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
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.
A methanol-soluble diamine-modified fullerene derivative(denoted as PCBDANI)was applied as an efficient cathode buffer layer(CBL)in planar p-i-n perovskite solar cells(pero-SCs)based on the CH_3NH_3PbI_(3-x)Cl_x absorber.The device with PCBDANI single CBL exhibited significantly improved performance with a power conversion efficiency(PCE)of 15.45%,which is approximately17%higher than that of the control device without the CBL.The dramatic improvement in PCE can be attributed to the formation of an interfacial dipole at the PCBM/Al interface originating from the amine functional group and the suppression of interfacial recombinationby the PCBDANI interlayer.To further improve the PCE of pero-SCs,PCBDANI/LiF double CBLs were introduced between PCBM and the top Al electrode.An impressive PCE of 15.71%was achieved,which is somewhat higher than that of the devices with LiF or PCBDANI single CBL.Besides the PCE,the long-term stability of the device with PCBDANI/LiF double CBLs is also superior to that of the device with LiF single CBL.
In this study,two fullerenes(C60,C70)and their methano-substitutions(PC61BM,PC71BM),as electron transport materials(ETMs)in perovskite solar cells(Pero-SCs),were systematically studied.As being used as ETMs,methanofullerenes,though with lower electron mobility compared to the counterpart pristine fullerenes,lead to higher power conversion efficiencies(PCEs)of Pero-SCs.The difference is likely caused by the fill-out vacancies and smoother morphology of the interfaces between ETM and perovskite layers,as they were prepared by different methods.In addition,compared to C60 and PC61BM,C70 and PC71BM showed priority in terms of short-circuit current density,which should be attributed to fast free charge extraction abilities.
Kaicheng ZhangHao YuXiaodong LiuQingqing DongZhaowei WangYaofeng WangNing ChenYi ZhouBo Song
Though the power conversion efficiencies（PCEs） of organic solar cells（OSCs） have been boosted to 12%,the use of highly pollutive halogenated solvents as the processing solvent significantly hinders the mass production of OSCs. It is thus necessary to achieve high-efficiency OSCs by utilizing the halogen-free and environmentally-friendly solvents. Herein, we applied a halogen-free solvent system（oxylene/1-phenylnaphthalene, XY/PN） for fabricating fullerene-free OSCs, and a high PCE of 11.6% with a notable fill factor（FF） of 72% was achieved based on the PBDB-T：IT-M blend, which is among the top efficiencies of halogen-free solvent processed OSCs. In addition, the influence of different halogen-free solvent additives on the blend morphology and device performance metrics was studied by synchrotron-based tools and other complementary methods. Morphological results indicate the highly ordered molecular packing and highest average domain purity obtained in the blend films prepared by using XY/PN co-solvent are favorable for achieving increased FFs and thus higher PCEs in the devices.Moreover, a lower interaction parameter（χ） of the IT-M：PN pair provides a good explanation for the more favorable morphology and performance in devices with PN as the solvent additive, relative to those with diphenyl ether and Nmethylpyrrolidone. Our study demonstrates that carefully screening the non-halogenated solvent additive plays a vital role in realizing the efficient and environmentally-friendly solvent processed OSCs.
