Yingzhi Jin

Nature Energy, Published online: 27 October 2022; doi:10.1038/s41560-022-01140-4

A unique conformation lock is formed in a polymer donor using an unconventional carbamate side chain. It gives wide band-gap polymer donors for application in organic solar cells. Devices incorporating these donors yield power conversion efficiencies up to 18.76 %.

Abstract

Side-chain engineering with heteroatoms is not only effective in tuning frontier molecular orbitals, but also possible for forming secondary bonds which can be utilized to planarize the molecular backbone, hence, improving the photon absorption as well as charge-transport abilities of polymer solar-cell (PSC) materials. Herein, two types of unconventional side chains, namely carboxylate and carbamate, containing various heteroatoms are introduced to the thiophene bridges in high performance benzodithiophene (BDT) based donor polymers to from the novel polymers PTzTz-C and PTzTz-N, respectively. In these polymers, non-covalent O⋅⋅⋅S and N⋅⋅⋅H interactions induce a high tendency to aggregation. In a ternary-blend PSC with PTzTz-N added to the high-performance D18 : BTP-eC9 blend, complimentary absorption and improved thin-film morphology were observed with a top power conversion efficiency of 18.76 %, which is an improvement of almost 5 % over the D18 : BTP-eC9 binary blends.

Functionalization of poly(3,4-ethylenedioxythiophene) (PEDOT) with ester-based side chains allows for solution processing and moderate electrical conductivity. Hydrolysis of these side chains leaves hydroxymethyl functional groups on the polymer, increases the relative amount of electroactive material, significantly increases electrical conductivity to greater than 1000 S cm⁻¹, and changes the transport mechanism from hopping-like to metal-like.

Abstract

Herein, a route to produce highly electrically conductive doped hydroxymethyl functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films, termed PEDOT(OH) with metal-like charge transport properties using a fully solution processable precursor polymer is reported. This is achieved via an ester-functionalized PEDOT derivative [PEDOT(EHE)] that is soluble in a range of solvents with excellent film-forming ability. PEDOT(EHE) demonstrates moderate electrical conductivities of 20–60 S cm⁻¹ and hopping-like (i.e., thermally activated) transport when doped with ferric tosylate (FeTos₃). Upon basic hydrolysis of PEDOT(EHE) films, the electrically insulative side chains are cleaved and washed from the polymer film, leaving a densified film of PEDOT(OH). These films, when optimally doped, reach electrical conductivities of ≈1200 S cm⁻¹ and demonstrate metal-like (i.e., thermally deactivated and band-like) transport properties and high stability at comparable doping levels.

Acceptor-acceptor type homopolymer PDTzTI-TEG bearing ethylene glycol side chains is synthesized and the doped PDTzTI-TEG exhibits n-type conductivity up to 34 S cm⁻¹ and power factor of 15.7 μW m⁻¹ K⁻². These values are far superior to those of analogous acceptor-donor type copolymers, indicating that PDTzTI-TEG is a promising material for organic thermoelectrics.

Abstract

n-Type semiconducting polymers with high thermoelectric performance remain challenging due to the scarcity of molecular design strategy, limiting their applications in organic thermoelectric (OTE) devices. Herein, we provide a new approach to enhance the OTE performance of n-doped polymers by introducing acceptor-acceptor (A-A) type backbone bearing branched ethylene glycol (EG) side chains. When doped with 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (N-DMBI), the A-A homopolymer PDTzTI-TEG exhibits n-type electrical conductivity (σ) up to 34 S cm⁻¹ and power factor value of 15.7 μW m⁻¹ K⁻². The OTE performance of PDTzTI-TEG is far greater than that of homopolymer PBTI-TEG (σ=0.27 S cm⁻¹), indicating that introducing electron-deficient thiazole units in the backbone further improves the n-doping efficiency. These results demonstrate that developing A-A type polymers with EG side chains is an effective strategy to enhance n-type OTE performance.

Three polymer analogues to polyaniline (PANI), PANI–carbazole (P1), PANI–phenoxazine (P2), and PANI–phenothiazine (P3) are designed with different energy levels to modify the interface between poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) and the MAPbI₃-based perovskite layer and improve the device performance. The order of contribution for the three effects of the polymer modification is work function adjustment > surface modification > perovskite growth control.

Abstract

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a popular hole transport material in perovskite solar cells (PSCs). However, the devices with PEDOT:PSS exhibit large open-circuit voltage (V _oc) loss and low efficiency, which is attributed to mismatched energy level alignment and the poor interface of PEDOT:PSS and perovskite. Here, three polymer analogues to polyaniline (PANI), PANI–carbazole (P1), PANI–phenoxazine (P2), and PANI–phenothiazine (P3) are designed with different energy levels to modify the interface between PEDOT:PSS and the perovskite layer and improve the device performance. The effects of the polymers on the device performance are demonstrated by evaluating the work function adjustment, perovskite growth control, and interface modification in MAPbI₃-based PSCs. Low bandgap Sn–Pb-based PSCs are also fabricated to confirm the effects of the polymers. Three effects are evaluated through the comparison study of PEDOT:PSS-based organic solar cells and MAPbI₃ PSCs based on the PEDOT:PSS modified by P1, P2, and P3. The order of contribution for the three effects is work function adjustment > surface modification > perovskite growth control. MAPbI₃ PSCs modified with P2 exhibit a high V _oc of 1.13 V and a high-power conversion efficiency of 21.06%. This work provides the fundamental understanding of the interface passivation effects for PEDOT:PSS-based optoelectronic devices.

Commercialization of all-perovskite tandem solar cells requires both, a thermally stable narrow-bandgap perovskite and a tunnel junction. Here all-FA Pb-Sn perovskite with superior intrinsic thermal stability and metal-oxide-based tunnel junction are deployed synchronously, which resulted in a power conversion efficiency of 26.3% and much improved thermal stability in all-perovskite tandem solar cells.

Abstract

Commercialization of all-perovskite tandem solar cells requires thermally stable narrow-bandgap (NBG) perovskites and tunnel junction. However, the high content of methylammonium (MA) and organic hole transport layer used in NBG perovskite subcell undermine the thermal stability of all-perovskite tandems. Here, thermally stable mixed lead-tin NBG perovskite solar cells (PSCs) are developed by using only formamidinium (FA) for the A-site cation. Solution-processed indium tin oxide nanocrystals (ITO NCs) are deployed further to replace the conventional organic charge transport layer. Meanwhile, the ITO NCs layer simultaneously functions as a recombination layer in the tunnel junction, which simplifies the architecture of all-perovskite tandem devices. The thermally stable all-FA Pb-Sn PSCs achieve a high power conversion efficiency (PCE) of 21.0%. With the thermally stable all-FA NBG perovskite and optimized tunnel junction, a stabilized PCE of 26.3% is further obtained in all-perovskite tandems. The unencapsulated tandem devices maintain >90% of their initial efficiencies after 212 h aging at 85 °C in the N₂ atmosphere. The strategies herein offer a crucial step toward efficient and thermally stable all-perovskite tandem solar cells.

Solar-to-thermal Cl⁻ doped poly(3,4-ethylenedioxythiophene) (Cl-PEDOT coating is successfully integrated onto various substrates conformally by oCVD technique. Cl-PEDOT coating prepared based on oxidative chemical vapor deposition has many advantages: universality, low-cost, stability, scalability, and high-efficiency. The Cl-PEDOT coated substrates are used for solar steam generation, indoor humidity/thermal management and solar-driven viscous crude-oil cleaning, all of which achieved satisfactory performance.

Abstract

Converting renewable solar energy into manageable thermal energy is significant for diverse applications. Nevertheless, integrating multifunctional solar-to-heat coating on various substrates and achieving large-scale manufacture remains a challenge. Herein, Cl⁻ doped poly(3,4-ethylenedioxythiophene) (Cl-PEDOT) coating on multiple substrates is successfully created using oxidative chemical vapor deposition (oCVD) without to be restricted to the changeable substrate surface chemistry (e.g., wettability), sizes as well as dimensions (2D–3D). Partial Cl⁻ doping and spontaneously formed microstructures can remarkably enhance near-infrared absorption and hydrophilicity of coating. The Cl-PEDOT coating manifests many advantages: universality, scalability, low-cost, high efficiency, and stability. When used for solar steam generation, all Cl-PEDOT coated substrates represent reinforced evaporation performance. The universality makes it possible to optimize the evaporator performance by structural design. Structural design as optimized energy flow enables the pyramid array wood-based evaporator to set an evaporation record (≈1.19 kg m⁻² h⁻¹, ≈91%) under the weak-light (0.5 sun). Moreover, a greenhouse and a crude-oil cleaner are designed to achieve eco-friendly, energy-saving solar-driven heating/dehumidification, and crude-oil recovery without additional energy input. This study reveals that well-designed oCVD is a simple and straightforward way to engineer lightweight and thermally insulating polymers into multifunctional solar-to-thermal composites toward diverse solar-driven applications.

Organic planar heterojunctions are fabricated by matching the thickness of a non-fullerene acceptor to its exciton diffusion length. Additional hole transfer mediated by the exciton diffusion generates a photocurrent over 10 mA cm⁻² in the planar heterojunction. Well-defined planar interfaces reduce the dark leakage current, resulting in 83 times higher photodetector detectivity than the corresponding bulk heterojunction device.

Abstract

While non-fullerene acceptors (NFAs) have recently been demonstrated to exhibit long-range exciton diffusion, most organic photovoltaic and photodetector studies still focus on blended polymer: NFA systems. Herein, a 40 nm exciton diffusion length for IT4F excitons is determined, and it is demonstrated that sharp interface, planar heterojunction (PHJ) IT4F/PM6 devices with the IT4F layer thickness matched to this diffusion length yield optimized photovoltaic and photodetector performance. The PHJ devices yield an enhanced device open-circuit voltage relative to bulk heterojunction (BHJ) devices, associated with suppressed bimolecular recombination losses. The PHJ architecture also results in a ≈100-fold increase in electroluminescence (EL) quantum efficiency relative to the BHJ device, correlated with a shift from charge transfer state EL for the BHJ to IT4F exciton dominated EL for the PHJ, attributed to significant hole injection from PM6 into IT4F. Of particular note, the PHJ architecture is shown to suppress dark leakage current, resulting in 83 times higher photodetector detectivity at −2 V bias than the equivalent BHJ device.

Medium bandgap isomeric small molecule acceptors m-DTC-Cl-1 and m-DTC-Cl-2 with different chlorine substitution positions is designed and synthesized. The devices based on m-DTC-Cl-2 show better charge dynamics and film morphology. The monolithic tandem organic solar cell based on PTO2:m-DTC-Cl-2 as the front cell demonstrates a high efficiency of 18.8%.

Abstract

Tandem organic solar cell (TOSC), composed of the front and rear cells with complementary absorption, is effective device structure for surpassing the Shockley–Queisser limit of single-junction organic solar cells (OSCs). However, most of the medium bandgap (≈1.6 eV) organic photovoltaic materials for front cells in the TOSCs show considerable voltage losses. In this work, two medium bandgap (1.63 eV) isomeric small molecule acceptors m-DTC-Cl-1 and m-DTC-Cl-2 are synthesized with different chlorine substitution positions in 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC). The different chlorine substituted positions in IC groups show significant influences on the physicochemical properties, charge dynamics, morphology, and photovoltaic performance of the acceptors. Consequently, the OSC with PTO2 as polymer donor and m-DTC-Cl-2 as acceptor delivers a champion power conversion efficiency (PCE) of 14.1% with a high open circuit voltage of 1.05 V and a low nonradiative energy loss of 0.25 eV, which indicates that the OSC is an ideal candidate for the application as front cell in the TOSCs. Then, a monolithic TOSC is fabricated with the OSC based on PTO2:m-DTC-Cl-2 as front cell and the OSC based on PTB7-Th:BTPV-4Cl as rear cell, which demonstrates a high PCE of 18.8%.

Two small-molecule donors, namely T4 and T6, with different substituents on their selenophene conjugated units are developed, of which T4 with alkyland T6 with trialkylsilyl. The all-small-molecule organic solar cell based on T6:N3 yields a power conversion efficiency (PCE) as high as 16.03%, significantly higher than that based on T4:N3 (PCE = 12.61%).

Abstract

Fibrous interpenetrating network structure morphology is extremely crucial for all-small-molecule organic solar cells (ASM-OSCs) in achieving high power conversion efficiency (PCE). Rational molecular design and suitable posttreatment to the film are feasible methods to accomplish this goal. Herein, two small molecule donors, namely T4 and T6, with different substituents on their selenophene conjugated units, alkyl for T4 while trialkylsilyl for T6, are developed. Both as cast devices obtain poor PCEs (≈4.5%) when blending these two donors with N3 due to the oversize phase separation. Satisfactorily, the PCEs are dramatically increased after CS₂ annealing, which mainly originates from the favorable reorganization of donor and acceptor in the active layer, ultimately improving the phase separation and vertical electronic properties. As a result, the device based on trialkylsilyl-substituted T6 acquires a remarkable PCE of 16.03%, much higher than that of the blends of alkyl-substituted T4 and N3 (12.61%). The enhanced PCE of the T6-based device is attributed to the deeper HOMO energy levels, more obvious fibrous interpenetrating networks, and stronger molecular interaction between T6 and N3, as compared with T4-based ones. This study indicates that precise molecular design and the proper posttreatment process can be a brilliant approach for realizing highly efficient ASM-OSCs.

The adsorption energy generated by the Coulomb interaction between 2D GeSe and acceptor molecules enables 2D GeSe as a nucleation center to promote the crystallization and molecular orientation of acceptor molecules, which increases the power conversion efficiency of organic solar cells with 2D GeSe as the third component.

Abstract

In organic solar cells (OSCs), the crystalline morphologies of the donor and acceptor at the microscale play an important role. 2D GeSe with periodic structure and high carrier mobility is an ideal additive material for active layer of OSCs that can effectively improve the crystallinity and molecular orientation of the acceptor molecule ITIC. Here, 2D GeSe is introduced into the active layer of OSCs to adjust the morphology of active layer for the first time, the results show that the incorporation of 2D GeSe induces the crystallization of acceptor molecule and facilitates the formation of efficient bicontinuous interpenetrating charge transport networks, and effectively reduces carrier recombination in OSCs. The power conversion efficiency and lifetime of OSCs are obviously enhanced. More importantly, the results of first-principles calculation reveal that the interaction between 2D GeSe and ITIC guides the ITIC molecules to form a continuous conductive network. This study provides a method for the morphology regulation of the donor and acceptor domains in bulk heterojunctions, provides an idea for researching the interaction between 2D materials and organic molecules, and also indicates that 2D GeSe has good application prospects in photovoltaic devices.

Flexible large-area organic solar modules are fabricated by switching the bottom silver nanowires (AgNWs) electrode and the top Ag film electrode to avoid the detrimental effect of high surface roughness of AgNWs electrodes. The AgNWs-polymer top transparent electrode is fabricated by water transfer printing with improved mechanical robustness by a crosslinked polymer. 21 cm² flexible modules containing 10 subcells XX fabricated with a power conversion efficiency of 12.3%.

Abstract

Upscaling of efficient flexible organic solar cells (OSCs) is still a challenging task, where flexible transparent electrode is a key limiting factor. Silver nanowires (AgNWs) are widely used as flexible transparent electrodes to fabricate efficient small-area flexible OSCs, but the high surface roughness of AgNWs electrodes causes large leakage current and performance deterioration in large-area OSCs. In this study, it is reported that a strategy of switching the bottom AgNWs electrode and the top Ag film electrode to avoid the detrimental effect of the high surface roughness of AgNWs electrodes. Mechanical robustness of the AgNWs has been enhanced by introducing a cross-linked poly(sodium 4-styrenesulfonate) layer. The AgNWs-polymer transparent film is fabricated by water transfer printing as the top electrode. 21 cm² flexible organic modules containing 10 sub-cells are fabricated and delivered power conversion efficiencies of 12.3% with the design of switched electrodes.

Interfacial buffer layers have a decisive impact on the performance and stability of organic solar cells. This review summarizes representative hole transporting materials, including organics, graphene-based molecules, and transition metal oxides, in an attempt to highlight the role of hole transport layers in regulating charge transport, tuning energy levels, reducing potential barriers, and reducing interfacial recombination losses.

Abstract

Recently, organic solar cells (OSCs) have received rapid boosts in the power conversion efficiency (PCE), due to progresses in materials and device engineering. Several groups have reported champion PCEs over 19% in single-junction, ternary, and tandem OSCs. In addition to the concentrated focus on the new design of OSC active materials, buffer layer materials, used for the interface layer providing the functionalities of interface charge transport and collection in OSCs, are of critical importance for the optimization of PCE. Compared with the electron transport layers (ETL), the hole transport layers (HTLs) have received less attention and are still dominated by the commercial material poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), which has limitations for the efficiency and OSC device stability enhancement. In this Review, the recent progress in HTL materials, including the modifications for PEDOT:PSS, alternative HTL materials based on polymers and inorganic oxide materials, etc, is summarized. This review also provides a summative prospect aiming to help scientists apprehend the current possibilities and challenges in this field.

The possible origin of packing-orientation formation in conjugated polymer films is unraveled. The solution-state supramolecular structure of conjugated polymers, with the observation of reversible dimensionality transition, is found to play predominant roles in the solid-state packing orientation of the polymer chains, where edge-on and face-on textures are generated from solutions with 1D and 2D structures, respectively.

Abstract

The solid-state molecular orientation of conjugated polymers is of vital importance for their charge transport properties, where the edge-on orientation with π-stacking direction parallel to the surface is generally preferable to achieving high-mobility planar field-effect transistors. However, so far, little is known about the origin of packing-orientation formation in thin films. Here, it is shown that the solution-state supramolecular structure of widely studied PffBT4T-based polymers can be reversibly tuned between 1D worm-like and 2D lamellar structures for the same polymer/solvent system through solution temperature. Such dimensionality in solution determines the solid-state packing orientation of the polymer chains, where edge-on and face-on textures are generated from solutions with 1D and 2D structures, respectively. More importantly, the transition temperature of solution-state supramolecular dimensionality is in excellent agreement with that of solid-state packing orientation. These experimental observations unambiguously demonstrate the predominant roles of solution-state supramolecular assembly in solid-state molecular orientation, which is further verified using different molecular weight batches and other two representative polymers. The findings provide new insights into the growth mechanism of polymer semiconductors during transistor fabrication, and open prospective pathways for boosting device performance of solution-processable plastic electronics.

Organic Solar Cells

In article number 2200617, Tao Yang, Teng Zhang, Bingsuo Zou, Tao Liu, and co-workers applied a two-step annealing method in which solvent vapor annealing and thermal annealing are included, and successfully achieved 15% efficiency for block copolymer-based or single-component organic solar cells. This two-step annealing also pushes the non-halogenated solvent dissolved binary all-polymer solar cells towards > 17% efficiency.

All-polymer solar cells (PSCs) based on a new polymer acceptor PYSe-2FT exhibit highly efficient and mechanically robust properties with simple device technology of free treatment. Power conversion efficiencies of 13.56% also are the best values reported in flexible all-PSCs so far. Good flexibility, favorable universality, and stability hold great potential for future applications where high performances and mechanical stability are anticipated.

The many merits of organic solar cells such as light weight, flexibility, and printability rely heavily on flexible devices. In this regard, all-polymer solar cells (PSCs) are the primary choices due to the superior flexibility and mechanical properties of polymers over small molecule and fullerene materials. However, the polymer batch discrepancy and the multifarious post-treatment steps are serious obstacles to practical applications. Herein, highly efficient and mechanically robust all-PSCs based on a new polymer acceptor PYSe-2FT and polymer donor D18 are developed. Without any post-treatment, the flexible all-PSC exhibits high power conversion efficiency (PCE) of 13.56%, which stands among the best values in flexible all-PSCs so far. Bending tests reveal that the flexible device maintains 86% efficiency of the original PCE after 1000 bending cycles with a narrow curvature radius of 3 mm. More importantly, the all-PSC efficiencies are insensitive to the molecular weight of the newly developed acceptor polymer, which possesses favorable universality and stability when working together with various donors. The superior mechanical properties and the ease of process make this all-PSC a promising candidate for applications in flexible and portable devices.

A PEDOT:PSS-free structure from self-organized interlayer for pseudoplanar heterojunction organic solar cells is fabricated with excellent thickness-insensitivity feature. When active layer thickness increases from 100 to 300 nm, the PEDOT:PSS-free device delivers a decent degradation of fill factor from 78.4% to 72.9%, yielding an excellent power conversion efficiency (PCE) of 16.4%.

Thickness-insensitivity of organic solar cells (OSCs) is a crucial issue for transformation from the laboratory-scale devices to large-area solar panels. Generally, the low carrier mobility of organic semiconductors hindering charge transport process leads to severe recombination losses and further poisons the fill factor (FF) in thick-film OSCs. Herein, a PEDOT:PSS-free pseudoplanar heterojunction OSC from sequential deposition method with self-organized [2-(9H-carbazol-9-yl)ethyl]phosphonic acid interlayer is fabricated. The notable power conversion efficiency (PCE) enhancement from PEDOT:PSS-based device of 17.0% to PEDOT:PSS-free device of 17.8% is obtained in thin-film devices (≈100 nm), which is correlated to the improved incident photons absorption by the absence of PEDOT:PSS. Besides, the PEDOT:PSS-free device exhibits excellent thickness tolerance, with FF only degrades from 78.4% to 72.9% when the active layer thickness increases from ≈100 to ≈300 nm. The insights of remained FF are further traced to notably mitigated nongeminate recombination losses of PEDOT:PSS-free structure. The strengthened charge extraction is also verified by reinforced built-in potential and desirable and balanced mobilities. Consequently, the PEDOT:PSS-free device with ≈300 nm active layer yields an inspiring PCE of 16.4%, much higher than that of PEDOT:PSS-based device of 14.5%.

MPhS-C2 with shortened terminal alkyl chain, features thermal annealing (TA)-insensitive aggregation and condense packing, leading to suppressed upshifts of highest occupied molecular orbital energy level during TA, and efficient charge transport at small phase separation in BTP-eC9 blended devices, obtaining the highest PCE of 17.11% with ΔV _nr of 0.192 V in ASM-OSCs.

Abstract

A critical bottleneck for further efficiency breakthroughs in organic solar cells (OSCs) is to minimize the non-radiative energy loss (eΔV _nr) while maximizing the charge generation. With the development of highly emissive low-bandgap non-fullerene acceptors, the design of high-performance donors becomes critical to enable the blend with the electroluminescence quantum efficiency to approach or surpass the pristine acceptor. Herein, by shortening the end-capped alkyl chains of the small-molecular donors from hexyl (MPhS-C6) to ethyl (MPhS-C2), the material obtained aggregation that was insensitive to thermal annealing (TA) along with condensed packing simultaneously. The former leads to small phase separation and suppressed upshifts of the highest occupied molecular orbital energy level during TA, and the latter facilitates its efficient charge-transport at aggregation-less packing. Hence, the ΔV _nr decreases from 0.242 to 0.182 V, from MPhS-C6 to MPhS-C2 based OSCs. An excellent PCE of 17.11% is obtained by 1,8-diiodoctane addition due to almost unchanged high J _sc (26.6 mA cm⁻²) and V _oc (0.888 V) with improved fill factor, which is the record efficiency with the smallest energy loss (0.497 eV) and ΔV _nr (0.192 V) in all-small-molecule OSCs. These results emphasize the potential material design direction of obtaining concurrent TA-insensitive aggregation and condensed packing to maximize the device performances with a super low ΔV _nr.

Regulation of the configurations of the non-conjugated polymer acceptors enables green solvent-processed large-area binary all-polymer solar cells to achieve record efficiency and robustness. This study not only provides a series of reliable novel conductive materials with excellent performance for flexible wearable solar cells but also elucidates a concept to evaluate the comprehensive performance of organic solar cells.

Abstract

With the great potential of the all-polymer solar cells for large-area wearable devices, both large-area device efficiency and mechanical flexibility are very critical but attract limited attention. In this work, from the perspective of the polymer configurations, two types of terpolymer acceptors PYTX-A and PYTX-B (X = Cl or H) are developed. The configuration difference caused by the replacement of non-conjugated units results in distinct photovoltaic performance and mechanical flexibility. Benefiting from a good match between the intrinsically slow film-forming of the active materials and the technically slow film-forming of the blade-coating process, the toluene-processed large-area (1.21 cm²) binary device achieves a record efficiency of 14.70%. More importantly, a new parameter of efficiency stretchability factor (ESF) is proposed for the first time to comprehensively evaluate the overall device performance. PM6:PYTCl-A and PM6:PYTCl-B yield significantly higher ESF than PM6:PY-IT. Further blending with non-conjugated polymer donor PM6-A, the best ESF of 3.12% is achieved for PM6-A:PYTCl-A, which is among the highest comprehensive performances.

A novel but efficient terpolymer strategy by introducing highly electron deficient pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione block with high molecular dipole resolves the tradeoff between intermolecular interaction and backbone disorder well, facilitating the optimization of blend morphology and elevating the fill factor and power conversion efficiency to a high level.

Abstract

Constructing terpolymer has attracted increasing attention as a strategy to improve the performance of polymer solar cell. Terpolymer usually offers an opportunity to lower the frontier molecular orbital energy level, introduces additional absorption band and sometimes optimizes the morphology of the active blend. Generally, the additional segment in terpolymer backbone inevitably introduces backbone disorder, which causes entropy rises. However, selecting a suitable dipole unit introduces extra driving forces for crystallization by enhancing intermolecular interactions. This provides a handy knob for tradeoff between intermolecular interaction and backbone disorder, thus regulating the blend morphology. Herein, a high dipole and electron-deficient group of pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione (TzBI) is incorporated into the high-performance donor polymer and a series of terpolymers with different content of TzBI are designed. As expected, the morphology is optimized gradually for improving charge generation and charge transport, also suppressing charge recombination. The champion device with 10% TzBI exhibited a power conversion efficiency (PCE) of 18.36%, which is 5% increase compared to the controlled device. This study presents a charming terpolymer strategy by highly electron-deficient and high dipole segment to realize a tradeoff between intermolecular interaction and backbone disorder, facilitating the optimization of morphology and elevation of fill factor and device efficiency.

Organic Photovoltaics

In article number 2203487, Chieh-Ting Lin, Chu-Chen Chueh, and co-workers systematically investigate the water-immersion stability among a series of organic donors/acceptors and electron transporting layers. This work presents a strategy to develop water-insensitive organic photovoltaics by combining the use of a nanoparticle titanium dioxide electron transporting layer and all-polymer bulk heterojunction blends, which shows stable morphology and charge transfer kinetics after water immersion.

The effects of sulphur atoms positions of dithienothiophene on electronic property of hole-transport materials and performances of perovskite solar cells are systematically investigated. The positional variation of sulphur atoms in dithienothiophene not only gradually improves electron delocalization and enhances hole mobility but also effectively suppresses nonradiative recombination of perovskite solar cells.

Abstract

Hole transport materials (HTMs) are of great significance to improve the efficiency and long-term stability of perovskite solar cells (PVSCs). Herein, a series of new HTMs based on isomeric dithienothiophene (DTT) are designed and synthesized. Effects of sulphur (S) atoms positions on defect passivation and performance of PVSCs are systematically investigated through theoretical computation, X-ray diffraction, X-ray photoelectron spectroscopy, etc. The three molecules display noticeable isomeric effect in energy level, light absorption, and hole mobility. With S atoms varied from bottom-bottom-bottom in 3T-1 to bottom-bottom-top in 3T-2, then to bottom-top-bottom in 3T-3, the grown perovskite crystallite on the corresponding HTMs shows more homeogenous film morphology and less pinhole traps. Meanwhile, nonradiative recombination losses can be suppressed and hole extraction efficiency at HTM/perovskite surface can be improved from 3T-1 to 3T-3. As a result, the remarkable improvement of short-circuit current density nd open-circuit voltage in inverted perovskite solar cells can be realized with increasing the sulphur atoms contribution to the molecular conjugation. More importantly, 3T-3-based dopant-free HTM achieves a top power conversion efficiency of 19.23% in PVSCs with good device stability under green solvent processing. These results demonstrate the role of S atoms positions in HTMs on photovoltaic performance of PVSCs and the potential of DTT in developing eco-friendly HTMs toward efficient PVSCs.