This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE JOURNAL OF PHOTOVOLTAICS 1 On the Nature of Emitter Diffusion and Screen-Printing Contact Formation on Nanostructured Silicon Surfaces Bishal Kaﬂe, Timo Freund, Sabrina Werner, Jonas Sch¨ on, Andreas Lorenz, Andreas Wolf, Laurent Clochard, Edward Duffy, Pierre Saint-Cast, Marc Hofmann, and Jochen Rentsch Abstract—In this paper, we study the impact of change in emitter diffusion proﬁles on the electrical characteristics of nanotextured surfaces formed by an inline plasma-less dry-chemical etching pro- cess. Our experimental results and process simulations suggest that a deeper highly doped region and a signiﬁcantly higher inactive P concentration in the emitter plays a determining role in deﬁning recombination, as well as the resistive losses in nanotextured sur- faces. Low emitter saturation current densities on phosphorous- diffused surfaces are achievable after passivation with either SiN x (j 0e ,min ≈ 81 fA/ cm 2 ) or AlO x /SiN x (j 0e ,min ≈ 31 fA/ cm 2 ) if the emitter recombination channels are suppressed. Based upon macroscopic measurement of contact resistivity and microscopic analysis of the contact areas, we propose that the formation of numerous metal–semiconductor direct contact points on the peak and the plateaus of the nanostructures are mainly responsible for a low speciﬁc contact resistivity (ρ c ,min ≈ 1.2 mΩ · cm 2 ) achievable in these surfaces. Index Terms—Atmospheric pressure, contact formation, dry etching, emitter recombination, nanotexture. I. INTRODUCTION F ORMATION of submicrometer structures in crystalline silicon (c-Si) and multicrystalline silicon (mc-Si) surfaces signiﬁcantly enhances incident light absorption properties [1]. The formation of nanotexture, however, leaves a greatly en- larged Si surface that poses major challenges in surface passiva- tion and emitter formation process steps. Meanwhile, high solar cell efﬁciencies on mc-Si surfaces are achieved by optimiza- tion of these cell process steps on nanotextured surfaces that are formed by applying different texturing techniques [2]–[5]. We developed an atmospheric pressure dry-chemical texturing approach of forming nanotexture by utilizing spontaneous re- action of c-Si with F 2 gas [6], [7]. In our previous work, we Manuscript received September 27, 2016; revised October 25, 2016; accepted November 3, 2016. This work was supported by the German Federal Min- istry for Economic Affairs and Energy within the project APPI under Contract 0325895A. B. Kaﬂe, T. Freund, S. Werner, J. Sch¨ on, A. Lorenz, A. Wolf, P. Saint-Cast, M. Hofmann, and J. Rentsch are with the Fraunhofer Institute for Solar Energy Systems ISE, Freiburg 79110, Germany (e-mail: bishal.kaﬂe@ise.fraunhofer. de; timo.freund@ise.fraunhofer.de; sabrina.werner@ise.fraunhofer.de; jonas. schoen@ise.fraunhofer.de; andreas.lorenz@ise.fraunhofer.de; andreas.wolf@ ise.fraunhofer.de; pierre.saint-cast@ise.fraunhofer.de; marc.hofmann@ise. fraunhofer.de; jochen.rentsch@ise.fraunhofer.de). L. Clochard and E. Duffy are with Nines Photovoltaics, Dublin 24, Ireland (e-mail: l.clochard@nines-pv.com; e.duffy@nines-pv.com). Color versions of one or more of the ﬁgures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identiﬁer 10.1109/JPHOTOV.2016.2626921 showed that simultaneous tailoring of the nanostructure geom- etry and introduction of an in-situ oxidation during the POCl 3 diffusion process is able to minimize the surface and emitter recombination and improve the internal quantum efﬁciency of the mc-Si Al-BSF solar cell [8], [9]. In high-efﬁciency solar cell architectures like passivated emitter rear cells, however, the limit imposed on the maximum value of open-circuit volt- age (V OC, max ) due to the emitter recombination becomes much more important, as surface recombination velocity (SRV) of the rear side (S pass ) is no longer limiting the lifetime of generated charge carriers. Therefore, further tailoring of n-type emitter diffusion proﬁles is needed to allow high V OC values that are promised by high-efﬁciency solar cell architectures. However, modifying the emitter proﬁle directly inﬂuences the resistivity of the metal–semiconductor contacts as well as the recombina- tion losses in the space-charge region. In order to achieve high- efﬁciency emitters with low speciﬁc contact resistivity (ρ c ), a tradeoff between low recombination losses and low resistive losses needs to be considered. In addition, it is crucial to un- derstand the nature of screen-printed front-side Ag contacts on the nanotextured surfaces for the further optimization of the screen-printing process on rough surfaces. In this paper, we ﬁrst of all investigate the correlation of emitter diffusion proﬁles to the recombination losses in phosphorous-diffused nanotextured surfaces by estimating dark emitter saturation current densities (j 0e ) for different emitter proﬁles. Additionally, process simulations are performed to gain more insights about the nature of emitter formation in nanotex- tured surfaces. To correlate the contact formation process in nanotexture with corresponding emitter diffusion processes, we ﬁrst of all macroscopically investigate the contactability of dif- ferent emitter proﬁles by extracting speciﬁc contact resistivity (ρ c ) using the transmission line model (TLM) [10]. In addi- tion, methods like scanning electron-beam microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) are used to discuss microscopic phenomena of the contact formation and current transport mechanism in nanotextured surfaces. II. NANOTEXTURING PROCESS We use, as precursors, 15.6 × 15.6 cm 2 mono c-Si (p- and n-type) and mc-Si (p-type) wafers. To prepare nanotextured sur- faces, the precursors are ﬁrst saw-damage etched and then tex- tured by ﬂowing F 2 gas over the heated wafer (T wafer ≈ 170 ◦ C), which is moved through the reaction chamber with a set velocity 2156-3381 © 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.