Probing individal subcells of fully printed and coated polymer tandem solar cells using multichromatic opto-electronic characterization methods

In this study, a method to opto-electronically probe the individual junctions and carrier transport across interfaces in fully printed and coated tandem polymer solar cells is described, enabling the identification of efficiency limiting printing/coating defects. The methods used are light beam induced current (LBIC) mapping, External quantum efficiency (EQE) measurements, and monochromatic current-voltage (I-V) characterization. Using these methods, inherent limitations to the accuracy of EQE and LBIC measurements on non-ideal tandem solar cells are identified and described through the use of a small-signal electrical model. The model is able to predict the EQE spectrum of the non-ideal polymer tandem solar cell, using extracted values of shunt- and series resistance of the individual junction of the tandem cell. This finally enables LBIC mapping of the individual junctions of the tandem polymer solar cells, using a combination of light and voltage-biasing.