Investigating manufacturing options for industrial PERL-type Si solar cells Antonio Cacciato n , Filip Duerinckx, Kasper Baert, Matthieu Moors, Tom Caremans, Guido Leys, Koen De Keersmaecker, Jozef Szlufcik Photovoltech N.V., Industrial Area WestGrijpen, Grijpenlaan 18, B-3300 Tienen, Belgium article info Article history: Received 22 October 2012 Received in revised form 2 February 2013 Accepted 8 February 2013 Available online 15 March 2013 Keywords: Solar cells High-efficiency PERL BSF ELA abstract In this paper the tradeoff between process control and cost-effectiveness for PERL-type process flows is investigated. Three aspects are considered: (1) whether a surface pre-treatment (for example special cleans and/or oxidation) prior to the deposition of the Al 2 O 3 -based rear-side passivation stack has to be added to the flow; (2) the quantification of the impact on cell parameters of skipping the rear-side polishing and/or the Al 2 O 3 deposition; and (3) the possibility of replacing Al paste with PVD Al for rear side metallization. It is found that: (1) SPM-like cleans or thermal oxidation prior to Al 2 O 3 deposition are useful steps to guarantee a stable Al 2 O 3 -based passivation process. (2) The efficiency drops by more than 1% by skipping the polishing, but only E0.15% by removing the Al 2 O 3 from the passivation stack. Therefore, while rear-side polishing appears to be a necessary step for PERC/PERL technologies, the insertion of Al 2 O 3 in the passivation stack could be traded off for a reduced production cost, depending on the (company-specific) details of cost-calculations. (3) Replacing Al paste with PVD Al for rear side metallization results in a deteriorated reflectance. The effect is larger for thinner passivation stacks. Although less advantageous in term of material costs with respect to PVD Al, screen-printed Al would therefore be the preferred choice for PERL cells featuring thin passivation stacks. & 2013 Elsevier B.V. All rights reserved. 1. Introduction One of the main reasons of the delay in the widespread industrialization of the passivated emitter, rear locally diffused solar cells (PERL) architecture [1,2], is the immediate cost issue arising from an increased number of production steps and from novel type of equipments compared to the standard full Al-BSF- type architecture. In general, an ideal industrial PERL flow would contain no extra cleans and the minimum number of added process steps for rear-side passivation, metallization and contact- ing, while guaranteeing at the same time higher efficiency and controllability with respect to the mature full Al-BSF technology. Aiming at achieving this goal, recent years have seen an increasing focus on the development of cost-effective rear surface passivation [3–7], laser contacting [8–11] and metallization [12–15] schemes. In previous papers we have optimized the rear contacting process, introducing a new rear contacting technique (named Extended Laser Ablation or ELA), which results in a high quality local back surface field (BSF) around the rear contacts [16], and we have integrated Al 2 O 3 layers into a PERL-type flow [17]. These investigations together with the further optimization of the emitter diffusion/oxidation processes and of the rear-side printing have allowed us to define an optimized PERL-type flow capable of top efficiencies of 19.7%, while keeping the process complexity at a minimum [18], i.e. while using a standard design on the front side (homogeneous emitter—75 O/sq–SiN x ARC–screen-printed contacts), thin dielectric layers on the rear (  100 nm AlO x /SiN x stack), and no final Forming Gas Anneal treatment (FGA) (often used for cells with passivated rear side to heal laser damage and recover high V oc values [19]). In this paper we address in more detail the tradeoff between the process stability/efficiency and cost-effectiveness. In particu- lar (1) we investigate the opportunity of inserting PERL-specific clean or a thermal oxide prior to the Al 2 O 3 deposition; (2) we quantify the effect of skipping rear-side polishing on cell para- meters; and (3) we discuss the limits of replacing for the rear side metallization of the screen-printed Al paste with the potentially more economic physical vapor deposition (PVD) of Al. 1 2. Experimental PERL cells were fabricated on 156 mm  156 mm, 200 mm- thick, p-type Cz mono-crystalline silicon wafers with resistivity Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.solmat.2013.02.012 n Corresponding author. Present address: Abdijstraat 16a, 3001 Leuven, Belgium. Tel.: þ32 473 784423. E-mail address: acacciato@katamail.com (A. Cacciato). 1 Although capital expenditures for PVD Al deposition are still very high (and no real industrial system is available yet), Al consumption (and therefore material costs) is reduced compared to screen printing of Al paste. Solar Energy Materials & Solar Cells 113 (2013) 153–159