Hybrid photoelectrochemical and photovoltaic cells
Appearing today in Nature Materials, Emerging Futures CEO Jeffery Greenblatt joins three other co-authors from Lawrence Berkeley National Laboratory and the Technical University of Munich to report on their development of an artificial photosynthesis system that generates hydrogen fuel and electricity at the same time. Solar cells usually have just two electrical contacts: one on the sun-facing side, and one on the back surface. Conventional solar hydrogen cells are only able to convert 6.8 percent of the photons entering the system into hydrogen fuel.
To work around the limitations of a conventional photoelectrochemical water splitting system, the team added a third electrical contact to the silicon back surface, resulting in a hybrid device. The front surface is dedicated to fuel generation, while the extra back contact allows the generated photocurrent to be split between generating solar fuel and electrical power. For example, a hybrid device made of bismuth vanadate and silicon can reach a combined (hydrogen plus electrical) efficiency of 20.2 percent, three times better than conventional solar hydrogen cells. After running simulations predicting the functionality of the device, the team built a working prototype confirming the efficacy of their theory.
Greenblatt provided the life cycle energy estimates for the analysis. He calculated that the energy return on energy investment, a common sustainability metric, could increase by a factor of between 2.0 and 7.6 for the hybrid device as compared with a conventional non-hybrid water splitting system. Thus, over its lifetime, the device can produce many times more energy—and far more than in non-hybrid systems—than was required to fabricate and operate it.