I fully understand the thermodynamics of ICEs and that every electric motor in a car is easily more efficient in converting power into torque.
However the efficiency of converting sun into electricity is around 35%. While driving your car carries a heavy battery of 100es of kilogramms which can only store 1/3 of energy per volume compared to eg. Diesel.
So in my calculation the net efficiency of diesel is higher.
I don't understand what measure of efficiency you are trying to use, in which Diesel would end up being better.
In environmental discussions that measure is usually something of grams-of-CO2-equivalent emitted per km. One oddity is that the usually communicated figure is only that emittted 'at the tailpipe', which is obviously zero for full electrics. Often people try to compensate by taking the kWh-per-km figure and multiplying by the CO2-per-kWh figure for their environment. This is however still misleading if compared with the tailpipe CO2 for an ICE, because the production of gasoline or diesel are also fairly CO2-intensive.
The official term of use is well-to-wheel efficiency or emissions; there is no doubt at all that electric vehicles beat ICE vehicles easily, basically on account of the ICE being relatively inefficient because of size/performance constraints.
Obviously the actually interesting figure of merit is the lifetime emissions (and the 'useful work' gained from those emissions) and while methods and tools to compute this exist computing this in a reasonable way means making a lot of assumptions (such as the miles-per-lifetime), assumptions that will be easily attacked on internet fora, and assumptions that can easily be tweaked to show what you want to show.
The reality is that (full) electric vehicles are practical and efficient for most of the population today, if not in the very near future, and that it's hard to imagine that the current dependency on oil will last very long. Ten years is a long time.
Every study that looks at total carbon emissions for a vehicle's lifespan, including manufacturing batteries for EVs and drilling/transporting the oil for ICE (whether gas or diesel) has EV coming out on top. The first year the ICE wins quite handily, but the EV chips away over time and after 3-4 years (depending on the local grid and driving habits) is a net carbon reduction.
Plus the ICE vehicle is the cleanest it will ever be on delivery day. Even with modern catalytic converters and engine management ICE vehicles will start to use more fuel and emit more particulates over its lifespan. EVs get cleaner as the green decarbonizes.
Then take into account that ICE worst case scenario for carbon emissions is around town, stop and go traffic, which is what most passenger cars spend their lives doing. It also happens to be the EV best case, since region braking makes the most out of the available energy.
However the efficiency of converting sun into electricity is around 35%. While driving your car carries a heavy battery of 100es of kilogramms which can only store 1/3 of energy per volume compared to eg. Diesel.
So in my calculation the net efficiency of diesel is higher.