Berlin 2018 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 45: Organic photovoltaics and electronics
HL 45.7: Talk
Thursday, March 15, 2018, 16:45–17:00, EW 203
Ideality and Charge Transfer State Characteristics of “Real” Organic Solar Cells — •Clemens Göhler and Carsten Deibel — Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz, Germany
Organic solar cells show promising progress by using the concept of a charge transfer (CT) state, but still trail their inorganic and hybrid counterparts in efficiency. One of the reasons might lie in the comparably high recombination of charge carriers, as numerous studies found links between recombination, CT state properties, and losses in the open circuit voltage of the solar cell.
In-depth analysis of the CT state is frequently performed with external quantum efficiency (EQE) measurements in the sub-gap region, focusing on small currents resulting from direct CT excitations; and by inducing electroluminescence (EL) emission from the solar cell using an applied driving current. Recombination effects can be quantified with the ideality factor nid from the Shockely equation, usually acquired from the current–voltage (JV) characteristics of the solar cell.
Empirically, however, organic solar cells oftentimes do not represent an ideal Shockley diode, but should better be treated with regard to shunt and series resistances. Consequently, we find that even small driving currents applied during EL measurements cause significant heating of the solar cell that requires careful analysis; and that a resistance free method to obtain nid is preferable to JV measurements.