Charge Transfer Across Oriented Molecular Interfaces

Molecular 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 enhance.

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 times.

 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.