.. figure 18.6 in the book, as well as the entire section this occurs in. The convention you use for the sign of the biasing potential seems to be such that the potential energy shift for electrons is given by +eV. I’ve cross-checked this with a lecture video of yours where you introduced pn-junctions at Oxford in the physics C6 module and with some other literature because I was so confused. All the other literature uses the convention that the potential energy shift for electrons is -eV — and so do you in your recorded lecture. I know this is technically no mistake (and your sign convention is consistent throughout the chapter), but since it confused me very much, and since it is such an unusual convention, I just wanted to point this out because I think many other students might be similarly confused by this.
Other sources that use the convention opposite to yours are e.g. Ashcroft and Mermin, Solid State Physics, 1976, pp. 597-600, fig. 29.5; Gross and Marx, Festkörperphysik, DeGruyter, 2018, pp. 507-510, unfortunately, this latter reference is in German - they use U for V and V_D for Δφ.
I think what makes your convention confusing to me is that there is a sense in which it is only partially consistent. Namely, for the electrochemical potential of the electrons you use μ-eφ, but the energy of the electrons due to the biasing voltage is +eV. So, whereas you consistently use the same sign for both the electrostatic potential φ and the biasing voltage V, each considered on its own, the quantities as compared to each other have opposite signs.