A Strategy to Obtain Long‐Term Stable Heteropoly Blues for Photosensitive Property Investigations

Abstract

which should have wide spectrum absorptions, anchoring groups, and appropriate energy levels in order to absorb more sunlight and excite the ground-state electrons to the excited state, then inject into the semiconductor conduction band, while the holes remain in the dye molecule form the charge separations, which ensure the effective regenerations of the photosensitizers and the unidirectional electron injections. [2] In recent decades, great efforts have been made to develop the photosensitizers with high stability, low-cost, and high solar energy conversion in the fields of photocatalysts and solar cells. [3,4] However, developing broad-spectrum photosensitizers is still a big challenge. At present, the commonly used photosensitizers including ruthenium-pyridine, porphyrin, and pure organic dyes, have efficiently improved the power conversion efficiencies (PCEs) of the DSSCs. [5] However, their large-scale productions and applications in photovoltaic industry have been limited by their high costs and the cumbersome process in the synthesis and purification of photosensitizers. [6] Furthermore, the defects of some photosensitizers in spectral absorption also restrict the utilization of sunlight. So, it is urgent to develop the photosensitizers with environment-friendly, simple preparations, low costs, and wide spectra absorptions.Heteropoly blues (HPBs) is a reductive state of polyoxometalates (POMs representing oxidation state) with fascinating structures, abundant element compositions, reversible redox properties, and wide pH stability. [7,8] The advantages of HPBs as photosensitizer are as follows: i) their wide and strong spectral absorptions in visible and near-IR regions; ii) the anchoring groups are easily to coordinated to HPBs to firmly adsorb on the semiconductor surface; iii) their energy levels involving the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) can be adjusted by the composition, structure, and charge density to ensure the effective unidirectional electron injections and photosensitizer regenerations; [9] iv) their excellent light, thermal and electrochemical stability, their ability to accept or lose "blue" electrons without any structural transformations. As a kind of the potential photosensitizer candidates, HPBs have been increasingly recognized in terms of photocatalysis and solar cells. [10][11][12][13][14] However, the instability of HPBs in the air restricts the further research of their photosensitivity and their use as the photosensitizers in DSSCs.The photosensitizer is the soul of dye-sensitized solar cells (DSSCs), i.e., the key factor influencing the performance of DSSCs. The commonly used photo sensitizers are expensive carboxylic pyridine ruthenium-based complexes, so it is urgent to develop low-cost photosensitizers. Heteropoly blues (HPBs) could be a kind of excellent photosensitizers due to their wide spectra absorption; however, most of them are hardly stable in the air. Here, a strategy of combining the improved vacuum...

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