Shown above is the probe station and associated electronics for the admittance measurement system. Two Kelvin probes are manipulated to make contact to small test solar cells placed on the sample stage (to right). The probes allow for separate current and voltage contacts to the cell. The two voltage probes are fed to the differential input of a PAR model 113 low noise broadband amplifier (dc-100 kHz). The output of the amplifier is fed out of the shielded room both to Channel 1 of the Keithley 199 dmm (for measuring the dc bias) and to Channel 1 of the HP-3562a analyzer (for admittance measurements). One of the two current probes is attached to ground through a current-to-voltage conversion circuit (bandwidth dc-100 kHz). The voltage output of the I-to-V converter is fed both to Channel 2 of the Keithley dmm (for dc measurements) and, after further amplification by a second PAR-113 amplifier, to Channel 1 of the HP-3562a analyzer (for admittance measurement). The second current probe is fed from a low-impedance source which is controlled by the HP-4140b voltage source. The two dc power supplies (shown to left) are temporarily being used as the +15V and -15V supplies for the home-built op-amp circuits.
The square brass plate (top of picture) is the panel for feeding signals outside of the shielded enclosure.