penghuang

A series of star-shaped small molecular cathode interlayer materials are synthesized for PTB7:PC₇₁BM based polymer solar cells (PSCs), comprising neutral amino groups, quaternary ammonium ions, amino N-oxides, and sulfobetaine ions as pendant polar functionalities, respectively. For the first time, the effect of these different pendant functional groups with or without mobile counterions on the cells' photovoltaic properties is investigated in detail. A large improvement in device performance is observed by inserting these cathode interfacial layers (CILs) between the PTB7:PC₇₁BM active layer and the Al electrode. The CILs could effectively lower the work function of the Al cathode, increase the built-in potential, and decrease the series resistance of the related PSCs. poly(9,9-dioctylfluorene-co-N-[4-(3-methyl-propyl)]-diphenylamine) with pendant quaternary ammonium ions shows the best cathode modification ability, giving rise to the highest power conversion efficiency of 10.1%, even better than that of the typical poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] based device. The design strategy and structure–property relationships concluded in this work will be helpful to develop more efficient cathode interface materials for high-performance PSCs in the future.

A series of star-shaped small molecular cathode interlayer materials with variable pendant polar functionalities are designed for polymer solar cells. For the first time, the effect of different pendant functional groups with/without mobile counterions on the cell's photovoltaic properties is investigated. Poly(9,9-dioctylfluorene-co-N-[4-(3-methyl-propyl)]-diphenylamine) with pendant quaternary ammonium ions (TFB) shows the best cathode modification capability, achieving an efficiency of 10.1%.

The preparation of solar-cell-grade Cu₂ZnSnS₄ (CZTS) thin films from ligand-capped small-grained CZTS particles remains hindered by problems of phase segregation, composition non-uniformity, and in particular carbon-layer formation. Herein, through a systematic comparative study of annealed films of CZTS nanocrystals prepared using conventional oleylamine and those prepared using formamide, these problems are found to be mainly attributable to the influence of the ligands, and mechanisms are proposed. Importantly, the origin of the carbon layer in oleylamine-capped CZTS films is revealed to be the reaction between oleylamine and sulfur. This carbon layer has a very poor electrical conductivity, which can be the reason for the limited performance of such films. Fortunately, these problems can almost all be avoided by replacing oleylamine with formamide to form CZTS films.

Grains on film: Carbon-rich ligands are responsible for phase segregation, composition non-uniformity, and carbon-layer formation in carbon-rich Cu₂ZnSnS₄ films. Particularly, the carbon layer is a consequence of the reaction between oleylamine and sulfur, and mechanisms are proposed. The carbon layer has very poor electrical conductivity. The problems above are greatly reduced in carbon-poor Cu₂ZnSnS₄ films.

Herein, we report a tailored Ag mesh electrode coated with poly(3,4-ethylenedioxythiophene) (PEDOT) polymer on a flexible polyethylene terephthalate (PET) substrate. The introduction of this highly conductive polymer solves the existing problems of Ag mesh-type transparent conductive electrodes, such as high pitch, roughness, current inhomogeneity, and adhesion problems between the Ag mesh grid and PEDOT polymer or PET substrate, to result in excellent electron spreading from the discrete Ag mesh onto the entire surface without sacrificing sheet conductivity and optical transparency. Based on this hybrid anode, we demonstrate highly efficient flexible polymer solar cells (PSCs) with a high fill factor of 67.11 %, which results in a power conversion efficiency (PCE) of 6.9 % based on a poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′] dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophenediyl}):[6,6]-phenyl-C₇₁-butyric acid methyl ester bulk heterojunction device. Furthermore, the PSC device with the Ag mesh electrode also exhibits a good mechanical bending stability, as indicated by a 70 % retention of the initial PCE after 500 bending cycles compared with the PSC device with a PET/indium tin oxide electrode, which retained 0 % of the initial PCE after 300 bending cycles.

Highly conductive, flexible hybrid electrode: Herein, we report a highly conductive, flexible hybrid Ag mesh electrode on a flexible polyethylene terephthalate (PET) substrate. The introduction of a highly conductive polymer solves the existing problems of Ag mesh-type transparent conductive electrodes, and highly efficient flexible polymer solar cells (PSCs) are demonstrated.