Silicon Thin Films. Hydrogenated amorphous silicon: hydrogen related structure and metastability Arno Smets (Delft University of Technology)

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1 Silicon Thin Films Report de couches Si cristallin Valérie Depauw (IMEC, Belgique) Cellules tandem a-si:h / µcsi Mathieu Despeisse (IMT-EPFL, Neuchatel) Epitaxie plasma de silicium à basse température et cellules hétérojonction Romain Cariou (LPICM) Hydrogenated amorphous silicon: hydrogen related structure and metastability Arno Smets (Delft University of Technology) 1

2 Silicon thin films Source: NREL, USA 2

3 Record stable efficiency : 13.4 % Record initial efficiency : 16.3 % B. Yan,, S. Guha et al., Appl. Phys. Lett. 99, (2011) Why thin film solar cells degrade? Because of SW in a-si:h top cells Need to replace Hydrogenated polymorphous silicon is a good alternative What is it? 3

4 Développement de filières en Couches minces de Si cristallin Transfert de substrats ultra-minces de silicium (20 à 50 µm) sur substrat bas coût Remplacer Si massif (200 µm) des couches de Si monocristallin (20 à 50 µm) reportées sur supports économiques Couche poreuse Si Epitaxie Si (1µm/min) Si p Si p + Soudure Al/Al Détachement US Si p Céramique ou verre p + Techno cellule HIT (T<250 C) Si p Céramique ou verre n + p + Réutilisation du substrat Faible porosité Forte porosité Substrat Silicium épitaxié Silicium poreux Substrat pv_video_layer_transfer_process.wmv Si poreux en bi-couche Epitaxie sur Si poreux * Collaboration INL - LPICM Couche de Si (20µm; diamètre 100 mm) reportée sur verre Cellule à hétérojonctions a-si/c-si * 4

5 PECVD: low temperature processes a-si:h, µc-si:h, Plasma texturing 1 Plasma cleaning 2 P/N junction 3 Heterojunctions Plasma epitaxy 1. M. Foldyna, M. Moreno, P. Roca i Cabarrocas, Applied Optics 49 (2010) M. Moreno, M. Labrune, and P. Roca i Cabarrocas. Solar Energy Mat. and Sol. Cells, 94 (2010) M.Labrune, M. Moreno and P. Roca i Cabarrocas. Thin Solid Films 518 (2009)

6 MULTI_SCALE ELECTRODES FOR 14 % INITIAL 12 % STABLE TANDEM CELLS 6

7 Thin epitaxial HJ solar cells Sample Jsc ma/cm 2 Voc V FF % Eff % A 18, , A 1h-200 c 19, ,5 Excellent Fill Factor Efficiency limited by Jsc Ligth trapping Crystalline silicon at the cost of amorphous silicon 7

8 2 Defect states in divacancies: H redistribution Earlier suggested: proton motion No gap-states D.E. Carlson et al., JAP 83, 1726 (1997). e - Gap-states h + 8

9 Crystalline Silicon & Si thin films Two parallel paths? For how long still? Low T Si thin films Polymorphous silicon µc-si:h,f, µc-siox Epitaxial growth SiNW radial junction Tandem and triple junctions High T c-si thin films P/N junctions IBC/HET CVD SPC, RTA, Up to 16.3% so far Up to 25% Increase efficiency Triple junction, light trapping Solve SWE Reduce costs Go thin Light trapping Merging of technologies (Heterojonctions) Towards high efficiency (> 25%) & flexible via low cost processes 9

10 Silicon Thin Films Report de couches Si cristallin Valérie Depauw (IMEC, Belgique) Cellules tandem a-si:h / µcsi Mathieu Despeisse (IMT-EPFL, Neuchatel) Epitaxie plasma de silicium à basse température et cellules hétérojonction Romain Cariou (LPICM) Hydrogenated amorphous silicon: hydrogen related structure and metastability Arno Smets (Delft University of Technology) 10

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12 Understanding the kinetics Annealed for 2 hrs Annealed for 2 hrs Efficiency (%) Interface Initial delamination degradation Al back reflector used 1 sun illumination Stable Stable Bulk How can we suppress the initial degradation? a-si:h PIN pm-si:h PIN Light Soaking Time (Hours) 12 October 9, 2012 PhD Defense Ka-Hyun KIM Amphi Becquerel Ecole Polytechnique 12

13 Stable pm-si:h NIP solar cells η stable from 4 % to 8.4 % 13 October 9, 2012 PhD Defense Ka-Hyun KIM Amphi Becquerel Ecole Polytechnique 13

14 Proof of concept: des cellules solaires à jonction radiale stables, avec un fort courant et excellente stbilité Current Density Jsc (ma/cm 2 ) Sample Voc Jsc F.F. Eff Degradation Status (V) (ma/cm2) (%) (%) (%) Initial LS-120h Radial Junction thin film solar cell with ONLY ~ 100 nm a-si:h as absorber Initial thin film RJ solar cell After light soaking for 120h -0,4-0,2 0,0 0,2 0,4 0,6 0,8 Voltage (V) Key Achievements: 1. Record-setting radial junction solar cell in the world 2. First ever demonstration of an improved stability in radial junction solar cell device 3. All-in-situ fabrication, compatible to established thin film production line Solar Energy Materials & Solar Cells, 94, 1855 (2010); Effective density control for Progress. in Photovoltaics: Research & Applications, /pip.1245 (2011) optimal performance Journées Nationales du PhotoVoltaïque, Nano Letter Chantilly, (2012) du & Nanotechnology 11 au 14 décembre (2012) 2012 (Invited) 14