Jun Shao,Songwang Yang,Lei Lei,Qipeng Cao,Yu Yu,Yan Liu
Pore size and porosity of the porous materials play an important role in catalysis, dye-sensitized solar cells and mesoscopic perovskite solar cells (PSC), etc. Increasing pore size and porosity of mesoporous TiO2 is crucial for facilitating pore-filling of perovskite, charge extraction on TiO2/CH3NH3PbI3 interface and thus cell performance enhancement. Highly porous TiO2 films (TFs) with a large pore size that extends the limit of particle size have been achieved through a novel TiO2 paste using copolymer P123 as a pore-adjusting agent and 2-butoxyethyl acetate as a solvent. A highly porous structure with the pore size of 34.2 nm and porosity of 73.5% has been obtained, the porosity of which is the largest that has ever been reported in the screen-printed TiO2 thick films. The pore size and porosity of TFs can be successively adjusted in a certain range by tuning the P123 content in the pastes. As particle size and surface area of TFs are kept almost constant, the specific investigation on the effect of varied pore size on the performance of bilayer-structured PSCs becomes possible. The hysteresis phenomenon, the notorious problem of PSCs, is found to depend greatly on pore size and porosity of TFs, that is, pore-filling of perovskite. The suppressing effect of highly porous TFs on hysteresis by avoiding charges accumulation on the interface due to enhanced interfacial contact is proved by the invariable photocurrent response after prebias treatment. A hysteresis-free solar cell with an efficiency of 15.47% was achieved by depositing a 242 nm-thick perovskite capping layer upon 350 nm-thick TF with a pore size of 34.2 nm. This method developed for the preparation of highly porous TFs provides a new way to fabricate hysteresis-free PSCs and is widely applicable for the fabrication of other mesoporous metal oxide films with large pore sizes.
Graphical Joining the dots: A core–shell–shell CdSeTe@CdS@ZnS quantum-dot-sensitized macroporous TiO 2 plate is built as a photoelectrochemical signal output system, and the film is modified further with biotin–DEVD–peptide, which can be cleaved specifically by caspase-3 and streptavidin-labeled alkaline phosphatase (SA-ALP), to assemble a multisignal-amplified photoelectrochemical platform. A macroporous TiO 2 film (M-TiO 2 ), which was prepared by burning off the polystyrene microsphere (PS) template from a PS/TiO 2 composite film, can provide a large active surface, improve electron-transport performance, and increase the photocurrent. Furthermore, core–shell–shell CdSeTe@CdS@ZnS quantum dots (QDs) were introduced to sensitize the M-TiO 2 film, which can efficiently broaden the absorption spectra range, separate and transfer charge carriers, reduce recombination loss, and improve photovoltaic response, with a sensitization shell of CdS and a passivation shell of ZnS. A multisignal-amplified photoelectrochemical platform was fabricated by further modifying this film with a combination of biotin–DEVD–peptide (Biotin–Gly–Asp–Gly–Asp–Glu–Val–Asp–Gly–Cys) (which is specifically cleaved by caspase-3) and streptavidin-labeled alkaline phosphatase (SA-ALP). Under the enzymatic catalysis of ALP with the substrate 2-phospho- L -ascorbic acid trisodium salt (AAP), ascorbic acid (AA) was generated as a better electron donor, leading to increased photocurrent output. The activity of caspase-3, which depends on the amount of residual peptide on the electrode, was inversely proportional to the amount of AA. By monitoring the variation of photocurrent caused by AA, caspase-3 activity and the therapeutic effect of nilotinib (a special medicine of chronic myeloid leukemia, CML) were indirectly detected and evaluated. The photoelectrochemical platform can be used as a potential evaluation system for monitoring caspase-3 activity and drug effects.
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