Shorter alkyl chain in thieno[3,4-c]pyrrole-4,6-dione(TPD)-based large bandgap polymer donors – Yield efficient non-fullerene polymer solar cells

Typically,conjugated polymers are composed of conjugated backbones and alkyl side chains.In this contribution,a cost-effective strategy of tailoring the length of alkyl side chain is utilized to design highperforming thieno[3,4-c]pyrrole-4,6-dione(TPD)-based large bandgap polymer donors PBDT-BiTPD(Cχ)(χ=48,52,56),in which x represents the alkyl side chain length in term of the total carbon number.A combination of light absorption,device,and morphology examinations make clear that the shorter alkyl side chains yield(i) higher crystallinity and more predominant face-on crystallite orientation in their neat and BHJ blend films,(ii) higher charge mobilities(6.7×10^(-4) cm~2 V^(-1) s^(-1) for C48 vs.3.2×10^(-4) cm~2 V^(-1) s^(-1) for C56),and negligible charge recombination,consequently,(iii) significantly improved fill-factor(FF) and short current(J_(SC)),while almost the same open circuit voltage(V_(OC)) of ca.0.82 V in their corresponding BHJ devices.In parallel,as alkyl side chain lengths decrease from C56 to C48,power conversion efficiencies(PCEs) increased from 7.8% for C56 to 11.1% for C52,and further to14.1% for C48 in their BHJ solar cells made with a narrow bandgap non-fullerene acceptor Y6.This systematic study declares that shortening the side chain,if providing appropriate solubility in device solution processing solvents,is of essential significance for developing high-performing polymer donors and further improving device photovoltaic performance.

Altering alkyl-chains branching positions for boosting the performance of small-molecule acceptors for highly efficient nonfullerene organic solar cells

The emergence of the latest generation of small-molecule acceptor(SMA)materials,with Y6 as a typical example,accounts for the surge in device performance for organic solar cells(OSCs).This study proposes two new acceptors named Y6-C2 and Y6-C3,from judicious alteration of alkyl-chains branching positions away from the Y6 backbone.Compared to the Y6,the Y6-C2 exhibits similar optical and electrochemical properties,but better molecular packing and enhanced crystallinity.In contrast,the Y6-C3 shows a significant blue-shift absorption in the solid state relative to the Y6 and Y6-C2.The as-cast PM6:Y6-C2-based OSC yields a higher power conversion efficiency(PCE)of 15.89%than those based on the Y6(15.24%)and Y6-C3(13.76%),representing the highest known value for as-cast nonfullerene OSCs.Prominently,the Y6-C2 displays a good compatibility with the PC71BM.Therefore,a ternary OSC device based on PM6:Y6-C2:PC71BM(1.0:1.0:0.2)was produced,and it exhibits an outstanding PCE of 17.06%and an impressive fill factor(FF)of 0.772.Our results improve understanding of the structureproperty relationship for state-of-the-art SMAs and demonstrate that modulating the structure of SMAs via fine-tuning of alkylchains branching positions is an effective method to enhance their performance.

界面优化实现寿命超过20年的有机太阳电池

近年来,由于新型非富勒烯受体材料的快速发展,诸多中国科学家在有机太阳电池(OPV)的能量转换效率(PCE)上取得了重大突破.为了实现OPV的产业化,目前亟待解决的难题在于提升OPV的使用寿命,并降低大面积模组器件的效率滚降.本文提出了一种简易而有效的阴极界面修饰方法,成功实现了非富勒烯有机太阳电池超过20年的使用寿命.文章采用自组装小分子C60-SAM对氧化锌阴极界面进行修饰,不仅可以调控氧化锌和活性层之间的表面能匹配及其分子间相互作用来得到形貌更稳定的器件,同时还能通过钝化氧化锌表面缺陷以提升电池器件的电荷抽取效率.在此基础上,作者基于PTB7-Th:IEICO-4F制备得到PCE=10%,持续光照下寿命长达34000 h的OPV器件.根据中国平均每年1500 kWh/m2太阳辐射量推算,该OPV器件的使用寿命可超过20年.这将为OPV技术实现商业化带来极强曙光.

High-performance all-polymer solar cells with only 0.47 eV energy loss

The field of all-polymer solar cells(all-PSCs)has experienced rapid development during the past few years,mainly driven by the development of efficient polymer acceptors.However,the power conversion efficiencies(PCEs)of the all-PSCs are still limited by insufficient light absorption of the donor/acceptor blend and large energy loss in devices.We herein designed a polymer acceptor PYT1 constructed n-type molecular acceptor Y5-C20 as the key building block and blended it with a polymer donor PM6 to obtain an all-polymer photoactive layer.The optimized PM6:PYT1 all-PSCs achieved a record higher PCE of 13.43%with a very low energy loss of 0.47 eV and a photoresponse of up to 900 nm compared with the Y5-C20 based device with a best PCE of 9.42%.Furthermore,the PCEs of the PM6:PYT1 all-PSCs are relatively insensitive to the 1-chloronaphthalene(CN)additive contents and active layer thickness.Our results also highlight the effect of CN additive on PM6:PYT1 morphology,i.e.,charge generation,and transport find an optimized balance,and radiative and non-radiative loss is simultaneously reduced in the blend.This work promotes the development of high-performance polymer acceptors and heralds a brighter future of all-PSCs for commercial applications.

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.

Fundamental understanding of high-capacity lithium-excess cathodes with disordered rock salt structure

As a new class of lithium rich cathodes,disordered rock-salt cathodes have been of primary interest,because of their ability to deliver a promisingly high capacity up to 300 mAh/g.Nevertheless,some fundamental issues are yet to be fully understood and a comprehensive mastering of their solid-state chemistry,kinetics and thermal stability is required.Here,we select a high capacity cation-disordered positive electrode-Li_(1.2)Ni_(0.4)Nb_(0.4)O_(2)as a model compound to study intrinsic reaction mechanism,including charge compensation mechanism,kinetics,thermal stability,and structural evolution.By combining soft and hard X-ray absorption spectroscopy(XAS),X-ray photoelectron spectroscopy(XPS)with operando and exsitu differential scanning calorimetry(DSC),galvanostatic intermittent titration technique(GITT),cyclic voltammetry(CV),and X-ray diffraction(XRD),we present holistic information on disordered rock-salt cathode.This work provides beneficial insights into designing and tailoring new positive electrodes with disordered rock-salt structure.