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

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