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All‐polymer solar cells (all‐PSCs), using polymerized non‐fullerene acceptors (PNFAs), have shown promise in improving device stabilities compared to small‐molecular acceptor‐based PSCs. However, low mixing entropy between polymer donors (PDs) and PNFAs hampers the development of optimized blend morphology. Herein, this study develops efficient conjugated polymers that serve as interfacial compatibilizers between host PD and PNFA. Ternary all‐polymer blends containing the compatibilizer demonstrate improved blend morphology with strengthened interfaces, resulting in better photovoltaic properties and thermal/mechanical stabilities. In detail, the power conversion efficiency (PCE) increases from 15.4 to 17.1% upon the addition of the compatibilizer. Moreover, the devices based on the ternary blend enable good thermal stability, retaining 90% of the initial PCE after 96 h at 125 °C. Additionally, the mechanical properties are improved; the cohesive fracture energy (Gc) of 2.6 J m−2 and crack onset strain (COS) of 20.4% of the ternary blend outperform those of the binary blend (Gc = 1.1 J m−2 and COS = 16.5%). Resultingly, the stretchable PSCs based on the ternary blend exhibit an excellent PCE of 13.7% and stretchability with a strain at PCE80% of 35%. [ABSTRACT FROM AUTHOR]

All‐polymer solar cells (all‐PSCs) have promising potential for industrial production due to their superior stability. Recently, the widespread application of the polymerized small molecule acceptor (PSMA) has led to a surge in the efficiency of all‐PSCs. However, the high efficiencies of these devices generally rely on the use of the highly volatile solvent, chloroform (CF). Furthermore, the molecular weights of PSMA are lower than polymer donors, yet their crystallinity is weaker than typical small molecules, making most PSMA‐based all‐PSCs suffer from low electron mobility. To improve device performance and facilitate large scale production of all‐PSCs, it is necessary to enhance electron mobility and avoid the use of CF. This paper investigates the use of sequential processing (SqP) for active layer preparation using toluene as the solvent to address these issues. This work reports 18.1% efficient all‐PSC devices, which is the highest efficiency of all‐PSCs prepared using non‐halogen solvents. This work systematically compares the conventional blend‐casting method with the SqP method using PM6 as the donor and PY‐V‐γ and PJ1‐γ as the acceptors, and compares the performance of binary and ternary blends in both methods. Finally, this work measures the device stability and finds that SqP can significantly improve the photostability of the device. [ABSTRACT FROM AUTHOR]

The realization of high‐efficiency organic solar cells (OSCs) from renewable sources will bring a real green energy technology. Benzo[1,2‐b:4,5‐b′]difuran (BDF) is such a building block for photovoltaic polymers as it can be built from furfural, which is available from trees and vegetables. However, the device performance of BDF‐based polymers is limited by aggregation properties and unfavorable active layer morphology. Herein, two new BDF‐based wide bandgap‐conjugated polymers, PFCT‐2F and PFCT‐2Cl, are developed by copolymerizing the fluorinated or chlorinated BDF units with the 3‐cyanothiophene unit for use as electron donors in OSCs. Benefitting from the more rotatable nature of the side‐chain thiophene rings on the BDF unit, PFCT‐2Cl exhibits more adjustable aggregation, higher π–π stacking ordering, and appropriate miscibility with the electron acceptor. As a result, a high power conversion efficiency (PCE) of 17.2% is offered by PFCT‐2Cl, which is nearly two times higher than that of PFCT‐2F (8.9%). A more remarkable PCE up to 17.5% is further achieved by PFCT‐2Cl in a ternary OSC, which is the new efficiency record for BDF‐based polymers. This success proves the critical role of aggregation control in BDF‐based polymers and the bright future for constructing high‐performance OSCs from bio‐renewable sources. [ABSTRACT FROM AUTHOR]

The realization of high‐efficiency organic solar cells (OSCs) from renewable sources will bring a real green energy technology. Benzo[1,2‐b:4,5‐b′]difuran (BDF) is such a building block for photovoltaic polymers as it can be built from furfural, which is available from trees and vegetables. However, the device performance of BDF‐based polymers is limited by aggregation properties and unfavorable active layer morphology. Herein, two new BDF‐based wide bandgap‐conjugated polymers, PFCT‐2F and PFCT‐2Cl, are developed by copolymerizing the fluorinated or chlorinated BDF units with the 3‐cyanothiophene unit for use as electron donors in OSCs. Benefitting from the more rotatable nature of the side‐chain thiophene rings on the BDF unit, PFCT‐2Cl exhibits more adjustable aggregation, higher π–π stacking ordering, and appropriate miscibility with the electron acceptor. As a result, a high power conversion efficiency (PCE) of 17.2% is offered by PFCT‐2Cl, which is nearly two times higher than that of PFCT‐2F (8.9%). A more remarkable PCE up to 17.5% is further achieved by PFCT‐2Cl in a ternary OSC, which is the new efficiency record for BDF‐based polymers. This success proves the critical role of aggregation control in BDF‐based polymers and the bright future for constructing high‐performance OSCs from bio‐renewable sources. [ABSTRACT FROM AUTHOR]

Hole transport materials (HTMs) play essential roles in achieving high photovoltaic performance and long‐term stability in the n–i–p structure of perovskite solar cell (PSC) devices. Recently, dopant‐free polymeric materials as HTMs in PSCs have attracted considerable attention owing to high carrier mobility and excellent hydrophobicity. However, achieving similar efficiencies to those of doped small molecule HTMs such as Spiro‐OMeTAD is a big challenge. Herein, a thienothiophene π‐bridge is selected as a stabilizer and energy level regulator incorporated into a donor–acceptor‐type HTM to synthesize a new polymer, Nap‐SiBTA. The incorporation of the thienothiophene group improves the thermal stability and favors the high planarity and face‐on orientation, promoting high charge carrier mobility and tunable optical band gap. Finally, the dopant‐free polymer Nap‐SiBTA‐based PSC achieves an excellent power conversion efficiency (PCE) of 23.07% with a high fill factor of 80.85%. To the best of the authors' knowledge, this is one of the best efficiencies in dopant‐free HTM PSCs. Moreover, the unencapsulated device retains 93% of its initial PCE after 1000 h owing to the excellent hydrophobicity of Nap‐SiBTA. This work provides a general and practical method to design dopant‐free HTMs for the high efficiency and long‐term stability of PSCs. [ABSTRACT FROM AUTHOR]

Following the 2nd release of the "Emerging PV reports," the best achievements in the performance of emerging photovoltaic devices in diverse emerging photovoltaic research subjects are summarized, as reported in peer‐reviewed articles in academic journals since August 2021. Updated graphs, tables, and analyses are provided with several performance parameters, e.g., power conversion efficiency, open‐circuit voltage, short‐circuit current density, fill factor, light utilization efficiency, and stability test energy yield. These parameters are presented as a function of the photovoltaic bandgap energy and the average visible transmittance for each technology and application, and are put into perspective using, e.g., the detailed balance efficiency limit. The 3rd installment of the "Emerging PV reports" extends the scope toward triple junction solar cells. [ABSTRACT FROM AUTHOR]

The emerging solution‐processed solar cells have attracted worldwide effort in the last decade. Developing efficient, stable, and cost‐effective solar cells is strongly desirable in countering the growing global warming. Nevertheless, the photovoltaic performance and stability of hybrid solar cells based on low‐cost polythiophenes are far from satisfactory, due to their high‐lying energy levels and excessive aggregation. Herein, it is shown that brominated polythiophene (P3HT‐Br), prepared via a facile two‐step approach can effectively facilitate charge transport and suppress recombination in quantum dot (QD)/organic heterojunctions. Accordingly, the power conversion efficiency of the optimized hybrid polythiophene/QD cell is boosted from 8.7% to 11% (a 26% increase) with markedly reduced energy loss. More strikingly, the device achieves record‐high thermal stability with a lifetime of over 400 h maintaining 80% of the initial performance. Both device efficiency and stability are the best reported for polythiophene/QD hybrid solar cells. Moving forward, brominated polythiophenes hold great application in perovskite solar cells with significantly improved performance and offer new opportunities for other emerging solar cells. [ABSTRACT FROM AUTHOR]

Polythiophenes (PTs) have attracted considerable interest for application in organic solar cells (OSCs) owing to their simple molecular structures and low‐cost synthesis. However, the power conversion efficiencies (PCEs) of PT‐based OSCs are lower than those of state‐of‐the‐art OSCs. Herein, the development of two sequentially fluorinated PT donors (PT‐2F and PT‐4F) is reported for realizing highly efficient OSCs. PT‐2F and PT‐4F are designed to contain two and four fluorine atoms, respectively, per repeating unit to decrease their highest occupied molecular orbital energy levels and increase the open‐circuit voltages of the OSCs. Importantly, the PT‐4F polymers exhibit high backbone rigidity and the desired temperature‐dependent aggregation behavior, affording well‐developed crystalline structures in thin films for efficient charge transport. These beneficial features promote the construction of an optimal blend morphology of PT‐4F:small‐molecule acceptor with a suitable energy offset and low energetic disorder. Thus, the PT‐4F‐based binary and ternary OSCs achieve high PCEs of 15.6% and 16.4%, respectively. [ABSTRACT FROM AUTHOR]

Efficient organic solar cells (OSCs) equipped with thick‐film active layers and high flexibility are of great significance for industrial preparation and practical applications. Herein, a ternary strategy coupled with a functional additive is employed to obtain efficient thick‐film flexible OSCs. A novel polymer donor PBB1‐F with good planarity is synthesized as a third component to optimize photon capture and molecular stacking. Meanwhile, a high dielectric constant polyarene ether (PAE) functional additive with strong adhesion not only greatly improves exciton dissociation efficiency, but also acts as locking cage‐like for effective enhancement of the mechanical stability of active layer. As a result, the PM6:PBB1‐F:Y6‐BO‐4Cl and PM6:PBB1‐F:BTP‐eC9 based ternary OSCs with PAE exhibit an efficiency of 17.91% and 18.51% under rigid thin‐film state, and perform better under thick‐film state of rigid (16.40% and 16.84%) and flexible (14.78% and 14.95%). Under the protection of the polymers, tight entanglement and cage‐like PAE adhesion, the elongation at break of the active layer increases by more than fourfold (27.3%), and gives a super flexible thick‐film OSCs that maintains more than 90% performance after 1000 bending cycles with a diameter of 10 mm. Overall, this work provides a new feasible scheme to effectively solve thickness sensitivity and flexibility issues in the context organic photovoltaic applications. [ABSTRACT FROM AUTHOR]

Solar photovoltaics (PV) offer viable and sustainable solutions to satisfy the growing energy demand and to meet the pressing climate targets. The deployment of conventional PV technologies is one of the major contributors of the ongoing energy transition in electricity power sector. However, the diversity of PV paradigms can open different opportunities for supplying modern systems in a wide range of terrestrial, marine, and aerospace applications. Such ubiquitous and versatile applications necessitate the development of PV technologies with customized design capabilities. This involves multifunctional characteristics such as aesthetic appearance, visual comfort, and heat insulation. To enable on‐demand adaptation to the requirements of distributed applications, tunable solar cells (SC) feature exceptional degrees of freedom in the manipulation of their intrinsic properties via adjusted materials engineering. The pertinent tuning abilities include but are not limited to bandgap energy, transparency, color, and thermal management. In this review, the main principles of different tuning approaches are specified and an overview of relevant concepts of tunable SC technologies is presented. Then, the recent integrations of cutting‐edge tunable PV adapted to versatile applications are systematically summarized. In addition, current challenges and insightful perspectives into potential future opportunities for omnipresent tunable PV are discussed. [ABSTRACT FROM AUTHOR]

Molecular aggregation and crystallization during film coating play a crucial role in the realization of high‐performing organic photovoltaics. Strong intermolecular interactions and high solid‐state crystallinity are beneficial for charge transport. However, fast crystallization during thin‐film drying often limits the formation of the finely phase‐separated morphology required for efficient charge generation. Herein, the authors show that twisted acceptor‐donor‐acceptor (A‐D‐A) type compounds, containing an indacenodithiophene (IDT) electron‐rich core and two naphthalenediimide (NDI) electron‐poor units, leads to formation of mostly amorphous phases in the as‐cast film, which can be readily converted into more crystalline domains by means of thermal annealing. This design strategy solves the aforementioned conundrum, leading to an optimal morphology in terms of reduced donor/acceptor domain‐separation sizes (ca. 13 nm) and increased packing order. Solar cells based on these acceptors with a PBDB‐T polymer donor show a power conversion efficiency over 10% and stable morphology, which results from the combined properties of desirable excited‐state dynamics, high charge mobility, and optimal aggregation/crystallization characteristics. These results demonstrate that the twisted A‐D‐A motif featuring thermally‐induced crystallization behavior is indeed a promising alternative design approach toward more morphologically robust materials for efficient organic photovoltaics. [ABSTRACT FROM AUTHOR]

The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have increased rapidly owing to the development of non‐fullerene acceptors (NFAs). However, the development of polymer donors lags behind significantly. Currently, the polymer donors are dominated by a handful of thiophene‐substituted benzo[1,2‐b:4,5‐b']dithiophene (BDTT) polymers, which suffer from lengthy synthesis and high production cost. Compared with BDTT‐based polymers, oligothiophene‐based donor‐acceptor polymers feature much easier synthesis, which were the prevailing polymer donors in fullerene‐based OSCs, but almost disappeared in non‐fullerene OSCs. Herein, two oligothiophene‐based donor‐acceptor polymers (PTTz‐3HD and PTTz‐4HD) are reported to re‐evaluate this kind of polymer in non‐fullerene OSCs. Benefiting from the exquisite alkyl chain design, the polymer PTTz‐3HD exhibits more planar conformation, stronger aggregation, and higher crystallinity, which in turn contributes to the formation of an optimal active layer morphology when blended with NFA. As a result, a PCE of 16.1% and 16.7% is achieved by PTTz‐3HD in binary and ternary OSCs, respectively. Of particular note, the product of short‐circuit current density and fill factor of PTTz‐3HD is fully comparable to those of BDTT‐based polymers. These results suggest the renaissance of oligothiophene‐based donor‐acceptor polymers in OSCs and demonstrate a promising avenue to access high‐efficiency OSCs from low‐cost materials. [ABSTRACT FROM AUTHOR]

A novel non‐volatile additive, fluorinated bis(perfluorophenyl)pimelate (BF7), is demonstrated to effectively improve both the efficiency and thermal stability of a highly efficient organic solar cell (OSC), comprising fluorinated Y6 as the small‐molecule acceptor and PM6 as the polymer donor. Processed with optimized 0.5 wt% BF7 in solution, the PM6:Y6:BF7 device achieves an elevated power conversion efficiency (PCE) of 17.01%, compared to 15.16% of that processed without BF7. Moreover, the BF7‐elevated PCE can sustain 95% of the best PCE over 100 °C annealing for 72 h. Grazing incidence X‐ray scattering and differential scanning calorimetry results consistently indicate that BF7 in the PM6:Y6:BF7 device interacts preferentially with Y6, resulting in improved fractal‐like network structures of the active layer with optimized size and orientation of Y6 nano‐crystallites and elevated thermal stability. Molecular simulation also supports that the observed structure and thermal stability is associated with the F–π noncovalent supramolecular interactions between the perfluorophenyl moieties of BF7 and difluorophenyl‐based FIC‐end‐groups of Y6. Similar bifunctional BF7 effects are also observed in the well‐known PM6:IT‐4F system, suggesting that adding BF7 for concomitantly improved PCE and thermal stability might extend generally to OSCs that feature small molecule acceptors of difluorophenyl end‐groups. [ABSTRACT FROM AUTHOR]

Tuning the aggregation and crystalline properties of polymers is critical for realizing all‐polymer solar cells (all‐PSCs) with optimal blend morphology and high power conversion efficiency (PCE). In this study, a series of polymerized small‐molecule acceptors (PSMAs) is developed to investigate important relationships among their crystalline/aggregation properties, the blend morphology, and the device performance of the resulting all‐PSCs. A series of PSMAs (regiorandom (RRd)‐C12, RRd‐C20, RRd‐C24, regioregular (RRg)‐C20, and RRg‐C24) with simultaneously‐engineered i) side chain lengths of C12, C20, and C24, and ii) backbone regioregularities of RRd and RRg are synthesized to regulate their crystalline/aggregation properties. As a result, the highest PCE of 15.12% is obtained with all‐PSCs based on RRg‐C20 PSMA having regioregular backbone and optimal side chain length, attributed to high PSMA crystallinity and electron mobility as well as optimal blend morphology with a polymer donor. Thus, this study demonstrates the importance of simultaneous engineering of the backbone regioregularity and side‐chain structures of PSMAs to enhance electron mobility, optimize blend morphology and, thus, achieve highly efficient all‐PSCs. [ABSTRACT FROM AUTHOR]

Fluorination of the donor and/or acceptor blocks of photoactive semiconducting polymers is a leading strategy to enhance organic solar cell (OSC) performance. Here, the effects are investigated in OSCs using fluorine‐free (TPD‐3) and fluorinated (TPD‐3F) donor polymers, paired with the nonfullerene acceptor Y6. Interestingly and unexpectedly, fluorination negatively affects performance, and fluorine‐free TPD‐3:Y6 OSCs exhibit a far higher power conversion efficiency (PCE = 14.5%) than in the fluorine‐containing TPD‐3F:Y6 blends (PCE = 11.5%). Transmission electron microscopy (TEM) analysis indicates that the TPD‐3F:Y6 blends have larger phase domain sizes than TPD‐3:Y6, which reduces exciton dissociation efficiency to 81% for TPD‐3F:Y6 versus 93% for TPD‐3:Y6. Additionally, grazing incidence wide‐angle X‐ray scattering (GIWAXS) reveals that the TPD‐3F:Y6 blends are less textured than those of TPD‐3:Y6, while space‐charge limited currents reveal lower and unbalanced hole/electron mobility in TPD‐3F:Y6 versus TPD‐3:Y6 blends. Charge recombination dynamic, transient absorption, and donor–acceptor miscibility assays additionally support this picture. Furthermore, conventional architecture TPD‐3:Y6 OSCs deliver a PCE of 15.2%, among the highest to date for halogen‐free polymer donor OSCs. Finally, a large‐area (20.4 cm2) TPD‐3:Y6 blend module exhibits an outstanding PCE of 9.31%, one of the highest to date for modules of area >20 cm2. [ABSTRACT FROM AUTHOR]

Side‐chain modifications of non‐fullerene acceptors (NFAs) are essential for harvesting their full potential in organic solar cells (OSC). Here, an effective alkyl‐chain‐branching approach of the Y‐series NFAs flanking meta‐substituted phenyl side groups at the outer positions is demonstrated. Compared to BTP‐4F‐PC6 with linear m‐hexylphenyl chains, two new acceptors named BTP‐4F‐P2EH and BTP‐4F‐P3EH are developed with bulkier alkyl chains branched at the β and γ positions, respectively. These branched chains result in altered molecular packing of the NFAs and afford higher open‐circuit voltage of the devices. Despite the blue‐shifted absorption of the branched‐chain NFAs, their blends with PBDB‐T‐2F enable improved short‐circuit current density for the corresponding devices owing to the more suitable phase separation and better exciton dissociation. Consequently, the OSCs based on BTP‐4F‐P2EH and BTP‐4F‐P3EH yield enhanced device performance of 18.22% and 17.57%, respectively, outperforming the BTP‐4F‐PC6‐based ones (17.22%). These results highlight that the side‐chain branching design of NFAs has great potential in optimizing molecular properties and promoting photovoltaic performance. [ABSTRACT FROM AUTHOR]

The molecular ordering and pre‐aggregation of photovoltaic materials in solution can significantly affect the nanoscale morphology in solid photoactive layers, and play a vital role in determining the power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, a cold‐aging strategy is reported to mediate the pre‐aggregation of PM6 polymer in solution through a disorder‐order transition, which leads to dense and fine PM6 aggregates with enhanced π−π stacking in its blend thin films with either fused‐ring and non‐fused‐ring non‐fullerene acceptors (NFAs) including Y6‐BO, N3, IT‐4F, and PTIC. The fine aggregates of PM6 and slightly enlarged NFA domains improve the continuous networks with enhanced and balanced charge mobility. The resulting OSCs all demonstrate enhanced PCEs compared to their counterparts without any cold‐aging treatments, with PM6:Y6‐BO OSC being most effective from 16.6% to 17.7%, demonstrating the universality of this approach. This can be further optimized upon casting of the cold‐aging solution with the presence of solvent vapor, resulting in a champion PCE of 18.0% for PM6:Y6‐BO OSC, which is the highest PCE of this OSC reported in the literature. This work provides a rational guide for optimizing non‐fullerene OSCs via aggregation control before and during the solution casting process. [ABSTRACT FROM AUTHOR]

The power conversion efficiency of organic solar cell (OSC) devices has surpassed 18% rapidly. In order to further promote OSC development, it is necessary to understand the packing information at the atomic level to help develop acceptor systems with superior performance. The packing arrangements and intermolecular interactions of these acceptors in the solid state, observed by single crystal X‐ray crystallography, are often used to design materials with expected physicochemical properties. In this review, the chemical structures of acceptors revealed by single crystal X‐ray crystallography are summarized, and the relationship between structural design, packing arrangement, and device properties is discussed. In addition, the concept of "3D network packing" in acceptor systems is proposed, which offers better charge transfer properties in reported chlorinated, fluorinated, brominated, and trifluoromethylated systems, an understanding of 3D network transport also provides guidance in high‐performance materials design. Finally, some current issues related to single crystal studies in OSCs are discussed, with an emphasis on the significance of developing acceptors by understanding and adjusting the aggregation states and intermolecular interactions of materials by single crystal analysis. [ABSTRACT FROM AUTHOR]

Herein the morphology and exciton/charge carrier dynamics in bulk heterojunctions (BHJs) of the donor polymer PTQ10 and molecular acceptor IDIC are investigated. PTQ10:IDIC BHJs are shown to be particularly promising for low cost organic solar cells (OSCs). It is found that both PTQ10 and IDIC show remarkably high crystallinity in optimized BHJs, with GIWAXS data indicating pi‐pi stacking coherence lengths of up to 8 nm. Exciton‐exciton annihilation studies indicate long exciton diffusion lengths for both neat materials (19 nm for PTQ10 and 9.5 nm for IDIC), enabling efficient exciton separation with half lives of 1 and 3 ps, despite the high degree of phase segregation in this blend. Transient absorption data indicate exciton separation leads to the formation of two spectrally distinct species, assigned to interfacial charge transfer (CT) states and separated charges. CT state decay is correlated with the appearance of additional separate charges, indicating relatively efficient CT state dissociation, attributed to the high crystallinity of this blend. The results emphasize the potential for high material crystallinity to enhance charge separation and collection in OSCs, but also that long exciton diffusion lengths are likely to be essential for efficient exciton separation in such high crystallinity devices. [ABSTRACT FROM AUTHOR]

Abstract: Donor–acceptor (D‐A) type π‐conjugated copolymers with crystalline behavior have been extensively investigated as donor semiconductors in organic photovoltaics (OPVs). On the other hand, the development of high‐performance amorphous donor materials is still behind. The amorphous donor copolymer DTS‐C0(F2) consisting of dithieno[3,2‐b:2′,3′‐d]silole (DTS) donor unit and the recently developed fluorine‐substituted naphtho[2,3‐c]thiophene‐4,9‐dione (C0(F2)) acceptor unit shows moderate photovoltaic performance upon blending with PC71BM. In this work, to enhance the hole‐transporting characteristics, a 3‐hexylthiophene (HT) spacer unit is integrated into the conjugated backbone, resulting in a new amorphous copolymer DTS‐HT‐C0(F2). The strong electron‐accepting nature of C0(F2) allows the introduction of the HT spacer without affecting the frontier orbital energies and thus the D‐A character. Without using solvent additives and thermal annealing, OPVs based on DTS‐HT‐C0(F2) and [6,6]‐phenyl‐C71‐butyric acid methyl ester PC71BM show an improved power conversion efficiency of 9.12%. Investigation of the device physics unambiguously reveals that the hole mobility of the copolymer in the blend is increased by an order of magnitude by the introduction of HT, while keeping an amorphous film nature, leading to higher short‐circuit current density and fill factor. These results demonstrate the realization of high‐performance OPVs based on amorphous active layers. [ABSTRACT FROM AUTHOR]

'Nonfullerene' acceptors are proving effective in bulk heterojunction (BHJ) solar cells when paired with selected polymer donors. However, the principles that guide the selection of adequate polymer donors for high-efficiency BHJ solar cells with nonfullerene acceptors remain a matter of some debate and, while polymer main-chain substitutions may have a direct influence on the donor-acceptor interplay, those effects should be examined and correlated with BHJ device performance patterns. This report examines a set of wide-bandgap polymer donor analogues composed of benzo[1,2- b:4,5- b′]dithiophene (BDT), and thienyl ([2H]T) or 3,4-difluorothiophene ([2F]T) motifs, and their BHJ device performance pattern with the nonfullerene acceptor 'ITIC'. Studies show that the fluorine- and ring-substituted derivative PBDT(T)[2F]T largely outperforms its other two polymer donor counterparts, reaching power conversion efficiencies as high as 9.8%. Combining several characterization techniques, the gradual device performance improvements observed on swapping PBDT[2H]T for PBDT[2F]T, and then for PBDT(T)[2F]T, are found to result from (i) notably improved charge generation and collection efficiencies (estimated as ≈60%, 80%, and 90%, respectively), and (ii) reduced geminate recombination (being suppressed from ≈30%, 25% to 10%) and bimolecular recombination (inferred from recombination rate constant comparisons). These examinations will have broader implications for further studies on the optimization of BHJ solar cell efficiencies with polymer donors and a wider range of nonfullerene acceptors. [ABSTRACT FROM AUTHOR]

The field of conjugated polymers has expanded in the last years considerably and impressive performance, both in field effect transistors and photovoltaic devices has been achieved. After the initial emphasis on improving the performance, more emphasis is recently given to fundamental studies on structure formation. Therefore, this review concentrates on systematic correlation studies of structure formation in solution, in bulk and thin films as well as in photovoltaic blends of donor-type π-conjugated polymers. The main focus is on the correlation of structure, morphology and molecular chain orientation as a function of macromolecular properties such as molecular weight, dispersity, non-covalent intramolecular and intermolecular interactions, solvent interactions and innovative processing techniques. The tools applied for elucidating fundamental information of structure formation and orientation mainly consist of optical spectroscopy and scattering techniques (SAXS/WAXS/GIWAXS). Since the field of conjugated polymers is very vast in terms of chemical structural diversity, only selected examples of donor polymers are covered here and the emerging class of n-type conjugated polymers are not included. The focus is not on the structural variation or their performance in solar cells or transistors in terms of record efficiencies, but on the systematic studies leading to a structure-property correlation in donor polymers. [ABSTRACT FROM AUTHOR]

All-polymer solar cells (all-PSCs) utilizing p-type polymers as electron-donors and n -typepolymers as electron-acceptors have attracted a great deal of attention, and their efficiencies have been improved considerably. Here, five polymer donors with different molecular orientations are synthesized by random copolymerization of 5-fluoro-2,1,3-benzothiadiazole with different relative amounts of 2,2′-bithiophene (2T) and dithieno[3,2- b;2′,3′- d]thiophene (DTT). Solar cells are prepared by blending the polymer donors with a naphthalene diimide-based polymer acceptor (PNDI) or a [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) acceptor and their morphologies and crystallinity as well as optoelectronic, charge-transport and photovoltaic properties are studied. Interestingly, charge generation in the solar cells is found to show higher dependence on the crystal orientation of the donor polymer for the PNDI-based all-PSCs than for the conventional PC71BM-based PSCs. As the population of face-on-oriented crystallites of the donor increased in PNDI-based PSC, the short-circuit current density ( JSC) and external quantum efficiency of the devices are found to significantly improve. Consequently, device efficiency was enhanced of all-PSC from 3.11% to 6.01%. The study reveals that producing the same crystal orientation between the polymer donor and acceptor (face-on/face-on) is important in all-PSCs because they provide efficient charge transfer at the donor/acceptor interface. [ABSTRACT FROM AUTHOR]

Highly efficient, indium tin oxide (ITO)‐free and flexible organic photovoltaic cells are demonstrated with 10.4% power conversion efficiency (PCE) through the innovative integration of ultrathin metal film electrode, conductive fullerene interfacial layer, and efficient active blend into a microcavity‐embedded device. In addition, a high PCE of 7.21% is achieved for the upsized devices with an active area of 1 cm2. [ABSTRACT FROM AUTHOR]