A non-destructive method to infer the bulk lifetime in high-quality silicon wafers

The bulk lifetime (τ bulk ) of high-quality silicon wafers is becoming ever more important as the efficiency of the solar cells increases (i.e. >27 %). As such there is a growing necessity to measure τ bulk directly. In this work, we showcase a non-destructive technique to infer τ bulk of high-quality wafers, termed the Charge Decoupling Method. This method is very simple and only requires atomic layer deposited (ALD) aluminium oxide (Al 2 O 3 )—or any other highly charged film (e.g. >10 12 q cm −2 )—and corona charging. By measuring the decay in the effective lifetime as the net negative charge decreases—due to the sequential deposition of positive corona charges—we can quantify the shape of the curve—analogous to the fill factor for a solar cell—and from this, determine the injection-dependent τ bulk and surface recombination velocity S . To experimentally verify the method, we apply the charge decoupling method to Al 2 O 3 passivated Czochralski-grown 5 Ω cm, n -type, 150 μm thick silicon wafers. From this we obtain a τ bulk of ∼30 ms and a corresponding S of 0.2 cm −1 at an injection level of ∼10 15 cm −3 . Mathematically, we demonstrate that the charge decoupling method depends solely on the ratio of surface to bulk recombination and thus does not depend on the doping type, resistivity, charge density, wafer thickness, interface defect density and the injection-dependent bulk lifetime. • We showcase a method to infer the bulk lifetime of high-quality silicon wafers, termed the Charge Decoupling Method (CDM). • The method only requires a non-leaky dielectric layer and corona charging. • We measure a bulk lifetime of ∼30 ms (at Δ n = 10 15 cm −3 ) on Cz, 5 Ω cm, n -type, 150 μm thick silicon wafers. • Mathematically, we demonstrate that CDM depends solely on the ratio of surface to bulk recombination. • The CDM method can be used without calibrating the corona charger from time to deposited charge.