It has been acknowledged for over 50 years that treatments with hydrogen can improve silicon semiconductor devices. In recent years, these have been used to an advantage in silicon solar cells reducing the loss of photo-generated carriers at the silicon surface or at the silicon interface with dielectrics. However, we have found that in some types of silicon the in-diffusion of hydrogen can result in the formation of powerful recombination centers composed of carbon, oxygen, and hydrogen which reduce the carrier lifetime and ultimately the efficiency of solar cells made from such material