Simultaneous Optimization of Efficiency,Stretchability,and Stability in All-Polymer Solar Cells via Aggregation Control

With the emergence of Y-series small molecule acceptors,polymerizing the small molecule acceptors with aromatic linker units has attracted significant research attention,which has greatly advanced the photovoltaic performance of all-polymer solar cells.Despite the rapid increase in efficiency,the unique characteristics(e.g.,mechanical stretchability and flexibility)of all-polymer systems were still not thoroughly explored.In this work,we demonstrate an effective approach to simultaneously improve device performance,stability,and mechanical robustness of all-polymer solar cells by properly suppressing the aggregation and crystallization behaviors of polymerized Y-series acceptors.Strikingly,when introducing 50 wt%PYF-IT(a fluorinated version of PY-IT)into the well-known PM6:PY-IT system,the all-polymer devices delivered an impressive photovoltaic efficiency of 16.6%,significantly higher than that of the control binary cell(15.0%).Compared with the two binary systems,the optimal ternary blend exhibits more efficient charge separation and balanced charge transport accompanying with less recombination.Moreover,a high-performance 1.0 cm^(2)large-area device of 15%efficiency was demonstrated for the optimized ternary all-polymer blend,which offered a desirable PCE of 14.5%on flexible substrates and improved mechanical flexibility after bending 1000 cycles.Notably,these are among the best results for 1.0 cm^(2)all-polymer OPVs thus far.This work also heralds a bright future of all-polymer systems for flexible wearable energy-harvesting applications.

Refining acceptor aggregation in nonfullerene organic solar cells to achieve high efficiency and superior thermal stability

With the rapid increase in photoelectric conversion efficiency of organic photovoltaics(OPVs),prolonging the operational lifetime of devices becomes one of the critical prerequisites for commercial applications.Guided by the theoretical calculations of molecular stacking and miscibility,we proposed an effective approach to simultaneously improve device performance and thermal stability of high-efficiency OPVs by refining the aggregation of Y-series acceptors.The key to this approach is deliberately designing an asymmetric Y-series acceptor,named Y6-CNO,which acts as a third component regulator to finely tune the degree of acceptor aggregation and crystallization in the benchmark PM6:Y6-BO system.Strikingly,a champion photovoltaic efficiency of 18.0%was achieved by introducing 15 wt%Y6-CNO into the PM6:Y6-BO system,significantly higher than the control binary cell(16.7%).Moreover,annealing at 100°C for over 1,200 h does not markedly affect the photovoltaic performance of the optimal ternary devices,maintaining above 95%of the initial performance and exhibiting an exceptionally high T_(80)lifetime of 9,000 h under continuous thermal annealing.By contrast,binary devices suffer from excessive crystallization of acceptors with long-term annealing.Additionally,mixing thermodynamics combined with morphological characterizations were employed to elucidate the microstructure-thermal stability relationships.The ternary OPVs consisting of symmetric and asymmetric homologous acceptors form better charge transport channels and can effectively suppress excessive aggregation of acceptors under long-term annealing.This work demonstrates the effectiveness of refining acceptor aggregation via molecular design for highly efficient and stable nonfullerene-based OPVs.

Multifunctional all-polymer photovoltaic blend with simultaneously improved efficiency(18.04%),stability and mechanical durability

One of the most appealing material systems for solar energy conversion is allpolymer blend.Presently,the three key merits(power conversion efficiency,operation stability and mechanical robustness)exhibited a trade-off in a particular all-polymer blend system,which greatly limit its commercial application.Diverting the classic ternary tactic of organic solar cells based on polymer,nonfullerene small molecule and fullerene,herein we demonstrate that the three merits of a benchmark all-polymer blend PM6:PY-IT can be simultaneously maximized via the introduction of a polymerized fullerene derivative PPCBMB.Importantly,the addition of the guest component promoted the power conversion efficiency of PM6:PY-IT blend from 16.59%to 18.04%.Meanwhile,the device stability and film ductility are also improved due to the addition of this polymerized fullerene material.Morphology and device physics analyses reveal that optimal ternary system contains well-maintained molecular packing and crystallinity,being beneficial to keeping favorable charge transport and the reduced domain size contributed to charge generation and ductility improvement.Furthermore,the ternary photovoltaic blend was successfully used as photocatalysts,and an excellent heavy metal removal from water was demonstrated.This study showcases the multi-functions of all-polymer blends via the use of polymerized fullerenes.

A generic approach yields organic solar cells with enhanced efficiency and thermal stability

The use of deuterium are critical for promoting the fundamental understanding of aggregate materials and their new functions.Particularly,the solution structure of conjugated polymers can be hardly resolved without deuteration.However,studies about the isotopic effects of casting solvents on the aggregated structures of photovoltaic polymers and their bulk-heterojunction blends are deficient.Here,the impact of deuterated solvents on the thermal behavior,aggregated structures,and device performance of photovoltaic polymers is clearly delineated for the first time by multiple techniques.The enhanced π-π stacking order of photovoltaic polymers is highly relevant to their relatively poor miscibility with deuterated solvents.Benefiting from higher crystallinity and optimized morphology of deuterated solvents processed films,the devices are able to achieve better efficiency and notable improvement in thermal stability.Our results highlight the isotopic effects of solvents on the aggregated structure of conjugated polymer systems and reveal the potential of innovative approaches to fabricate thermally stable high-efficiency solar cells.

Printable and stable all-polymer solar cells based on non-conjugated polymer acceptors with excellent mechanical robustness

All-polymer solar cells(all-PSCs)trigger enormous commercial applications,and great progress has been made in recent years.However,from small-area devices to large-area modules,the poor adaption of the materials for printing methods and the large efficiency loss are still great challenges.Herein,three novel non-conjugated polymer acceptors(PTH-Y,PTClm-Yand PTClo-Y)are developed for all-PSCs.It can be found that non-conjugated polymer acceptors can effectively minimize the technique and efficiency gaps between small-area spin-coating and large-area blade-printing method,which can facilitate the preparation of large-area flexible device.By directly inheriting the spin-coating condition,the blade-coating processed device based on PTCloY achieves an impressive power conversion efficiency(PCE)of 12.42%,comparable to the spin-coating processed one(12.74%).Such a non-conjugated polymer system also can well tolerate large-scale preparation and flexible substrate.Notable PCE of 11.94%for large-area rigid device and 11.56%for large-area flexible device are obtained,which is the highest value for large-area flexible all-PSCs fabricated by blade-coating.In addition,the non-conjugated PTClo-Y-based devices show excellent thermal stability and mechanical robustness.These results demonstrate that the non-conjugated polymer acceptors are potential candidates for the fabrication of highly-efficient,large-area and robust flexible all-PSCs by printing methods.

Morphology control in high-efficiency all-polymer solar cells

All-polymer solar cells(All-PSCs)have attracted tremendous research interest in the recent decade due to the great potentials in stretchable electronic applications in terms of long-term stability and mechanical stretchability.Driven by the molecular design of novel polymer acceptors and morphology optimization,the power conversion efficiency(PCE)of All-PSCs has developed rapidly and now exceeded 17%.This review outlines the promising strategies for high-performance All-PSCs from the aspect of morphology control with the motivation to rationally guide the optimization.In this review,we briefly discuss the thermodynamic mixing principles of all-polymer blends and the effects of the molecular structure of conjugated polymers on thin-film morphology in All-PSCs.The crucial role of molecular miscibility in influencing morphological features and performance metrics was highlighted.We also expound on the effective methods of controlling film morphology through properly tuning the aggregation behavior of polymers.In particular,insightful studies on the commonly used naphthalene diimide-based acceptor polymers and the newly emerging polymerized nonfullerene small molecule acceptors(ITIC-series,Y6-series,etc)are discussed in detail.Finally,we present an outlook on the major challenges and the new opportunities of All-PSCs for efficiency breakthroughs targeting 20%.

Flexible conductive polymer composites for smart wearable strain sensors

Wearable strain sensors based on flexible conductive polymer composites(FCPCs)have attracted great attention due to their applications in the fields of human–machine interaction,disease diagnostics,human motion detection,and soft robotic skin.In recent decades,FCPC‐based strain sensors with high stretchability and sensitivity,short response time,and excellent stability have been developed,which are expected to be more versatile and intelligent.Smart strain sensors are required to provide wearable comfort,such as breathability,selfcooling ability,and so forth.To adapt to the harsh environment,wearable strain sensors should also be highly adaptive to protect the skin and the sensor itself.In addition,portable power supply system,multisite sensing capability,and multifunctionality are crucial for the next generation of FCPC‐based strain sensor.

Thermally stable poly(3-hexylthiophene):Nonfullerene solar cells with efficiency breaking 10%

Solar cells featuring polythiophenes as donors are one of the optoelectronic devices that hold notable promises for commercial application,profiting from the lowest synthetic complexity and excellent scalability.However,the complex phase behaviors of polythiophenes and their blends put constraints on modulating electrical performance and thus realizing stable performance under thermal stress.In this contribution,we present a multi-technique approach that combines calorimetry,scattering,spectroscopy,and microscopy to thoroughly probe the thermodynamic mixing,thermal properties of materials,the evolution of nanoscale domain structure,and device performance of poly(3-hexylthiophene)(P3HT)with a range of nonfullerene acceptors(NFAs)such as ITIC,IDTBR,and ZY-4Cl.Accordingly,two blending guidelines are established for matching these popular NFAs with P3HT to enable highly efficient and thermally stable cells.First,blend systems with weak vitrification and hypo-miscibility are excellent candidates for efficient solar cells.Furthermore,high thermal stability can be achieved by selecting NFAs with diffusion-limited crystallization.The P3HT:ZY-4Cl blend was found to endow the best performance of over 10%efficiency and an exceptionally high T_(80) lifetime of>6000 h under continuous thermal annealing,which are among the highest values for P3HT-based solar cells.This realization of high thermal stability and efficiency demonstrates the remarkable potentials of simple polythiophene:nonfullerene pairs in electronic applications.