Determination of actual carrier lifetime from differential measurements
The light-biased dynamic analysis of excess carrier decay has been known to yield differential rather than actual recombination properties since 1995. This finding implies a mismatch between actual lifetime and the measured differential lifetime in the case of injection-dependent carrier lifetime. Therefore, a time-consuming integration of differential recombination properties over the entire injection range was deemed inevitable in order to obtain actual recombination properties from differential measurements. We recently observed a striking analogy to the above finding: Time-modulated luminescence measurements - notably without any additional constant bias light - feature a systematic mismatch between actual lifetime and apparent lifetime determined from the phase shift of carrier density with respect to carrier generation if lifetime is injection-dependent. This gave rise to rearrange previous findings in a quantitative theory of light-biased carrier decay, which also comprises time-modulated lifetime techniques without constant bias light. This theory directly relates measurable differential lifetime to actual carrier lifetime. It is applied in a new differential-to-actual (d2a) lifetime analysis, which allows the determination of actual carrier lifetime from differential measurements without integration over the entire injection range. In terms of practical relevance, the d2a approach brings about a drastic experimental simplification. Combined with the general advantages of dynamic lifetime techniques, it could upgrade differential carrier decay techniques and time-modulated lock-in techniques intopowerful quantitative characterization options in silicon photovoltaics. This paper provides an experimental proof ofconcept of the d2a technique based on harmonically time-modulated photoluminescence.