l-uminum Screen-Printed IBC Cells: Design Concept Paul Basore, Emmanuel Van Kerschaver, Kirsten Cabanas-Holmen, Jean Hummel, Yafu Lin, C Paola Murcia, Kate Fisher, Simeon Baker-Finch, Oun-Ho Park, Frederic Dross,Evelyn Schmich, Wibke Wittmann, Venus Noorai, Dilip Patel Hanwha Solar America First presented at the 39 th IEEE PVSC Tampa, FL, 18 June 2013
Hanwha-Q.Cells Solar Technology Teams R&D and pilot-scale production Lemoine Research Centre (Thalheim) Germany China Solar R&D Center (Daejeon) Korea US Cells and modules (Cyberjaya) Malaysia Hanwha Solar America Advanced R&D Laboratory (Santa Clara/Silicon Valley) Ingots, wafers, cells, modules Solar Technology Center (Qidong) Hanwha-Q.Cells is one of the world s three largest PV manufacturers (capacity 2.3 GW/yr) 2
Motivation Front contacts block light Silver is expensive l Back Contact (IBC) l uminum (Screen Print) 3
Objections to l-back-contacts n-type wafers are expensive Use p-type Cz wafers Design for 100 ms lifetime Can only allow one high-temp Diffuse phosphorus -alloy for p-type contact Patterned diffusion is difficult Etch trenches after diffusion Screen print trench pattern 4
Objections to uminum Gridlines will fire through emitter Passivation layer barrier Non-alloying paste won t form BSF loy-optimized paste Higher firing temperature is not sufficiently conductive Reduce gridline length Cleave wafers into strips 5
SPLICE o Screen Printed Locally Interdigitated Contact Elements* Low-cost adhesive tape 156 mm *Trademark and patents pending Cell separation cleaves along laser grooves Printed cell interconnects 6
SPLICE Cell and Module Structure etched-back n + diffusion p + alloy p-type Cz wafer n + diffusion SiN x Bipolar passivation Tab o 6 wafers across, 10 cell strips per wafer = 60 cells per string o 10 strings down length of module o Single copper tab along each edge, thin-film style o Normal I sc, V oc 7
SPLICE Cell Fabrication Sequence 156-mm wafer p-type Texture etch, HF-HCl clean, rinse and dry
POCl 3 Diffusion, Print Etch Paste POCl 3 diffusion, 80 ohms/sq Screen print oxide-etch paste on 1.2-mm centers Belt heating etches PSG 300 mm trench
Etch Trenches, Remove PSG, Etch-back kaline etch removes etch paste and ~2 mm silicon PSG protects surface elsewhere HF-HCl etch removes remaining PSG Weak single-side etch front surface to 200 W/sq Rinse and dry
PECVD Passivation of Both Surfaces Bipolar rear passivation O x SiN x or equivalent (firing stable) SiN x :H front-surface passivation and ARC
Screen Print Metallization Print and dry p-type gridlines Belt fire so forms p + alloy p + p + Print and dry n-type gridlines Belt fire so contacts the n + but does not form alloy
PC2D Cell Performance Modeling r=92% r=90% T=98% 200 W/sq p-type 1E16 cm -3 t=100 ms r=70% J o1 =500 fa/cm 2 J o1 =10 fa/cm 2 J o1 =70 fa/cm 2 80 W/sq 150 mm 0.3 mm 0.1 mm 0.6 mm 0.6 mm R metal = 0.4 Wcm 2 Electron quasi-fermi potential at max-power point Max (dark green) Min (dark blue) = 39 mv {Hole quasi-fermi potential Max-Min = 8 mv} 3.6 ma/cm 2 lateral current flow in FSF helps collection over trench areas 13
Modeling Results 20.5% 14
Summary o SPLICE = Screen Printed Locally Interdigitated Contact Elements p-type IBC structure to improve efficiency uminum gridlines for both contact polarities to reduce cost Cleaved cell strips interconnected with printed metal at module scale o Performance Modeling Cell efficiency for 100 ms lifetime exceeds 20% Floating front junction reduces electrical shading o Key challenges Identification of best metal pastes for n-type and p-type contacts Optimization of rear dielectric passivation stack Development of metal extrusion printing process for cell interconnection o If you have experience related to this concept, please share what you know! 15