Perovskite solar cells have shown a significantly increased single-cell efficiency of 25.7% in the last decade from just 3.8% in 2008 [1] [2]. The upcoming challenges are stability and ensuring the required lifetime expected of photovoltaic technology deployed in the field. One such critical criterion is the response to partial shading created on a panel due to the surrounding environment, like trees, buildings, or even dust and leaves on the panel. Therefore, it is critical to understand the response of perovskites to shading to support the scaling up of the technology.

Shading tests were performed on perovskite mini-modules with four cells monolithically connected in a series configuration in this work. The shading was executed parallel and perpendicular to the laser scribes. In the perpendicular direction, the shading covers the cells equally, whereas parallel shading covers individual cells completely. The shading in the perpendicular direction did not reveal degradation after shading. However, the parallel direction showed degradation. It is due to the difference in the current generated in the different cells due to the partial shading. The shaded cell begins to operate in a reverse voltage, and when the voltage across the cell is larger than the breakdown voltage, the module degrades. It confirmed the low breakdown voltage of PSCs reported in other studies in recent years [3] [4] [5].

A reverse I-V scan of the mini-module revealed a low breakdown voltage of about -1.6V for a cell. Other tests provided a deeper insight into the reverse bias degradation mechanism. An Electroluminescence test helped visualize the degradation of the module, which showed a dark spot in the shaded cell. Also, the ability of the module to recover after degradation under light soaking was tested. The open circuit voltage recovered partially to about 2.5V as compared to 4V before degradation, but the I-V curve showed highly shunted behavior with a poor fill factor. The parallel shading tests were conducted for semi-transparent modules which utilize Indium Tin Oxide (ITO) as the back electrode instead of Copper, and it showed lower degradation indicating a higher breakdown voltage.

In conclusion, it was evident from this study that perovskite solar cells perform poorly under partial shading due to their low reverse breakdown voltage. Due to different combinations in the materials for the perovskite composition itself, and the different transport layers and electrodes, the exact mechanism can vary. The main reason cited in other literature studies is a combination of mobile ions in the absorber layer, metal atoms from the electrode drifting towards the perovskite layer leading to shunting, migration of iodine, and phase segregation of perovskite [4] [6] [7]. Due to the dynamic nature of the perovskite absorber layer, more extensive tests are necessary to prove its industrial relevance, especially under partial shading.