Before we have a look at the solutions, let us have a look at what causes iPhone 6 black screen of death issue.
Insufficient battery - Most of the times, when the screen goes black or when your device won't turn on, it is due to battery issues. If the battery of your device is low or if it damaged, then chances are high that this issue may occur.
Storage damaged - Memory of your device also gets a say in this situation. If your device is running low of memory or if there are too many apps, then this issue might occur. Running too many apps on a low memory can cause damage to the storage.
System glitches - Errors in the operating system can also be one of the reasons that might cause this issue. This can take place while updating the software or while updating a certain app.
Hardware problem - In addition to all the above mentioned reasons, hardware also plays an important role in the occurrence of this issue. Sometimes it might be a damaged screen or any other component that causes this issue.