Given that Bristol researchers did not explain the physics behind their diamond battery we can only speculate but considering some recent developments we can make some good guesses.
In a typical configuration you have a P-N semiconductor junction placed next to beta emitter. The beta particles impact the PN junction and create electron-hole pairs that are pulled apart by the junction to produce a current.
The use of diamond seems like a could be a significant innovation:
1) Carbon-14 is an efficient beta emitter and could make op part of all of the diamond material.
2) Diamond has a wide band-gap which is necessary for high efficiency conversion to electricity.
3) Has strong resistance to radiation damage.
Considering that diamond is itself a semiconductor we could also do away with the silicon. For example diamond is being considered for highly efficient photovoltaic cells.
(see: http://exploration.vanderbilt.edu/news/news_diamond.htm)
The diamond could be stacked next to a conducting metal to create a Skottky barrier which is a type of P-N junction. The beta particles would excite the electrons with enough energy to push them over the barrier and create a current.
(see: https://en.wikipedia.org/wiki/Schottky_barrier)
It probably functions similar to a betavolatic cell. (See: https://en.wikipedia.org/wiki/Betavoltaic_device)
In a typical configuration you have a P-N semiconductor junction placed next to beta emitter. The beta particles impact the PN junction and create electron-hole pairs that are pulled apart by the junction to produce a current.
The use of diamond seems like a could be a significant innovation: 1) Carbon-14 is an efficient beta emitter and could make op part of all of the diamond material. 2) Diamond has a wide band-gap which is necessary for high efficiency conversion to electricity. 3) Has strong resistance to radiation damage.
In one configuration the diamond would be layered on top of a silicon P-N junction so it works like a conventional betavoltaic device. (see: http://large.stanford.edu/courses/2013/ph241/harrison2/)
A recent patent shows that diamond is a very efficient moderator for injecting electrons into the junction. (see https://www.google.com/patents/US9064610)
Considering that diamond is itself a semiconductor we could also do away with the silicon. For example diamond is being considered for highly efficient photovoltaic cells. (see: http://exploration.vanderbilt.edu/news/news_diamond.htm)
It is also being considered for production of next-gen schottky diodes. (see: http://www10.edacafe.com/nbc/articles/view_article.php?artic...)
The diamond could be stacked next to a conducting metal to create a Skottky barrier which is a type of P-N junction. The beta particles would excite the electrons with enough energy to push them over the barrier and create a current. (see: https://en.wikipedia.org/wiki/Schottky_barrier)