Photochemical Response of Commercial MOFs: Al₂(BDC)₃ and Its Use As Active Material in Photovoltaic Devices

Abstract

The presence of organic linkers in MOFs allows introducing
\nresponse in the solid upon chemical, electrochemical, or photochemical
\nexcitation of these units. In the present study, we report the intrinsic
\nphotoresponse of four commercially available MOFs as well as after incorporation
\nof some organic guests. Laser flash photolysis measurements have
\nallowed us to detect transient species upon irradiation of commercial
\nAl2(BDC)3. The signal has been rationalized as derived from the photochemical
\ngeneration of charge separated states. In contrast to Al2(BDC)3, the
\nother three commercial MOFs tested did not exhibit any signal. The
\nphotoinduced charge separation in Al2(BDC)3 can be modulated by inclusion
\nof organic guests that can act as traps of electrons or holes increasing the
\nlifetime of charge separation. When the oxidation potential of the organic
\nguest is low, as in the case of 1,4-phenylendiamine, PDA, we have been able to observe spontaneous charge separation even for Fe-
\nBTC and Cu3(BTC)2. The basic understanding of the photoresponse has been applied to build photovoltaic cells using Al2(BDC)3
\nas semiconductor. The best performing device was the one constructed with 1,4-dimethoxybenzene, DMB, DMB@ Al2(BDC)3
\nwith the lowest thickness, which more than doubles the efficiency of the Al2(BDC)3 cells prepared without DMB.Overall, our report
\nexemplifies how understanding of the basic photochemistry can be used for developing new applications of MOFs.