Showing papers on "Polymer solar cell published in 2022"

Realizing 19.05% Efficiency Polymer Solar Cells by Progressively Improving Charge Extraction and Suppressing Charge Recombination

Abstract: Improving charge extraction and suppressing charge recombination are critically important to minimize the loss of absorbed photons and improve the device performance of polymer solar cells (PSCs). In this work, highly efficient PSCs are demonstrated by progressively improving the charge extraction and suppressing the charge recombination through the combination of side‐chain engineering of new nonfullerene acceptors (NFAs), adopting ternary blends, and introducing volatilizable solid additives. The 2D side chains on BTP‐Th induce a certain steric hindrance for molecular packing and phase separation, which is mitigated by fluorination of side chains on BTP‐FTh. Moreover, by introducing two highly crystalline molecules as the second acceptor and volatilizable solid additive, respectively, into the BTP‐FTh‐based host blend, the molecular crystallinity is significantly improved and the blend morphology is finely optimized. As expected, enhanced charge extraction and suppressed charge recombination are progressively realized, contributing to the largely improved fill factor (FF) of the resultant devices. Accompanied by the enhanced open‐circuit voltage (Voc) and short‐circuit current density (Jsc), a record high power conversion efficiency (PCE) of 19.05% is realized finally.

A Vinylene‐Linker‐Based Polymer Acceptor Featuring a Coplanar and Rigid Molecular Conformation Enables High‐Performance All‐Polymer Solar Cells with Over 17% Efficiency

Abstract: State‐of‐art Y‐series polymer acceptors are typically based on a mono‐thiophene linker, which can cause some twisted molecular conformations and thus limit the performance of all‐polymer solar cells (all‐PSCs). Here, a high‐performance polymer acceptor based on vinylene linkers is reported, which leads to surprising changes in the polymers’ molecular conformations, optoelectronic properties, and enhanced photovoltaic performance. It is found that the polymer acceptors based on thiophene or bithiophene linkers (PY‐T‐γ and PY‐2T‐γ) display significant molecular twisting between end‐groups and linker units, while the vinylene‐based polymer (PY‐V‐γ) exhibits a more coplanar and rigid molecular conformation. As a result, PY‐V‐γ demonstrates a better conjugation and tighter interchain stacking, which results in higher mobility and a reduced energetic disorder. Furthermore, detailed morphology investigations reveal that the PY‐V‐γ‐based blend exhibits high domain purity and thus a better fill factor in its all‐PSCs. With these, a higher efficiency of 17.1% is achieved in PY‐V‐γ‐based all‐PSCs, which is the highest efficiency reported for binary all‐PSCs to date. This work demonstrates that the vinylene‐linker is a superior unit to build polymer acceptors with more coplanar and rigid chain conformation, which is beneficial for polymer aggregation and efficient all‐PSCs.

Polymerized Small Molecular Acceptor with Branched Side Chains for All Polymer Solar Cells with Efficiency over 16.7%

Abstract: The power conversion efficiencies (PCEs) of small molecule acceptor (SMA)‐based organic solar cells have already exceeded 18%. However, the development of polymer acceptors still lags far behind their SMA counterparts mainly due to the lack of efficient polymer acceptors. Herein, a series of polymer acceptors named PY‐X (with X being the branched alkyl chain) are designed and synthesized by employing the same central core with the SMA L8‐BO but with different branched alkyl chains on the pyrrole motif. It is found that the molecular packing of SMA‐HD featuring 2‐hexyldecyl side chain used in the synthesis of PY‐HD is similar to L8‐BO, in which the branched alkyl chains lead to condensed and high‐order molecular assembly in SMA‐HD molecules. When combined with PM6, PY‐HD‐based all polymer solar cell (all‐PSC) exhibits a high PCE of 16.41%, representing the highest efficiency for the binary all‐PSCs. Moreover, the side‐chain modification on the pyrrole site position further improves the performance of the all‐PSCs, and the PY‐DT‐based device delivers a new record high efficiency of 16.76% (certified as 16.3%). The work provides new insights for understanding the structure–property relationship of polymer acceptors and paves a feasible avenue to develop efficient conjugated polymer acceptors.

Achieving 15.81% and 15.29% efficiency of all-polymer solar cells based on layer-by-layer or bulk heterojunction structure

Abstract: Wide bandgap polymer donor PM6 and narrow bandgap polymer acceptor PY-IT were selected to construct all-polymer solar cells (all-PSCs) with layer-by-layer (LbL) or bulk heterojunction (BHJ) structure. The additive 1-chloronaphthalene...

Heteroheptacene-based acceptors with thieno[3,2-b]pyrrole yield high-performance polymer solar cells

Abstract: Abstract Rationally utilizing and developing synthetic units is of particular significance for the design of high-performance non-fullerene small-molecule acceptors (SMAs). Here, a thieno[3,2-b]pyrrole synthetic unit was employed to develop a set of SMAs (ThPy1, ThPy2, ThPy3 and ThPy4) by changing the number or the position of the pyrrole ring in the central core based on a standard SMA of IT-4Cl, compared to which the four thieno[3,2-b]pyrrole-based acceptors exhibit bathochromic absorption and upshifted frontier orbital energy level due to the strong electron-donating ability of pyrrole. As a result, the polymer solar cells (PSCs) of the four thieno[3,2-b]pyrrole-based acceptors yield higher open-circuit voltage and lower energy loss relative to those of the IT-4Cl-based device. What is more, the ThPy3-based device achieves a power conversion efficiency (PCE) (15.3%) and an outstanding fill factor (FF) (0.771) that are superior to the IT-4Cl-based device (PCE = 12.6%, FF = 0.758). The ThPy4-based device realizes the lowest energy loss and the smallest optical band gap, and the ternary PSC device based on PM6:BTP-eC9:ThPy4 exhibits a PCE of 18.43% and a FF of 0.802. Overall, this work sheds light on the great potential of thieno[3,2-b]pyrrole-based SMAs in realizing low energy loss and high PCE.

16.52% Efficiency All‐Polymer Solar Cells with High Tolerance of the Photoactive Layer Thickness

Abstract: All‐polymer solar cells (all‐PSCs) have drawn growing attention and achieved tremendous progress recently, but their power conversion efficiency (PCE) still lags behind small‐molecule‐acceptor (SMA)‐based PSCs due to the relative difficulty on morphology control of polymer photoactive blends. Here, low‐cost PTQ10 is introduced as a second polymer donor (a third component) into the PM6:PY‐IT blend to finely tune the energy‐level matching and microscopic morphology of the polymer blend photoactive layer. The addition of PTQ10 decreases the π–π stacking distance, and increases the π–π stacking coherence length and the ordered face‐on molecular packing orientation, which improves the charge separation and transport in the photoactive layer. Moreover, the deeper highest occupied molecular orbital energy level of the PTQ10 polymer donor than PM6 leads to higher open‐circuit voltage of the ternary all‐PSCs. As a result, a PCE of 16.52% is achieved for ternary all‐PSCs, which is one of the highest PCEs for all‐PSCs. In addition, the ternary devices exhibit a high tolerance of the photoactive layer thickness with high PCEs of 15.27% and 13.91% at photoactive layer thickness of ≈205 and ≈306 nm, respectively, which are the highest PCEs so far for all‐PSCs with a thick photoactive layer.

Fibrillization of Non‐Fullerene Acceptors Enables 19% Efficiency Pseudo‐Bulk Heterojunction Organic Solar Cells

Abstract: The structural order and aggregation of non‐fullerene acceptors (NFA) are critical toward light absorption, phase separation, and charge transport properties of their photovoltaic blends with electron donors, and determine the power conversion efficiency (PCE) of the corresponding organic solar cells (OSCs). In this work, the fibrillization of small molecular NFA L8‐BO with the assistance of fused‐ring solvent additive 1‐fluoronaphthalene (FN) to substantially improve device PCE is demonstrated. Molecular dynamics simulations show that FN attaches to the backbone of L8‐BO as the molecular bridge to enhance the intermolecular packing , inducing 1D self‐assembly of L8‐BO into fine fibrils with a compact polycrystal structure. The L8‐BO fibrils are incorporated into a pseudo‐bulk heterojunction (P‐BHJ) active layer with D18 as a donor, and show enhanced light absorption, charge transport, and collection properties, leading to enhanced PCE from 16.0% to an unprecedented 19.0% in the D18/L8‐BO binary P‐BHJ OSC, featuring a high fill factor of 80%. This work demonstrates a strategy for fibrillating NFAs toward the enhanced performance of OSCs.

Tuning Morphology of Active Layer by using a Wide Bandgap Oligomer‐Like Donor Enables Organic Solar Cells with Over 18% Efficiency

Abstract: A wide bandgap oligomer‐like donor CNS‐6‐8 is synthesized and incorporated into the host PM6:Y6:PC71BM system to tune the morphology of the active layer for better device performance. Due to the good miscibility of CNS‐6‐8 with both host donor (PM6) and acceptors (Y6 and PC71BM), an optimized morphology is achieved with the appropriate phase separation size and enhanced crystallinity, which ultimately leads to more efficient exciton dissociation, charge transport, and lower nonradiative energy loss. As a result, the quaternary device achieves an improved efficiency of 18.07%, with a simultaneously increased open circuit voltage of 0.868 V, fill factor of 78.8%, and the comparable short‐circuit current density of 26.43 mA cm−2. This work indicates that the favorable 3D interpenetrating network morphology of Y6 containing blend films can be optimized by introducing small amount of a specific molecule with high crystallinity, thus providing an effective strategy to achieve better photovoltaic performance for state‐of‐the‐art Y6 analogs‐based organic solar cells.

Achieving 17.5% efficiency of polymer solar cells via donor and acceptor layered optimization strategy

Abstract: Layer-by-layer polymer solar cells (LbL-PSCs) were prepared with PNTB6-Cl as donor and Y6 as acceptor by sequential spin-coating method. Two solvent additives DPE and DFB were individually incorporated into PNTB6-Cl...

A New alcohol‐soluble polymer PFN‐ID as cathode interlayer to optimize performance of conventional polymer solar cells by increasing electron mobility

Abstract: A new alcohol-soluble polymer PFN-ID is successfully synthesized by combining N,N-di(2-ethylhexyl)-6,6′-dibromoisoindigo and an amino-containing fluorene subunits, and applied to polymer solar cells (PSCs) with PTB7-Th:PC71BM as an active layer. The n-type backbone of the PFN-ID improves electron transfer performance and thus optimizes device performance. The PSCs with PFN-ID as cathode interfacial layers (CILs) have significantly improved compared to the device without the interface layer, especially the optimum power conversion efficiency (PCE) of PSCs reaches up to 9.24%, which is 1.62 times higher than that of devices without CILs. The I–V curves show that the introduction of the n-type backbone leads to a significant increase in the conductivity of PFN-ID compared to PFN. The UV photoelectron spectroscopy and Mott–Schottky curves further confirm that PFN-ID can decrease the work function of Al electrode, and increase its built-in potential, giving higher open-circuit voltage. The resulting conventional PSCs using PFN-ID as cathode interlayer achieve high photovoltaic performance, and the research results can provide a new strategy for the advancement of PSCs.

An efficient polymer acceptor <i>via</i> a random polymerization strategy enables all-polymer solar cells with efficiency exceeding 17%

Abstract: A series of polymer acceptors have been synthesized. The optical and electronic properties of the copolymers can be well-tuned via a random copolymerization strategy. The best-performing PY-82-based binary device produces a record-high efficiency of 17.15%.

Binary Blend All‐Polymer Solar Cells with a Record Efficiency of 17.41% Enabled by Programmed Fluorination Both on Donor and Acceptor Blocks

Abstract: Despite remarkable breakthrough made by virtue of “polymerized small‐molecule acceptor (PSMA)” strategy recently, the limited selection pool of high‐performance polymer acceptors and long‐standing challenge in morphology control impede their further developments. Herein, three PSMAs of PYDT‐2F, PYDT‐3F, and PYDT‐4F are developed by introducing different fluorine atoms on the end groups and/or bithiophene spacers to fine‐tune their optoelectronic properties for high‐performance PSMAs. The PSMAs exhibit narrow bandgap and energy levels that match well with PM6 donor. The fluorination promotes the crystallization of the polymer chain for enhanced electron mobility, which is further improved by following n‐doping with benzyl viologen additive. Moreover, the miscibility is also improved by introducing more fluorine atoms, which promotes the intermixing with PM6 donor. Among them, PYDT‐3F exhibits well‐balanced high crystallinity and miscibility with PM6 donor; thus, the layer‐by‐layer processed PM6/PYDT‐3F film obtains an optimal nanofibril morphology with submicron length and ≈23 nm width of fibrils, facilitating the charge separation and transport. The resulting PM6/PYDT‐3F devices realizes a record high power conversion efficiency (PCE) of 17.41% and fill factor of 77.01%, higher than the PM6/PYDT‐2F (PCE = 16.25%) and PM6/PYDT‐4F (PCE = 16.77%) devices.

High‐Performance Organic Solar Modules via Bilayer‐Merged‐Annealing Assisted Blade Coating

Abstract: Although encouraging progress is being made on spin‐coated prototype cells, organic solar cells (OSCs) still face significant challenges, yet to be explored, for upscaling the multi‐stacked photoactive layers in the construction of large‐area modules. Herein, high‐performance opaque and semitransparent organic solar modules are developed via a bilayer‐merged‐annealing (BMA)‐assisted blade‐coating strategy, achieving impressive efficiencies of 14.79% and 12.01% with respect to active area of 18.73 cm2, which represent the best organic solar minimodules so far. It is revealed that the BMA strategy effectively resolves the de‐wetting issues between polar charge transport layer solution and non‐polar bulk heterojunction blends, hence improving the film coverage, along with electronic and electric contacts of multi‐stacked photoactive layers. As result, organic solar modules coated under ambient conditions successfully retain the high‐efficiency of small‐area cells upon 312 times area scaling‐up. Overall, this work provides a facile and effective method to fabricate high‐performance organic solar modules under ambient conditions.

Nonhalogenated Dual‐Slot‐Die Processing Enables High‐Efficiency Organic Solar Cells

Abstract: Organic solar cells (OSCs) are promising candidates for next‐generation photovoltaic technologies, with their power conversion efficiencies (PCEs) reaching 19%. However, the typically used spin‐coating method, toxic halogenated processing solvents, and the conventional bulk‐heterojunction (BHJ), which causes excessive charge recombination, hamper the commercialization and further efficiency promotion of OSCs. Here, a simple but effective dual‐slot‐die sequential processing (DSDS) strategy is proposed to address the above issues by achieving a continuous solution supply, avoiding the solubility limit of the nonhalogen solvents, and creating a graded‐BHJ morphology. As a result, an excellent PCE of 17.07% is obtained with the device processed with o‐xylene in an open‐air environment with no post‐treatment required, while a PCE of over 14% is preserved in a wide range of active‐layer thickness. The unique film‐formation mechanism is further identified during the DSDS processing, which suggests the formation of the graded‐BHJ morphology by the mutual diffusion between the donor and acceptor and the subsequent progressive aggregation. The graded‐BHJ structure leads to improved charge transport, inhibited charge recombination, and thus an excellent PCE. Therefore, the newly developed DSDS approach can effectively contribute to the realm of high‐efficiency and eco‐friendly OSCs, which can also possibly be generalized to other organic photoelectric devices.

Toward Efficiency Limits of Crystalline Silicon Solar Cells: Recent Progress in High‐Efficiency Silicon Heterojunction Solar Cells

Abstract: Photovoltaic (PV) technology is ready to become one of the main energy sources of, and contributers to, carbon neutrality by the mid‐21st century. In 2020, a total of 135 GW of PV modules were produced. Crystalline silicon solar cells dominate the world's PV market due to high power conversion efficiency, high stability, and low cost. Silicon heterojunction (SHJ) solar cells are one of the promising technologies for next‐generation crystalline silicon solar cells. Compared to the commercialized homojunction silicon solar cells, SHJ solar cells have higher power conversion efficiency, lower temperature coefficient, and lower manufacturing temperatures. Recently, several new record efficiencies have been achieved. To meet the continued demand for high‐efficiency solar cells, expectations for large‐scale mass production of SHJ solar cells are rising. To approach the efficiency limit and industrialization of SHJ solar cells, serious attempts have been made, yielding higher short‐circuit current, open‐circuit voltage, and fill factor. In this article, these recent advancements are reviewed, which reveals the future roadmap for approaching the efficiency limit.

Simultaneously Achieving Highly Efficient and Stable Polymer:Non‐Fullerene Solar Cells Enabled By Molecular Structure Optimization and Surface Passivation

Abstract: Despite the tremendous efforts in developing non‐fullerene acceptor (NFA) for polymer solar cells (PSCs), only few researches are done on studying the NFA molecular structure dependent stability of PSCs, and long‐term stable PSCs are only reported for the cells with low efficiency. Herein, the authors compare the stability of inverted PM6:NFA solar cells using ITIC, IT‐4F, Y6, and N3 as the NFA, and a decay rate order of IT‐4F > Y6 ≈ N3 > ITIC is measured. Quantum chemical calculations reveal that fluorine substitution weakens the C═C bond and enhances the interaction between NFA and ZnO, whereas the β‐alkyl chains on the thiophene unit next to the C═C linker blocks the attacking of hydroxyl radicals onto the C═C bonds. Knowing this, the authors choose a bulky alkyl side chain containing molecule (named L8‐BO) as the acceptor, which shows slower photo bleaching and performance decay rates. A combination of ZnO surface passivation with phenylethanethiol (PET) yields a high efficiency of 17% and an estimated long T80 and Ts80 of 5140 and 6170 h, respectively. The results indicate functionalization of the β‐position of the thiophene unit is an effective way to improve device stability of the NFA.

Balancing the Molecular Aggregation and Vertical Phase Separation in the Polymer: Nonfullerene Blend Films Enables 13.09% Efficiency of Organic Solar Cells with Inkjet‐Printed Active Layer

Abstract: Drop‐on demand inkjet‐printing (IJP) is a deposition technique with promise in the context of fabricating large‐area organic solar cells (OSCs) because of its high material usage, direct‐pattern, and large‐area roll‐to‐roll printing compatibility. But its feature of drop‐to‐drop deposition during IJP makes the film's drying and phase separation process different from spin‐coating, and forms different nanophase separation and vertical phase separation morphology. In this work, the nanophase separation of the inkjet‐printed organic blend films is systematically studied at different substrate temperatures. The results reveal that increasing the substrate temperature can suppress excess molecules aggregation owing to the high drying speed, leading to improved exciton dissociation efficiency in the blend films. However, the quick drying process at high temperature also leads to a homogenous vertical phase separation, which is not ideal for charge collection. Instead of printing the mixture of donor and acceptor solution directly to form the bulk‐heterojunction structure, the polymer donor is printed on the top of the acceptor surface, a so‐called layer‐by‐layer inkjet printing (LBL‐IJP) process. By using this LBL‐IJP route, balanced nanoscale phase aggregation and gradient vertical phase separation morphology are achieved, which leads to a record power conversion efficiency of 13.09% for the OSCs with an inkjet‐printed active layer.

Quasiplanar Heterojunction All‐Polymer Solar Cells: A Dual Approach to Stability

Abstract: In addition to efficiency, stability is another key factor in developing organic solar cells. The quasiplanar heterojunction (Q‐PHJ) structure, combining two pure layers as major and tiny nanoscale bulk heterojunction (BHJ) at interface, demonstrates superior device stability compared with BHJ devices. In this contribution, the polymer donor, PBQx‐H‐TF, and configurationally defined polymeric acceptor, PBTIC‐γ‐TSe are synthesized and used to fabricate bilayer devices by orthogonal solvents, the corresponding Q‐PHJ all‐polymer solar cells (all‐PSCs) deliver reliable stability with high efficiency. An encouraging PCE of 15.77% is achieved, which is the highest one among Q‐PHJ all‐PSCs with real‐bilayer structure. There is a major improvement over the 13.91% PCE in the BHJ device, and the carrier transport performance is improved substantially following the reduction of recombination in the Q‐PHJ all‐PSCs. Benefiting from the bilayer morphology, the stability of Q‐PHJ all‐PSCs has been greatly enhanced over that of the BHJ devices. The charge recombination process is also more serious in the aging BHJ compared with the aging Q‐PHJ all‐PSCs. This work inspires the application of Q‐PHJ in the preparation of high‐efficient all‐PSCs, but also provides guidance on the improvement of device stability from a dual approach of material and device engineering aspects.