapping, Transport Properties

Non-Halogenated Solvent-Processed High-Efficiency Polymer Solar Cells: the Role of Diphenyl Ether in Morphology, Light-Trapping, Transport Properties

The effect of boron-doped carbon nanotubes blended with active layers in achieving high-efficiency polymer solar cells and X-ray detectors

Polymer solar cells (PSCs) usually offer inferior power conversion efficiency (PCE), lower open-circuit voltage (Voc), and inefficient charge extraction abilities. We studied boron-doped carbon nanotubes (B-CNTs) as the third active layer (AL) component to improve the PCE and Voc, due to their tunable work function, superior conductivity, and transport behavior. A novel arc discharge (AD) method produced B-CNTs without any residual catalysts. This work utilized PBDB-T: ITIC as the initial AL to prepare PSCs and X-ray detectors with glass/ITO/PEDOT: PSS/AL/LiF/Al structure. The excitation effects of PSC and X-ray detector devices based on ALs embedded with different amounts of B-CNTs were also studied. The derived outcomes revealed a PCE of 10.21 % for the constructed PSC with 3 wt% of B-CNTs blended AL. Furthermore, the fabricated X-ray photodetector with 3 wt% of B-CNTs obtained an excellent sensitivity of 2.49 mA/Gy·cm2. These results show that B-CNTs can act as both an exciton dissociation center and a charge transfer channel, promoting charge separation and transport in the AL.

High efficiency polymer solar cells sensitized by red-emitting ZnCuInS nanoplatelets

We synthesized the two-dimensional Zn–Cu–In–S (ZCIS) semiconductor nanoplatelets and then modified their surface with 4-bromobenzenediazonium tetrafluoroborate. The surface modified ZCIS nanoplatelets were combined with the conventional photovoltaic hole transport layer material (HTL) PEDOT: PSS. The work function of the HTL increased from 5.04 eV to 5.17 eV, thus promoting the reduction of the energy potential barrier and increasing the internal electric field. It also effectively improves the light utilization by effectively increasing the absorption of light in the spectral range below 500 nm and converting them into the secondary emission in the 600–700 nm range. Such emission can be effectively utilized by the active layer to increase the open-circuit voltage (Voc) and short-circuit current (Jsc) of the cell, resulting in an increase in the overall cell power conversion efficiency (PCE) from 12.29%–13.14%.

Non-halogenated solvent processable wide bandgap polymer based on carboxylate-substituted benzodithiophene for high-efficiency polymer solar cells

The use of non-halogenated solvents for the fabrication of polymer solar cells (PSCs) is a crucial step for commercial applications in the future. Herein, we synthesize a wide bandgap polymer PBDT-ST with alkylthio chains substituted benzodithiophene (BDT) as donor unit and carboxylate-substituted BDT as acceptor unit. The polymer PBDT-ST possesses a wide bandgap over 1.90 eV and a deep highest occupied molecular orbitals (HOMO) levels below −5.50 eV, which is beneficial to obtain a high open circuit voltage (Voc). In addition, PBDT-ST shows good solubility in halogenated and non-halogenated solvents. The o-xylene processed PBDT-ST:ITIC-2F blend film exhibits improved molecular order, film morphology and charge mobilities compared with o-dichlorobenzene (o-DCB) processed one. As the results, the o-DCB processed PBDT-ST:ITIC-2F based device can achieve a power conversion efficiency (PCE) of 10.48%. When the non-halogenated o-xylene as solvents and non-halogenated diphenyl ether (DPE) as additive, an improved PCE of 11.14% can be obtained with Voc of 0.90 V, Jsc of 17.83 mA/cm2 and FF of 69.36%. Our research indicates that carboxylate-substituted BDT based polymer PBDT-ST as a promising wide bandgap donor material can achieve excellent photovoltaic performance for PSCs processed by non-halogenated solvent.

Charge Photogeneration and Recombination in Fluorine-Substituted Polymer Solar Cells.

In this contribution, we studied the effect of fluorine substitution on photogenerated charge generation, transport, and recombination in polymer solar cells. Two conjugated polymer materials, PBDTTT-E (fluorine free) and PTB7 (one fluorine substitution), were compared thoroughly. Meanwhile, various characterization techniques, including atomic force microscopy, steady-state spectroscopy, transient absorption spectroscopy, spectroelectrochemistry, and electrical measurements, were employed to analyse the correlation between molecular structure and device performance. The results showed that the influence of fluorine substitution on both the exciton binding energy of the polymer and the carrier recombination dynamics in the ultrafast timescale on the polymer was weak. However, we found that the fluorine substitution could enhance the exciton lifetime in neat polymer film, and it also could increase the mobility of photogenerated charge. Moreover, it was found that the SOMO energy level distribution of the donor in a PTB7:PC71BM solar cell could facilitate hole transport from the donor/acceptor interface to the inner of the donor phase, showing a better advantage than the PBDTTT-E:PC71BM solar cell. Therefore, fluorine substitution played a critical role for high-efficiency polymer solar cells.

The Effect of Boron-Doped Carbon Nanotubes Blended Active Layer on Achieving High-Efficiency Polymer Solar Cells and X-Ray Detectors

The Effect of Boron-Doped Carbon Nanotubes Blended Active Layer on Achieving High-Efficiency Polymer Solar Cells and X-Ray Detectors

Water‐Induced Formation of α‐MoO3 Microcrystals as Anode Buffer Layer for Highly Efficient Polymer Solar Cells

Interfacial modification is an effective method to improve the performance of polymer solar cells (PSCs), and molybdenum oxide is one of the most widely used anode buffer layer (ABL) materials in PSCs. However, the complicated preparations with high‐temperature annealing or vacuum deposition make it uneconomic. Herein, a facile method to prepare MoOx solution in 1‐hexanol is proposed, and the component of the product can be simply adjusted by controlling the amount of introduced water. The added water facilitates the generation of α‐MoO3 microcrystals. To the best of our knowledge, this is also the first report to obtain α‐MoO3 through such a simple method. The obtained MoOx solutions are utilized to fabricate ABL in high efficiency PSCs to improve the performance. High temperature treatment is omitted, while the PCEs of binary and ternary devices can be enhanced to 16.09% and 16.81%, respectively, significantly higher than the devices with PEDOT:PSS ABL (15.55% and 15.93%). Herein, an efficient method to prepare MoOx solution in 1‐hexanol with controlled component is offered, and it is demonstrated that the MoOx ABL derived from the MoOx solution is a potential replacement to enhance the performance of high efficiency PSCs.

Non-conjugated natural alginate as electron-transport layer for high performance polymer solar cells after modification

The search for the alternatives to expensive synthesized conjugated polymers as interfaces in polymer solar cells (PSCs), which could largely decrease the cost and promote the commercialization process of PSCs, is now highly relevant. To introduce natural polymer as the interface layer for the high-efficiency PSCs would be a potential choice. In this study, a purely natural polysaccharide from ocean without any conjugated structure, sodium alginate (SA), is utilized as efficient electron transport layer (ETL) to replace the conjugated star molecule, poly [(9,9-bis(3'-(N,NdiMethyl)-NethylaMMoiniuM-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]dibroMide (PFN–Br), and modify the aluminum (Al) electrode in conventional PSCs. The reduction of the work function of Al is successfully achieved by SA forming a dipole and keeping the ohmic contact at the interface. Meantime, the ideal charge transfer and exciton dissociation are realized, along with decreasing charge recombination, resulting in a comparable power conversion efficiency (PCE) with devices of PFN-Br as ETL. For poly([2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b; 3,3-b]dithiophene]3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl):[6,6]-phenyl-C71-butyric acid methyl ester (PTB7-Th:PC71BM) system, PCE is increased to 9.5% and for Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithio-phene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c’]dithio-phene-4,8-dione)]:3,9-bis(2methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d']-s-indaceno[1,2-b:5,6-b'] dithiophene (PM6:IT-4F) system, PCE 13.4%, respectively, which illustrates a promising future for photovoltaic research of natural alginate non-conjugated polyelectrolyte in conventional PSCs.

Tuning the open circuit voltage by incorporating a diflurophenyl unit into a polymer backbone to achieve high efficiency polymer solar cells

Fabrication of high performance polymer solar cells using a ternary polymer system modulates the morphology of the active layer, and significantly enhances the Voc, Jsc, PCE and mobility values.

Designing a naphthyridinedione-based conjugated polymer for thickness-tolerant high efficiency polymer solar cells

A newly designed NTD-based polymer with an exceptionally high absorption coefficient, small crystallite size, and high charge mobility shows excellent thickness-tolerant high PCEs in fullerene PSCs.

A ligand-free direct heteroarylation approach for benzodithiophenedione-based simple small molecular acceptors toward high efficiency polymer solar cells

Simple fused-ring nonfullerene acceptor BDDEH with benzobithiophenedione as core unit is obtained through organostannane-free and ligand-free direct heteroarylation approach for the first time, which delivers a high efficiency of 12.59% in PSCs.

Comparative degradation analysis of V2O5, MoO3 and their stacks as hole transport layers in high-efficiency inverted polymer solar cells

The use of V2O5, MoO3 and their stacks as the buffer anode in organic solar cells greatly improves the lifetime of the photovoltaic devices, with a remaining PCE of over 50% of the initial PCE after 19 600 h (about 2 years).

High-efficiency ternary polymer solar cells with optimized morphology of active layers enabled by few-layered β-InSe nanosheets.

Due to the excellent electrical and optical properties, few-layered β-indium selenide (InSe) nanosheets are successfully introduced into the active layer of polymer solar cells (PSCs) as the third component for the first time. The addition of few-layered β-InSe nanosheets optimizes the absorption, crystallinity and vertical component distribution of the active layer. Compared with the binary devices, the ternary devices exhibit optimized bulk morphology and reduced charge recombination. The power conversion efficiency (PCE) of PSCs based on the PM6 : Y6 system is obviously improved from 15.02% to 16.56% due to the increasing short-circuit current and fill factor. The mechanism accounting for the morphological change in the ternary active layer is investigated in depth. Moreover, the efficacy of β-InSe in long-term stability and other active layer systems of PSCs is confirmed. Therefore, this work demonstrates that few-layered β-InSe has bright prospects in photovoltaic devices.

Theoretical insight on PTB7:PC71BM, PTB7-th:PC71BM and Si-PCPDTBT:PC71BM interactions governing blend nanoscale morphology for efficient solar cells

The nanoscale morphology of solution processed bulk heterojunctions is governed by miscibility of donor and acceptor in the selected solvent and drying of the layer during processing. Ternary blends are of great interest for high efficiency polymer solar cells, but prediction of their morphology is highly complex. Here we perform atomistic simulations to study the miscibility of three different polymers of interest for ternary organic photovoltaics (the small band gap polymers PTB7 and PTB7-th, and the sensitizer Si-PCPDTBT) with the fullerene acceptor PC71BM. The free energy of mixing of fullerenes with polymers is calculated as a function of the relative concentration. The blend density is also varied to simulate out-of-equilibrium conditions occurring during layer processing. By analyzing the results within the Flory–Huggins theory we find that, for a specific range of fullerene weight ratios and densely packed blends the sensitizer is most likely located in the host polymer phase due to its low miscibility with the fullerene. This configuration is the preferred one for the solar cell in order to deactivate hole traps typically formed in the binary blends and reduce recombination. Notably, we find that these results can be different qualitatively at lower density and in out-of-equilibrium blends. This work shows that weight ratios and density can be in principle chosen to select specific morphologies in ternary organic blends.

Room temperature and non-halogenated solvent processed terpolymers for high-efficient polymer solar cells

Most of polymer solar cells (PSCs) are currently processed using halogenated solvents and require high temperature manufacturing. However, the realization of non-halogenated environmental-friendly solvents processing and room temperature treatment are the basis for future commercialization of batteries. In this work, two terpolymers PffBT4T-4T2FC-9/1 and PffBT4T-4T2FC-4/1 were synthesized by introducing a self-assembly third unit, bis(2-hexyldecyl)5,5‴-dibromo-3″,4′-difluoro-[2,2’:5′,2’’:5″,2‴-quaterthiophene]-3,3‴-dicarboxylate (4T2FC) into the poly [(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di (2-octyldodecyl)-2,2’; 5′,2’’; 5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) polymer matrix via random copolymerization. The obtained terpolymers have relatively weaker self-aggregation properties and enable the spin-coating process at room temperature compared with the pristine copolymer PffBT4T-2OD. More importantly, the ester group of the 4T2FC unit can improve the solubility of the conjugated polymers in halogen-free solvent. Ultimately, a superior power conversion efficiency (PCE) of 9.11% was obtained from the optoelectronic device based on PffBT4T-4T2FC-9/1, which is one of the highest values of PSCs based on fullerene system treated with non-halogenated solvents at room temperature. These results demonstrate that these new terpolymers with ester group are promising candidates for high performance environmental-friendly solvent processed solar cells.