Much of our research relies on determining the quality of silicon materials for photovoltaic applications. The main parameter used to characterise bulk silicon PV materials is the minority carrier lifetime. For lower cost multicrystalline materials another commonly evaluated parameter is the bulk interstitial iron concentration.
My Warwick group has three complementary technqiues available for assessing such parameters:
- Quasi-steady-state photoconductance (QSS-PC). We have a Sinton WCT-120 lifetime tester, which enables the minority carrier lifetime to be determined as a function of the excess carrier concentration. In model system this can be used in a semi-spectroscopic manner to isolate fundamental properties of recombination-active defects. This system was modified by the manufacturer to fulfil our research requirements, and has a smaller coil than standard (1cm diameter). It is also possible to make temperature-dependent measurements (room temperature to ~150°C) using our system.
- Quasi-steady-state photoluminescence (QSS-PL). Arriving in Summer 2014 will be a Sinton WCT-120PL system, which can also be used in QSS-PC mode. It can be used to determine minority carrier lifetime accurately at low levels of injection.
- Photoluminescence (PL) imaging. A BT Imaging LIS-L1 PL system was installed in November 2013. This enables material quality images of whole wafers to be acquired within seconds. Under some conditions these maps can be calibrated in terms of the carrier lifetime and bulk interstitial iron concentration.
The systems are installed in the School of Engineering at Warwick, in room A408B.
Internal or external researchers interested in using these systems for academic or industrial work on silicon PV materials should get in touch with John Murphy.
Sinton WCT-120 QSS-PC minority carrier lifetime measurement system
BT Imaging LIS-L1 PL imaging system