Revealing fundamentals of charge extraction in photovoltaic devices through potentiostatic photoluminescence imaging

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 J_sc 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.