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In recent years,commercial cell technologies have progressively adopted many of the high efficiency attributes previously only found in laboratory cells such as selective emitters,well passivated front and rear surfaces and localised low-area rear metal contacts.As a result of such improvements and corresponding reductions in recombination mechanisms,wafer quality contributes increasingly to determining achievable efficiencies,with many companies turning to the use of high quality n-type monocrystalline silicon for their highest efficiency products to avoid the limitations imposed by the standard industrial p-type wafers.Examples of such companies include SunPower,Panasonic,Solevo,Yingli,LG and TetraSun.An alternative approach to achieving high efficiency is to apply new defect passivation technology to the standard p-type wafers to achieve similar minority carrier lifetimes as found in n-type wafers and FZ material with the corresponding potential to achieve open circuit voltages in excess of 700mV and efficiencies approaching 23%.Of particular importance in the defect passivation processes is the control of the hydrogen charge state which in turn determines its reactivity and mobility within the silicon.Also of importance is the ability to trap the hydrogen within the silicon and stabilise the passivation during thermal processing of devices and particularly during cool-down following thermal treatments.Methods for achieving such enhanced defect passivation will be presented along with the underlying theory associated with the manipulation and control of the hydrogen and its reactivity.