Two benzo[1,2-b:4,5-b￠]dithiophene(BDT)-based small molecule(SM) donor materials with identical conjugated backbones but different substitution groups, named as DRTB-O and DRTB-T, were well explored to demonstrate the influence of the replacement of alkoxy with alkylthienyl on their photovoltaic properties in fullerene-based and fullerene-free organic solar cells(OSCs). The study shows that the two SM donors possess similar absorption spectra and energy levels but different crystalline structures in solid films. The carrier transport property and phase separation morphologies of the blend films have also been fully investigated.By employing PC71 BM as the acceptor, the power conversion efficiency(PCE) of DRTB-O:PC71BM and DRTB-T:PC71BM based devices were 4.91% and 7.08%, respectively. However, by blending with IDIC, the two SM donors exhibited distinctly different photovoltaic properties in fullerene-free OSCs, and the PCE of DRTB-O:IDIC and DRTB-T:IDIC based devices were 0.15% and9.06%, respectively. These results indicate that the replacement of alkoxyl with alkylthienyl in designing SM donor materials plays an important role in the application of fullerene-free OSCs.
A new benzodithiophene （BDT）-alt-fluorobenzotriazole （FBTA） D-A copolymer J40 was designed and synthesized by introducing 2-octyldodecyloxy side chains on its BDT units, for expanding the family of the BDT- alt-FBTA-based copolymers and investigating the side chain effect on the photovoltaic performance of the polymer in non-fullerene polymer solar cells （PSCs）. J40 exhibits complementary absorption spectra and matched electronic energy levels with the n-type organic semiconductor （n-OS） （3,9-bis（2-methylene-（3-（1,1-dicyanomethylene）-indanone））-5,5,11,11-tetrakis（4-hexylphenyl）-dithieno[2,3-d：2＇,3＇-d＇]-s- indaceno[1,2-b：5,6-b＇]dithiophene） （ITIC） acceptor, and was used as polymer donor in the non-fullerene PSCs with ITIC as acceptor. The power conversion efficiency （PCE） of the PSCs based on J40：ITIC （1：1, w/w） with thermal annealing at 120 ~C for l0 min reached 6.48% with a higher open-circuit voltage （Voc） of 0.89 V. The high Voc of the PSCs is benefitted from the lower-lying highest occupied molecular orbital （HOMO） energy level of J40. Although the photovoltaic performance of the polymer J40 with alkoxy side chain is lower than that of J60 and J61 with alkylthio-thienyl conjugated side chains, the PCE of 6.48% for the J40-based device is still a relatively higher photovoltaic efficiency in the non-fullerene PSCs reported so far. The results indicate that the family of the BDT-alt-FBTA-based D-A copolymers are high performance polymer donor materials for non-fullerene PSCs and the side chain engineering plays an important role in the design of high performance polymer donors in the non-fullerene PSCs.
Haijun BinLian ZhongZhi-Guo ZhangLiang GaoYankang YangLingwei XueJing ZhangZhanjun ZhangYongfang Li
The polymer N2200, with its π-conjugated backbone composed of alternating naphthalene diimide(NDI) and bithiophene(DT)units, has been widely used as an acceptor for all-polymer solar cells(all-PSCs) owing to its high electron mobility and suitable ionization potential and electron affinity. Here, we developed two naphthalene diimide derivatives by modifying the molecular geometry of N2200 through the incorporation of a truxene unit as the core and NDI-DTas the branches. These starburst polymers exhibited absorption spectra and molecular orbital energy levels that were comparable to N2200. These copolymers were paired with the wide-bandgap polymer donor PTz BI-O to fabricate all-polymer solar cells(all-PSCs), which displayed impressive power conversion efficiencies up to 8.00%. The improved photovoltaic performances of all-PSCs based on these newly developed starburst acceptors can be ascribed to the combination of increased charge carrier mobilities, reduced bimolecular recombination, and formation of more favorable film morphology. These findings demonstrate that the construction of starburst polymer acceptors is a feasible strategy for the fabrication of high-performance all-PSCs.
Kang LiRuihao XieWenkai ZhongKaiwen LinLei YingFei HuangYong Cao
Photovoltaic performance of the organic solar cells （OSCs） based on 2-（（5＇-（4-（（4-（（E）-2-（5＇-（2,2-dicyanovinyl）-3＇,4-dihexyl- 2,2＇-bithiophen-5-yl）vinyl） phenyl）（phenyl）amino）styryl）-4~4＇-dihexyl-2,2＇-bithiophen-5-yl）methylene）malononitrile （L（TPA- bTV-DCN）） as donor and PC70BM as acceptor was optimized using 0.25 vol% high boiling point solvent additive of 1-chloronaphthalene （CN）, 1,6-hexanedithiol （HDT）, or 1,8-diodooctane （DIO）. The optimized OSC based on L（TPA-bTV- DCN）-PC70BM （1：2, w/w） with 0.25 vol% CN exhibits an enhanced power conversion efficiency （PCE） of 2.61%, with Voc of 0.87 V, Jsc of 6.95 mA/cm2, and FF of 43.2%, under the illumination of 100 mW/cm2 AM 1.5 G simulated solar light, whereas the PCE of the OSC based on the same active layer without additive is only 1.79%. The effect of the additive on absorption spectra and the atomic force microscopy images of L（TPA-bTV-DCN）-PCv0BM blend films were further investigated. The improved efficiency of the device could be ascribed to the enhanced absorption and optimized domain size in the L（TPA-bTV-DCN）-PC70BM blend film.
Three small molecules with the same arms and different cores of perylene diimide(PDI)or indaceno[2,1-b:6,5-b']dithiophene(IDT)were designed and synthesized as the acceptor materials for P3HT-based bulk-heterojunction(BHJ)solar cells.The impacts of the different cores on the optical absorption,electrochemical properties,electron mobility,film morphology,photoluminescene characteristics,and solar cell performance were thoroughly studied.The three compounds possess a broad absorption covering the wavelength range of 400–700 nm and relatively low lowest unoccupied molecular orbital(LUMO)energy levels of?3.86,?3.81 and?3.99 eV.The highest power conversion efficiency of 0.82%was achieved for the BHJ solar cells based on SM3 as the acceptor material,the compound with a PDI core.
LIU XinCAI PingCHEN DongChenCHEN JunWuSU ShiJianCAO Yong
We present here a series of perylene diimide(PDI)based isomeric conjugated polymers for the application as efficient electron acceptors in all-polymer solar cells(all-PSCs).By copolymerizing PDI monomers with 1,4-diethynylbenzene(para-linkage)and 1,3-diethynylbenzene(meta-linkage),isomeric PDI based conjugated polymers with parallel and non-parallel PDI units inside backbones were obtained.It was found that para-linked conjugated polymer(PA)showed better solubility,strongerπ-πstacking,more favorable blend morphology,and better photovoltaic performance than those of meta-linked conjugated polymers(PM)did.Device based on PTB7-Th:PA(PTB7-Th:poly{4,8-bis[5-(2-ethylhexyl)-thiophen-2-yl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)-carbonyl]thieno[3,4-b]thiophene-4,6-diyl})showed significantly enhanced photovoltaic performance than that of PTB7-Th:MA(3.29%versus 0.92%).Moreover,the photovoltaic performance of these polymeric acceptors could be further improved via a terpolymeric strategy.By copolymerizing a small amount of meta-linkages into PA,the optimized terpolymeric acceptors enabled to enhance photovoltaic performance with improved the short-circuit current density(Jsc)and fill factor(FF),resulting in an improved power conversion efficiency(PCE)of 4.03%.
Xiao-Cheng LiuQing-Wu YinZhi-Cheng HuZhen-Feng WangFei HuangYong Cao
设计合成了Por-N,Por-NBr,Por-Cu-N和Por-Cu-NBr四种水醇溶性小分子卟啉衍生物.对这类卟啉小分子衍生物的紫外可见吸收光谱研究表明,基于金属铜配位的卟啉小分子衍生物较未配位化合物有微弱的蓝移.循环伏安法对这类小分子卟啉衍生物的研究表明,基于金属铜配合物的卟啉衍生物的最高占有分子轨道能级均没有明显变化.采用空间电荷限制电流方法对小分子卟啉衍生物的研究表明,基于金属铜配位的卟啉小分子衍生物的电子迁移率得到明显提高.以聚合物PCE10为给体材料,富勒烯衍生物PC71BM为受体材料,以及合成的小分子卟啉衍生物为阴极界面层制备了结构为ITO/PEDOT:PSS/PCE10:PC71BM/卟啉小分子衍生物/Al的聚合物太阳电池器件.器件研究结果表明,化合物Por-NBr,Por-Cu-N与Por-Cu-NBr作为电子传输层的器件的光电转换效率达到9%以上,其中以Por-Cu-N作为阴极界面层的器件达到的最高效率为9.12%,相应器件的短路电流密度,开路电压以及填充因子分别为16.91 m A·cm-2,0.79 V和68.1%.表明这类水醇溶性小分子卟啉衍生物作为聚合物太阳电池的阴极界面层有着广阔的应用前景.
In this work, photovoltaic properties of the PBDB-T:ITIC based-NF-PSCs were fully optimized and characterized by tuning the morphology of the active layers and changing the device architecture. First, donor/acceptor(D/A) weight ratios were scanned,and then further optimization was performed by using different additives, i.e. 1,8-diiodooctane(DIO), diphenyl ether(DPE),1-chloronaphthalene(CN) and N-methyl-2-pyrrolidone(NMP), on the basis of best D/A ratio(1:1, w/w), respectively. Finally,the conventional or inverted device architectures with different buffer layers were employed to fabricate NF-PSC devices, and meanwhile, the morphology of the active layers was further optimized by controlling annealing temperature and time. As a result,a record efficiency of 11.3% was achieved, which is the highest result for NF-PSCs. It's also remarkable that the inverted NF-PSCs exhibited long-term stability, i.e. the best-performing devices maintain 83% of their initial PCEs after over 4000 h storage.
