Blade-coated organic solar cells from non-halogenated solvent offer 17%efficiency

Organic solar cell(OSC)has attracted great interests due to its potential applications[1-9].To date,18%power conversion efficiency(PCE)has been achieved in single-junction OSC[10−13],indicating the feasibility of commercialization.This photovoltaic technology currently faces the performance gap between laboratory cells and large-area modules.

苯基取代苯并二噻吩二酮构建新型聚合物及其光伏性能研究

随着材料和器件的不断发展,有机光伏(OPV)的器件效率不断提升,但制备仍存在较多额外加工工艺,不利于其大规模生产.如何合理调控活性层材料的溶解性、结晶性和两相形貌来简化器件制备工艺,实现高性能的as-cast器件将十分具有科学意义.本工作通过设计合成苯基取代的苯并二噻吩二酮单元(二维BDD)作为共聚单元,制备了三种新型聚合物材料.当二维BDD单元摩尔分数为10%时, FBDT-m10能实现良好的聚集性能和加工性能,与Y6-BO共混制备的as-cast器件就可以得到良好的活性层形貌,最终实现了71.14%的填充因子及16.06%的器件效率.

Replacing alkyl side chain of non-fullerene acceptor with siloxane-terminated side chain enables lower surface energy towards optimizing bulk-heterojunction morphology and high photovoltaic performance

Towards a good control of the morphology of bulk-heterojunction(BHJ)active layers for polymer solar cells(PSCs),selecting an appropriate side chain for a polymer donor and a nonfullerene acceptor(NFA)is very crucial.In this work,two novel NFAs i-IE-4F and i-IESi-4 F comprising alkyl and siloxane-terminated side chains on the central indacenodithiophene(IDT)core,respectively,were synthesized.Attaching the siloxane-terminated side chain to i-IESi-4 F affords surface energy(γ)of33.32 mN/m,much lower than that of 39.83 mN/m for i-IE-4F,supplying a big chance to tune miscibility with a polymer donor.Two fluorobenzotriazole-based polymer donors J52 and PBZ-2Si bearing alkyl and siloxane-terminated side chains,respectively,showγvalues of 36.08 and 33.10 mN/m,respectively.The estimated Flory-Huggins interaction parameters(χD,A)indicate that the i-IESi-4 F is more miscible than i-IE-4F in pairing with J52 or PBZ-2Si.The resulting i-IESi-4 F-based blend film exhibits low film roughness and accompanies obviously improved BHJ uniformity.In PSCs,the J52:i-IESi-4F and PBZ-2Si:i-IESi-4 F active layers display power conversion efficiencies(PCEs)of 12.67%and 14.54%,respectively,all remarkably higher than PCEs≤7.34%of the i-IE-4F-based active layers.Interestingly,the PBZ-2Si:i-IESi-4 F active layer,a donor:acceptor blend system comprising siloxane-terminated side chains(DSi:ASimatching)with the highest BHJ miscibility due to the combinatory effect of the side chains,shows the highest efficiency,as supported by efficient exciton dissociation,the lowest bimolecular recombination,and the optimal charge transport.Our results demonstrate that attaching siloxane-terminated side chains to NFAs,as a side chain engineering,has big potential in lowering their surface energy towards fine control of BHJ morphology and leading to a better donor:acceptor blend system.

Low band-gap benzodithiophene-thienothiophenecopolymers: the effect of dual two-dimensional substitutions on optoelectronic properties

Two new conjugated copolymers,PBDT-T6-TTF and PBDT-T12-TTF,were derived from a novel 4-fluorobenzoyl thienothiophene(TTF).In addition,two types of benzodithiophene(BDT)units with 2,3-dihexylthienyl(T6)and 2,3-didodecylthienyl(T12)substituents,respectively,were successfully synthesized.The effect of the dual two-dimensional(2D)substitutions of the building blocks upon the optoelectronic properties of the polymers was investigated.Generally,the two polymers exhibited good solubility and broad absorption,showing similar optical band gaps of^1.53 e V.However,PBDT-T6-TTF with its shorter alkyl chain length possessed a larger extinction coefficient in thin solid film.The highest occupied molecular orbital(HOMO)level of PBDT-T6-TTF was located at–5.38 e V while that of PBDT-T12-TTF was at–5.51 e V.In space charge-limitedcurrent(SCLC)measurement,PBDT-T6-TTF and PBDT-T12-TTF displayed respective hole mobilities of 3.0×10–4 and1.6×10–5 cm2 V1 s1.In polymer solar cells,PBDT-T6-TTF and PBDT-T12-TTF showed respective power conversion efficiencies(PCEs)of 2.86%and 1.67%.When 1,8-diiodooctane(DIO)was used as the solvent additive,the PCE of PBDT-T6-TTF was remarkably elevated to 4.85%,but the use of DIO for the PBDT-T12-TTF-blend film resulted in a lower PCE of 0.91%.Atomic force microscopy(AFM)indicated that the superior efficiency of PBDT-T6-TTF with 3%DIO(v/v)should be related to the better continuous phase separation of the blend film.Nevertheless,the morphology of the PBDT-T12-TTF deteriorated when the 3%DIO(v/v)was added.Our results suggest that the alkyl-chain length on the 2D BDT units play an important role in determining the optoelectronic properties of dual 2D BDT-TT-based polymers.

Silaindacenodithiophene-Based Fused-Ring Non-Fullerene Electron Acceptor for Efficient Polymer Solar Cells

In this work, a new A-D-A type nonfuUerene small molecular acceptor SilDT-IC, with a fused-ring silaindacenodithiophene （SilDT） as D unit and 2-（3-oxo-2,3-dihydroinden-l-ylidene）malononitrile （INCN） as the end A unit, was design and synthesized. The SilDT-IC film shows absorption peak and edge at 695 and 733 nm, respectively. The HOMO and LUMO of SilDT-IC are of -5.47 and -3.78 eV, respectively. Compared with carbon-bridging, the Si-bridging can result in an upper-lying LUMO level of an acceptor, which is benefit to achieve a higher open-circuit voltage in polymer solar cells （PSCs）. Complementary absorption and suitable energy level alignment between SilDT-IC and wide bandgap polymer donor PBDB-T were found. For the PBDB-T：SilDT-IC based inverted PSCs, a D/A ratio of 1 ： 1 was optimal to achieve a power conversion efficiency （PCE） of 7.27%. With thermal annealing （TA） of the blend film, a higher PCE of 8.16% could be realized due to increasing of both short-circuit current density and fill factor. After the TA treatment, hole and electron mobilities were elevated to 3.42 × 10-4 and 1.02 × 10-4 cm2·V-1.s-1, respectively. The results suggest that the SilDT, a Si-bridged fused ring, is a valuable D unit to construct efficient nonfullerene acceptors for PSCs.