Benzothiadiazole-based hole transport materials for high-efficiency dopant-free perovskite solar cells: Molecular planarity effect

A new benzothiadiazole-based D-A-D hole transport material(DTBT)has been designed and synthesized with a more planar structure by introducing of thiophene bridges.The results indicate a lower band gap and quite higher hole mobility for the DTBT.Furthermore,the enhancement in molecular planarity with simple thiophene unit increases the hole mobility of DTBT(8.77×10^-4cm^2 V^-1s^-1)by about 40%.And when DTBT is used as hole transport material in perovskite solar cells,the photoelectric conversion efficiency of the corresponding dopant-free devices is also significantly improved compared with that of the conventional BT model molecule without thiophene.In terms of device stability,DTBT-based devices show a favorable long-term stability,which keep 83%initial efficiency after 15 days.Therefore,the introducing of thiophene bridges in D-A-D typed HTMs can improve the molecular planarity effectively,thereby increasing the hole mobility and improving device performance.

Heteroatom engineering on spiro-type hole transporting materials for perovskite solar cells

A series of spiro-type hole transporting materials, spiro-OMe TAD, spiro-SMe TAD and spiro-OSMe TAD,with methoxy, methylsulfanyl or half methoxy and half methylsulfanyl terminal groups are designed and prepared. The impact of varied terminal groups on bulk properties, such as photophysical, electrochemical, thermal, hole extraction, and photovoltaic performance in perovskite solar cells is investigated.It is noted that the terminal groups of the hole transporting material with half methoxy and half methylsulfanyl exhibit a better device performance and decreased hysteresis compared with all methoxy or methylsulfanyl counterparts due to better film-forming ability and improved hole extraction capability.Promisingly, the spiro-OSMe TAD also shows comparable performance than high-purity commercial spiro-OMe TAD. Moreover, the highest power conversion efficiency of the optimized device employing spiro-OSMe TAD exceeding 20% has been achieved.

C≡N-based carbazole-arylamine hole transporting materials for perovskite solar cells: Substitution position matters

Hole transporting materials(HTMs)containing passivating groups for perovskite materials have attracted much attention for efficient and stable perovskite solar cells(PSCs).Among them,C≡N-based molecules have been proved as efficient HTMs.Herein,a series of novel C≡N functionalized carbazole-arylamine derivatives with variable C≡N substitution positions(para,meta,and ortho)on benzene-carbazole skeleton(on the adjacent benzene of carbazole)were synthesized(p-HTM,m-HTM and o-HTM).The experimental results exhibit that the substitution positions of the Ctriple bondN unit on HTMs have minor difference on the HOMO energy level and hydrophobicity.m-HTM has a relatively lower glass transition temperature compared with that of p-HTM and o-HTM.The functional theory calculations show that the C≡N located on meta position exposed very well,and the exposure direction is also the same with the methoxy.Upon applying these molecules as HTMs in PSCs,their device performance is found to sensitively depend on the substitution position of the C≡N unit on the molecule skeleton.The devices using m-HTM and o-HTM exhibit better performance than that of p-HTM.Moreover,m-HTM-based devices exhibit better light-soaking performance and long-term stability,which could be resulted from better interaction with the perovskite according to DFT results.Moreover,we further prepared a HTM with two C≡N units on the symmetrical meta position of molecular skeleton(2m-HTM).Interestingly,2m-HTM-based devices exhibit relatively inferior performance compared with that of the m-HTM,which could be resulted from weak negative electrical character of C≡N unit on 2m-HTM.The results give some new insights for designing ideal HTM for efficient and stable PSCs.

Pyridine-triphenylamine hole transport material for inverted perovskite solar cells

In the light of superior interaction between pyridine unit and perovskite,a facile star-shaped triphenylamine-based hole transport material(HTM)incorporating pyridine core(coded as H-Pyr)is designed and synthesized.A reference HTM with benzene core,coded as H-Ben,is also prepared for a comparative study.The effects of varying core on HTMs are investigated by comparing the photophysical,electrochemical and hole mobility properties.It is found that pyridine core exhibits better conjunction and decreased dihedral angles with triphenylamine side arms than that of benzene,leading to obviously better hole mobility and well-matched work function.The perovskite film prepared on H-Pyr also shows improved crystallization than on H-Ben.Photoluminescence and electrochemical impedance studies indicate improved charge extraction and reduced recombination in the H-Pyr-based perovskite solar cells.Consequently,H-Pyr-based device exhibits higher efficiency than H-Ben-based one.After doping with a Lewis acid,tris(pentafluorophenyl)borane,H-Pyr-based device delivers a champion efficiency of 17.09%,which is much higher compared with 12.14% of the device employing conventional poly(3,4-ethy lenedioxythiophene)polystyrene sulfonate(PEDOT:PSS)as HTM.Moreover,the H-Pyr-based device displays good long-term stability that the power conversion efficiency remains over 80% of the initial value after storage in ambient(relative humidity=50±5%)for 20 days.

丙二醇电解液键结构调控及其水系锌离子电池稳定性研究

水系锌基电池具有低成本和高安全性的优点,是很有潜力的储能技术.然而,枝晶、副反应和较差的低温性能限制了其实际应用,这与电解液的溶液组成密切相关.在本工作中,我们通过调控丙二醇电解液的溶剂结构及键相互作用,有效抑制了锌枝晶和副反应.丙二醇具有较高的电子云密度和DN(Donor number)值,可以破坏水分子间和水分子与Zn^(2+)间的相互作用,从而提高H–O共价键的强度,降低水活性和冰点,改变Zn^(2+)的溶剂化结构.制备的电池器件表现出高的循环稳定性(Zn//Zn电池循环超过1000 h),高可逆性(库伦效率达到98.9%),高储锌性能(在5 Ag^(-1)下比容量为225 mA h g^(-1),循环5000圈容量保持率为92.6%)和优异的防冻性能(在-20℃下循环500圈比容量为190 mA h g^(-1)).本工作为高性能水系锌离子电池的发展提供了一种有前景的策略.