The work function is a fundamental materials parameter which strongly influences energy level alignment in heterostructures. For example, solar cell efficiency can be improved by controlling the work functions of the electron and hole extraction layers in order to better align their energy levels with those of the absorbing layer. Poly(ethylenimine) (PEI) is a polymer previously reported to reduce the work function of materials on to which it is spin coated by inducing a surface dipole. However, previous studies did not tell the whole story. In our paper we showed that the PEI can also dope a semiconductor substrate, and the band bending induced by this doping means there is a different work function reduction for p-type and n-type GaAs. We also studied the long-term degradation of the PEI in air, which relates to its other application as a carbon dioxide capture material.

• Publication: PCCP, 2019, 21, 24666-24673
• DOI: 10.1039/c9cp04490f