High sensitivity Hall effect system capable of measuring wide range of sample resistance, carrier density, mobility and temperature is critically needed for development of many advanced electronics material. We recently developed a high-sensitivity variable temperature Hall measurement system based on rotating parallel dipole line (PDL) magnet. The PDL system is an emerging AC field Hall system that has played a key role in the recent discovery of carrier-resolved-photo Hall effect . This variable temperature Hall system allows us to study the mobility scattering mechanism and extracting the donor or acceptor level of the material. We demonstrated these applications in several high-interest materials such as high performance kesterite (CZTS) and perovskite solar absorber films. For example, we extracted the CZTS acceptor level of 210 meV, very close to the theoretical prediction of 217 meV level associated with CuZn antisite acceptor level.  O. Gunawan et. al., Nature 575, 151 (2019).