The past three years have seen the rapid emergence and development of a new solar cell technology based on organic-inorganic halide perovskites with energy conversion efficiency reaching a confirmed 20.1% at year-end. There remain challenges to be addressed for the commercialisation of such technology such as stability, integration into monolithic tandem devices, replacement of lead, and development of large area devices. Additionally, it is imperative to develop standard, reliable and fast characterisation techniques for rapid identification of defects at each step during the perovskite solar cell (PSC) processing and fabrication. Electroluminescence (EL) and photoluminescence (PL) imaging have been widely used as standard techniques for silicon solar cell technology in commercial production and research laboratories. Not only are such imaging techniques useful in revealing process-induced defects, they also allow spatial mapping of key electrical parameters, such as series resistance and diode saturation current amongst others. The use of such imaging techniques for macroscopic-scale full device characterization is yet to be developed for PSCs although valuable works have been done investigating optical and electrical properties of perovskites via time-resolved PL and recently micro-scale PL mapping.

In the present study, we first validate the Planck’s generalized emission law that correlates the voltage and the emitted luminescence by both PL and EL measurements, for a 10 × 10 mm² PSC. This finding enables quantitative analysis of luminescence data and is the basis for further analysis of a wide range of essential electrical parameters as outlined above. PL images under open-circuit condition provide useful information on the regions of the device suffering from high non-radiative recombination (i.e. lower local voltages; darker regions). It is noteworthy that contactless PL imaging can provide information on implied open-circuit voltages of the devices, which provides a rapid and non-destructive approach for identifying process-induced defects prior to the completion of a full device. By comparing PL images with EL images, the series resistance distribution in the device can be determined. Moreover, PL imaging performed under short-circuit condition allows the visualization of high series resistance regions. Light-induced effects on thin films and full devices (e.g. after prolonged current density-voltage measurements) also revealed perturbed regions as a result of ion migration. The use of luminescence imaging under various illumination intensities and/or applied biases characterising the full area of a PSC can enhance our understanding of hysteresis, electric field distribution and ion migration valuable for the design and process optimisation so to improve the performance of PSCs.