a metal-insulator-semiconductor structure was used to study the effect of hydrogen plasma treatment of solar cells. cells were fabricated on single-crystal p-type silicon and treated in hydrogen plasma for different exposure times. this causes a noticeable drop in the photocurrent and density of charge carriers with exposure time. this in turn leads to a drop in the solar cell efficiency other cells were fabricated on damaged p-type silicon, where dislocations were created by lapping the silicon surface. such a procedure simulates controllably the effect of dislocations and grain boundaries. the damaged silicon was then exposed to hydrogen plasma and an overall improvement in the performance of the solar cell was found. however over-exposure led to degradation as with single-crystal material. it is concluded that hydrogen plasma exposure has both beneficial and degrading effects. it improves solar cell characteristics when they have been degraded by dislocations, but it degrades cells by interacting with acceptors in the p-silicon. further studies are needed to attain the best compromise and to optimize solar cells made from low quality silicon