Unified lifetime metrology and photoluminescence imaging of passivation defects for silicon PV

We have recently introduced an improved QSS-mu PCD lifetime measurement with a strict quality of decay control technique. This enabled unified, parameter free determination of the decay lifetime and the steady-state lifetime over a broad steady-state injection range (up to about 30suns). Excellent correlation was found with Sinton QSSPC measurement. The advantage of spatially resolved mu PCD was applied for wafer mapping. Emitter saturation current, J(0), mapping was obtained directly from small perturbation decay lifetime using the Basore-Hansen procedure. The maps revealed commonly present passivation defects manifested as high J(0) areas. In this work we report further improvement of the approach, especially regarding speed and resolution. Our research involved photoluminescence measurements on passivated test wafers in sequence with the QSS-mu PCD unified lifetime measurement including J(0). On selected sites the value of J(0) was intentionally varied with corona charge induced field-effect. This enabled a unique PL calibration to J(0) and other recombination parameters. Quantitative characteristics enabled us to compare PL procedures for the determination of J(0) and to select a practical version for J(0) imaging that uses direct J(0) determination from the ratio of generation rate G to PL intensity. We have found that this J(0) procedure correlates well with the commonly used Kane-Swanson method. In addition, it carries the practical advantages of needing only a single PL image with a straightforward calibration and relaxed requirements regarding injection range restriction. (C) 2013 The Authors. Published by Elsevier Ltd.