Comments on Formation of a PN-Junction

Can someone please tell me, what makes excess electrons from n-type to try to diffuse to p-type?
What is that force? It is not electrical, because even thou there is excess electrons in n-type, n-type as a whole is electrically neutral. Then what is that force?
First year electrical student :), tnx

i feel there is error in above animation, P doped semiconductor is shown with negative and N side is shown positive majority carriers..pls check