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Charge Transfer Across Oriented Molecular Interfaces

semiconductors are important materials for technology applications, such as
solar cells. Current research focuses on how to organize molecules  at interfaces for more efficient energy
conversion.  Maryland MRSEC researchers
and NIST collaborators  recently showed
how the arrangement of molecules at a molecular junction impacts energy
conversion. Ultrafast electron transfer takes place when electron-donating CuPc  charge transfer, leading to more
efficient devices molecules “stand up”
on their electron-accepting C60 neighbors. Such oriented molecular interfaces


The electron
population is followed at oriented CuPc:C60 interfaces as a function of time
with two-photon photoemission.  Electrons
are first optically pumped  in the  CuPc layer, appearing as the bright red streak at short


 Upper Panel: 5 nm Thick CuPc film -  Electrons must  first diffuse through the  CuPc 
transferring  to C60 on an
800  fsec time scale. multilayer before

 Lower Panel: 1 nm Thick CuPc Film -  Electrons transfer from the single-layer ZnPc film to C60 within
150 fsec.  For this open-circuit structure, electrons
return to ZnPc at longer times,
appearing as a red horizontal streak after 1000 fsec.