Contents lists available at ScienceDirect Solar Energy Materials and Solar Cells journal homepage: www.elsevier.com/locate/solmat Light-induced lifetime degradation effects at elevated temperature in Czochralski-grown silicon beyond boron-oxygen-related degradation Michael Winter a,b,* , Dominic Walter a , Dennis Bredemeier a,b , Jan Schmidt a,b a Institute for Solar Energy Research Hamelin (ISFH), Am Ohrberg 1, 31860 Emmerthal, Germany b Department of Solar Energy, Institute of Solid-State Physics, Leibniz University Hannover, Appelstr. 2, 30167 Hannover, Germany ARTICLE INFO Keywords: LeTID Czochralski-grown silicon Boron-oxygen defect Carrier lifetime ABSTRACT The effect of ‘Light and elevated Temperature Induced Degradation’ (LeTID) of the carrier lifetime is well known from multicrystalline silicon (mc-Si) wafers and solar cells. In this contribution, we perform a series of carrier lifetime measurements to examine, whether the same effect may also be observable in boron-doped Czochralski- grown silicon (Cz-Si). The Cz-Si samples of our study are illuminated (i) at room temperature, (ii) under standard regeneration conditions eliminating the boron-oxygen (BO) related defect (i.e. at 185 °C) and (iii) at a tem- perature of 80 °C, typical for the examination of the LeTID effect in mc-Si. We observe the typical decay of the carrier lifetime due to the activation of the BO-related defect. Beyond the BO degradation, applying standard solar cell processes, there is no indication for the activation of a second defect. On samples, whose surfaces are passivated by fired hydrogen-rich silicon nitride layers, an additional bulk lifetime degradation effect on a long timescale is observed in the Cz-Si material. However, defect generation rate and injection dependence of the lifetime suggest another defect type than the mc-Si-specific LeTID defect. We conclude that by applying pro- cessing steps that trigger LeTID in mc-Si, the same defect does not occur in the Cz-Si samples examined in this study. On a long timescale, however, a hitherto unknown type of defect is activated, which is different from the mc-Si-specific LeTID defect. A careful differentiation between the various kinds of recombination centres which may form during illumination at elevated temperatures is hence of utmost importance. 1. Introduction The so-called ‘Light and elevated Temperature Induced Degradation’ (LeTID) effect [1–4] of the carrier lifetime in block-cast multicrystalline silicon (mc-Si) has become a steadily growing area of research over the last years. The firing step at the end of the solar cell production process was identified to trigger the degradation effect [4,5] and the firing peak temperature was shown to have a major impact on the extent of the lifetime degradation [6]. More recently, there have been publications indicating that a similar defect could exist in Cz-Si as well [7–9]. Other researchers, however, did not find any indications of the mc-Si-typical LeTID in Cz-Si material [10]. In addition, some pub- lications reported LeTID in other types of monocrystalline silicon ma- terials, such as Float-zone silicon and n-type Cz-Si [11–13]. In this study, we perform a series of experiments to clarify the apparent con- tradiction. We examine the carrier lifetime degradation under illumi- nation of boron-doped Cz-Si material at increased temperatures to check, if the mc-Si-specific LeTID defect also occurs in Cz-Si material. We apply various process conditions to the Cz-Si wafers known to effectively trigger LeTID in mc-Si wafers. 2. Experimental details We use standard boron-doped Cz-Si wafers with a base resistivity of 1.3 Ω cm. The saw damage of the wafers is removed in a KOH solution before cleaning them in a standard RCA sequence. The sample pro- cessing includes for most samples a phosphorus diffusion at 829 °C, resulting in n + -diffused regions with a sheet resistance of either around 47 Ω/square or 100 Ω/square on both wafer surfaces. The phosphosi- licate glass and the n + -regions are in most cases removed afterwards using an HF-dip and a KOH solution, respectively. The wafer surfaces are passivated with an Al 2 O 3 /SiN x -stack on both sides [14]. 10 nm of aluminum oxide (Al 2 O 3 ) are deposited using plasma-assisted atomic layer deposition (Oxford Instruments, FlexAl). 100 nm of silicon nitride (SiN x ) with a refraction index of 2.05 (Meyer Burger, SiNA) or 120 nm with a refraction index of 2.4 (Oxford Instruments, Oxford Plasmalab 80 Plus), are deposited by plasma-enhanced chemical vapor deposition. Furthermore, on some wafers the Al 2 O 3 layers are omitted. The wafers https://doi.org/10.1016/j.solmat.2019.110060 Received 5 April 2019; Received in revised form 10 July 2019; Accepted 13 July 2019 * Corresponding author. Institute for Solar Energy Research Hamelin (ISFH), Am Ohrberg 1, 31860 Emmerthal, Germany. E-mail address: m.winter@isfh.de (M. Winter). Solar Energy Materials and Solar Cells 201 (2019) 110060 0927-0248/ © 2019 Elsevier B.V. All rights reserved. T