Session BC33 - Novel Surface Probes.
ORAL session, Sunday afternoon, March 21
Room 162W, GWCC
Electrostatic force microscopy (EFM) is used to study the surface contact potential (V_s) of Cu(In,Ga)Se_2 (CIGS) thin film solar cells and n-type indium tin oxide (ITO) thin films. The solar cells were made by depositing first a n-type layer of CdS and then a n-type layer of ZnO on top of p-type CIGS to form the p-n junction. EFM is done on the ZnO surface. The surface of these samples contain grains of approximate 0.5 \mum size. These small grains coalesce into large grains of about 10 \mum. For the solar cells, we find that the surface contact potential at the grain boundaries is 120-250 mV higher than on the grains. Some grains show lower surface contact potentials, by as much as 250 mV. The ITO thin films have smaller grains (12-30 nm diameter) and smoother surface, the surface contact potential at the grain boundaries is 35-50 mV higher than on the grains. In addition to small grains, one ITO sample also has some larger grains (40-70 nm), the V_s difference between these larger grains and their boundaries is around 100 mV. We will discuss the implication of our findings on device performance.