CELIV (Charge Extraction by Linearly Increasing Voltage) is a powerful method that allows to study charge transport and recombination in various semiconductors. It is a complimentary technique in the sense that materials can be studied in thin films with (solar cell) stack structure, where other techniques such as Time-of-Flight (TOF) experiments are inapplicable. Two types of CELIV experiments can be performed:
1) extraction of carriers generated at equilibrium (e.g., due to doping);
2) Extraction of photogenerated carriers (photo-CELIV).
The latter mode is used for undoped films, when almost no thermally generated (equilibrium) carriers exist. Typically, photo-CELIV is used to measure the charge carrier mobility in organic semiconductors. Here, only few thermally generated carriers exist due to the large bandgap (typically 2 eV).
The measurement procedure is two-stage: a LASER pulse excites excess charge carriers within the photoactive layer which are extracted by the linearly increasing voltage. The peak extraction time of charge carriers is measured to calculate the mobilties.