solid state physics - In the diode equation, why the exponential $exp$ and the ideality factor $n$ are there? What do they represent & what is their significance?

In the Shockley diode equation, why the exponential $\exp$ and the ideality factor $n$ are there? What do they represent & what is their significance?

I have to work on Solar Photovoltaics, and I need to understand the Shockley diode equation clearly.