Many emerging solar absorbers are polycrystalline films with low mobility or very high resistance. This makes standard (dc) Hall measurement very difficult or impossible - yet the information of carrier density, type and mobility are critically needed to understand and optimize device performance. We have developed a high-sensitivity Hall measurement system based on a rotating parallel dipole line (PDL) magnet - a new magnetic trap system recently developed at IBM [1,2]. The system produces strong (up to 2 Tpk-pk), unidirectional and oscillating magnetic field that allows detection of small Hall signal in the Fourier domain followed by lock-in detection. We describe the experimental setup, operation characteristics and some application examples in the development of IBM high performance kesterite (CZTSSe) with device efficiency (η) up to 12%  and high performance perovskite from Korea Research Institute of Chemical Technology (KRICT, up to 19%) .