Hybrid metal halide perovskites have emerged as a potential photovoltaic material for low-cost thin film solar cells due to their excellent optoelectronic properties. However, high efficiencies obtained with lab-scale cells are difficult to replicate in large modules. The upscaling process requires careful optimization of multiple steps, such as laser scribing, which divides a module into serially connected cells using a pulsed laser beam. In this work, we characterize the effect of laser scribing on the perovskite layer adjacent to a P3 scribe line using analytical scanning and cross-sectional transmission electron microscopy techniques. We demonstrate that lateral flow of residual thermal energy from picosecond laser pulses decomposes the perovskite layer over extended length scales. We propose that the exact nature of the change in perovskite composition is determined by the presence of preexisting PbI2 grains and hence by the original perovskite formation reaction. Furthermore, we show that along the P3 lines, the indium tin oxide contact is also damaged by high-fluence pulses. Our results provide a deeper understanding on the interaction between laser pulses and perovskite solar modules, highlighting the need to minimize material damage by careful tuning of both laser parameters and the device fabrication procedure.