Revealing fundamentals of charge extraction in photovoltaic devices through potentiostatic photoluminescence imaging
Lukas Wagner, Patrick Schygulla, Jan Herterich, Mohamed Elshamy, Dmitry Bogachuk, Salma Zouhair, Simone Mastroianni, Uli Würfel, Yuhang Liu, Shaik M. Zakeeruddin, Michaël Grätzel, Andreas Hinsch, Stefan W. Glunz
Abstract
The photocurrent density-voltage (J(V)) curve is the fundamental characteristic to assess opto-electronic devices, in particular solar cells. However, it only yields information on the performance integrated over the entire active device area. Here, a method to determine spatially resolved photocurrent images by voltage-dependent photoluminescence microscopy is derived from basic principles. The opportunities and limitations of the approach are studied by the investigation of III-V and perovskite solar cells. This approach allows the real-time assessment of the microscopically resolved local J(V) curve and the steady-state Jsc as well as transient effects. In addition, the measurement contains information on local charge extraction and interfacial recombination. This facilitates the identification of regions of non-ideal charge extraction and enables linking these to the processing conditions. The proposed technique highlights that, combined with potentiostatic measurements, luminescence microscopy can be a powerful tool for the assessment of performance losses and the improvement of solar cells.