Polycrystallin silicon as carrir slctiv contact for silicon solar clls SPREE Sminar Talk Udo Römr 21.07.2016
Outlin Tory / undrstanding poly-si contacts Local ovrcompnsation via ion implantation Procss optimisation poly-si contacts Combination of ts tcnologis 1
Motivation Rmoving front sid mtal sadowing ~2.5 ma/cm² gain in J sc PERC solar cll Poly-Si rar contact solar cll Voltag can b nancd by rducing rcombination: V SP-PERC cll as J 0 of ~300 fa/cm² Poly-Si / c-si-junction: 15 fa/cm² for p-typ poly-si 1 and OC kt Jgn ln 1 q J0 20 fa/cm² for n-typ poly-si 1 ~70 mv gain in V oc [1] J. Y. Gan and R. M. Swanson, IEEE Trans. Elctron Dvics, vol. ED-37, pp.245-250 (1990) 2
Enrgy [V] Poly-Si contact: working principl Band diagram of a n-typ poly-si contact (sktc) lctron transport many dfcts fw intrfac dfcts intrfac oxid: largr tunnl barrir for ols tan for lctrons Passivation: Transport: Low Tunnl D it transport at wafr surfac troug du t to oxid ig 1 or quality oxid Fild ols ffct in t passivation oxid 2 du to igly dopd poly-si layr Dpt [nm] [1] Stinkmpr, Fldmann, Bivour, and Hrml, IEEE Journal of Potovoltaics, vol. 5, no. 5, pp. 1348 (2015) [2] Pibst, Römr, Hofmann, Lim, Witlr, Krügnr, Hardr, and Brndl, IEEE Journal of Potovoltaics, vol. 4, no. 3, pp. 841 (2014) 3
Poly-Si contact: transport RCA-oxid aftr 10 min at 950 C RCA-oxid aftr 10 min at 1100 C HR-TEM invstigations sow braking up of t oxid aftr ig tmpratur procssing Wolstnolm, Jorgnsn, Asburn, and Bookr, J. Appl. Pys. 61, 225 (1987) 4
Procss flow poly-si tst structurs 1-stp-procss / 2-stp-procss Tin oxidation Dposition of dopd poly-si layrs Annaling / cracking of t oxid 5
Procss flow poly-si tst structurs 1-stp-procss / 2-stp-procss Tin oxidation Dposition of undopd poly-si layrs Annaling / cracking of t oxid Doping 5
Masurmnt of t rcombination caractristics Flas lamp 2.4 nm trmal oxid 30 min at 1050 C J 0 -tst structur Coil J 0 = 5 fa/cm² J 0 -dtrmination wit potoconductanc masurmnt and Kan & Swanson mtod 1 [1] Kan and Swanson, Proc.of t 18t IEEE PVSC, pp. 578 583 (1985) 6
Dtrmination of t contact rsistanc R poly R bulk R abs R poly R poly R poly R bulk R bulk R poly R poly Inductiv st rsistanc masurmnt 4PP st rsistanc masurmnt If oxid is prfctly insulating: R 4PP ~ R poly rl ~ 1 If oxid is prfctly conducting: R 4PP ~ R abs rl ~ 0 Römr, Pibst, Ords, Lim, Krügnr, Bugil, Witlr, and Brndl, Solar Enrgy Matrials and Solar Clls, vol. 131, pp. 85-91, Dc. 2014. 7
Simulation of 4PP-masurmnts SENTAURUS-DEVICE 3D-simulation Input paramtrs: Sampl gomtry Rsistivitis of wafr, poly-si layr and oxid Rsult: Masurd" st rsistanc Römr, Pibst, Ords, Lim, Krügnr, Bugil, Witlr, and Brndl, Solar Enrgy Matrials and Solar Clls, vol. 131, pp. 85-91, Dc. 2014. 8
Simulation of 4PP-masurmnts Calculation of rlativ contact rsistanc from simulatd 4PP rsistanc Plot vs. ral (spcifid) contact rsistanc Exampl: poly-si layr wit st rsistanc of 280 Ω/ : rl < 0.05 corrsponds to contact rsistanc of < 0.5 Ωcm² Römr, Pibst, Ords, Lim, Krügnr, Bugil, Witlr, and Brndl, Solar Enrgy Matrials and Solar Clls, vol. 131, pp. 85-91, Dc. 2014. 9
Invstigation of diffrnt oxids All oxids rac J 0 -valus btwn 5 and 20 fa/cm² Hig tmpraturs ndd for low contact rsistanc Boron-dopd poly-si contacts comparabl to Posporus-dopd Römr, Pibst, Ords, Lim, Krügnr, Bugil, Witlr, and Brndl, Solar Enrgy Matrials and Solar Clls, vol. 131, pp. 85-91, Dc. 2014. 10
Invstigation of diffrnt oxids Passivation stabl up to 60 min annaling at 1050 C Contact rsistanc dcrass wit incrasing annaling duration Good combination of low J 0 and rl possibl Römr, Pibst, Ords, Lim, Krügnr, Bugil, Witlr, and Brndl, Solar Enrgy Matrials and Solar Clls, vol. 131, pp. 85-91, Dc. 2014. 11
Influnc of t mtallization Mtallizd pics Liftim distribution masurd via Infrard Liftim Mapping (ILM) Solar cll dmonstrator ILM masurmnts bfor and aftr mtallization sow comparabl liftim lvl (apart from dg ffcts) Planar solar cll dmonstrators sow V oc of 714 mv 1 Sris rsistanc of 0.6 Ωcm² not limitd by poly-si contact 1 [1] Römr, Pibst, Ords, Lim, Krügnr, Bugil, Witlr, and Brndl, Solar Enrgy Matrials and Solar Clls, vol. 131, pp. 85-91, Dc. 2014. 12
Tory / undrstanding poly-si contacts Local ovrcompnsation via ion implantation Procss optimisation poly-si contacts 13
Local countrdoping wit in-situ pattrnd ion implantation Countrdoping: Ovrcompnsating on polarity of dopants wit dopants of t otr polarity Wit in-situ pattrnd countrdoping local doping possibl witout structurd dilctric layrs Countrdoping wit in-situ maskd ion implantation nabls lgant procss flow for back contactd solar clls Procss rsults in formation of latral pn-junction wit avily dopd p- and n-rgions - Risk for band to band tunnling - Risk for trap-assistd tunnling 14
Full ara countrdoping Procssing: - 1.5 x 10 15 cm -2 B implantation - 3 x 10 15 cm -2 P implantation - Annaling at 1050 C SIMS masurmnt: - Posporus profil covrs boron profil ovr wol dpt Countrdoping works fin! Römr, Pibst, Ords, Larionova, Hardr, Brndl, Gro, Stictnot, Wütric, t al., Proc. 39 t,ieee PVSC, pp. 1280 (2013) 15
Position z [µm] Local countrdoping Passivation layr Local posporus implantation p-typ silicon Position x [µm] Full ara boron implantation Aluminum contacts Simulations of t diod caractristics Masurmnts on tst structurs Simulations faturing latral pn-junction Variation of t liftim in t implantd ara Masurmnts on tst structurs and comparison wit simulations Römr, Pibst, Ords, Larionova, Hardr, Brndl, Gro, Stictnot, Wütric, t al., Proc. 39 t,ieee PVSC, pp. 1280 (2013) 16
Local countrdoping Simulations of t diod caractristics Masurmnts on tst structurs Simulations sow no dtrimntal influnc of igly dopd pn-junction: n = 1 as long as implant damag is wll annald Otrwis strong rcombination in spac carg rgion wit n = 2 Masurmnts on tst structurs sow n = 1 Evryting is fin! Römr, Pibst, Ords, Larionova, Hardr, Brndl, Gro, Stictnot, Wütric, t al., Proc. 39 t,ieee PVSC, pp. 1280 (2013) 17
Local countrdoping Furtr invstigations (incl. influnc of t latral doping profil & caractristics in rvrs dirction) publisd 1 Evryting is fin! Larg ara (156 mm x 156 mm psq.) ion implantd IBC solar clls faturing local countrdoping rac fficincis of 22.1 % 2 [1] Römr, Pibst, Ords, Larionova, Hardr, Brndl, Gro, Stictnot, t al., Proc. 39 t,ieee PVSC, pp. 1280 (2013) [2] Bosc Solar Enrgy, ISFH, prss rlas, Aug. 15t, 2013 18
Tory / undrstanding poly-si contacts Local ovrcompnsation via ion implantation Procss optimisation poly-si contacts Combination of ts tcnologis 19
Procss flow for ion implantd poly-si wit countrdoping Trmal oxidation LPCVD poly-si dposition Boron implantation Annaling/ oxid brak-up Boron implantd Tst structur Posporus implantd tst structur 20
Procss flow for ion implantd poly-si wit countrdoping Trmal oxidation LPCVD poly-si dposition Boron implantation Maskd posporus implantation Annaling/ oxid brak-up Boron implantd Tst structur Posporus implantd tst structur Tst structur full ara countrdoping 20
Procss flow for ion implantd poly-si wit countrdoping Trmal oxidation LPCVD poly-si dposition Boron implantation Maskd posporus implantation Annaling/ oxid brak-up Boron implantd Tst structur Posporus implantd tst structur Tst structur full ara countrdoping Tst structur local countrdoping 20
Ion implantation in poly-si Dcrasing J 0 wit incrasing dos Vry low valus of 1.1 fa/cm² (posporus) and 4.4 fa/cm² (boron) Incras at too ig doss, spcially for boron doping Römr, Pibst, Ords, Lim, Krügnr, Witlr, and Brndl, IEEE Journal of Potovoltaics, vol. 5, no. 2, pp. 507 (2015) 21
Ion implantation in poly-si Doping concntration constant insid poly-si layr Oxid acts as diffusion barrir, in particular for posporus For ig doss strong diffusion of boron into wafr Römr, Pibst, Ords, Lim, Krügnr, Witlr, and Brndl, IEEE Journal of Potovoltaics, vol. 5, no. 2, pp. 507 (2015) 22
Rcombination caractristics of boron-implantd tst structur Implantation dos: 1x10 15 cm -2 B Higst V oc,impl. valu rportd so far for p + dopd poly-si junctions Bst valu F-ISE 1 : 694 mv Hig pff impl. -valu of 84.6 % (idal valu for t givn V oc is 85%) Römr, Pibst, Ords, Lim, Krügnr, Witlr, and Brndl, IEEE Journal of Potovoltaics, vol. 5, no. 2, pp. 507 (2015) [1] Fldmann, Müllr, Ricl, and Hrml, Pys. Stat. Sol. RRL, pp. 1 (2014) 23
Rcombination caractristics of posporus-implantd tst structur Implantation dos: 5 x 10 15 cm -2 P Vry ig V oc,impl. of 742 mv Du to J 0,poly of only 1.1 fa/cm² and vry ig bulk liftim, rcombination caractristics at MPP dominatd by Augr rcombination n Augr 2/3 rsults in vry ig pff impl. Römr, Pibst, Ords, Lim, Krügnr, Witlr, and Brndl, IEEE Journal of Potovoltaics, vol. 5, no. 2, pp. 507 (2015) 24
Countrdoping in poly-si J 0 -valus comparabl to valus witout countrdoping Contact rsistanc of som sampls vry ig For otrs comparabl to sampls witout countrdoping Römr, Pibst, Ords, Lim, Krügnr, Witlr, and Brndl, IEEE Journal of Potovoltaics, vol. 5, no. 2, pp. 507 (2015) 25
Countrdoping in poly-si For som sampls diffusion of boron into t wafr No contact btwn n + poly-si and n-typ wafr Hig posporus doss prvnt in-diffusion of boron Römr, Pibst, Ords, Lim, Krügnr, Witlr, and Brndl, IEEE Journal of Potovoltaics, vol. 5, no. 2, pp. 507 (2015) 26
Rcombination caractristics of countrdopd tst structur Implantation doss: 1x10 15 cm -2 B 5x10 15 cm -2 P Vry ig V oc,impl. -valu Bst valu F-ISE: 682 mv 1 Dspit J 0,poly -valu of 0.9 fa/cm² pff impl. -valu of only 84.7% [1] C. Ricl, F. Fldmann, R. Müllr, A. Moldovan, M. Hrml, and S. W. Glunz, 29t EUPVSEC (2014) 27
Rcombination caractristics of maskd countrdopd tst structur Implantation doss: 1x10 15 cm -2 B 5x10 15 cm -2 P Curv only fitabl by adding a furtr rcombination pat wit n>2 Standard SRH-Tory: 1<n<2 in SCR Non-standard bavior.g. coupld dfcts 1 Römr, Pibst, Ords, Lim, Krügnr, Witlr, and Brndl, IEEE Journal of Potovoltaics, vol. 5, no. 2, pp. 507 (2015) [1] Stingrub, Britnstin, Ramspck, Glunz, Scnk, and Altrmatt, Journal of Applid Pysics, vol. 110, no. 1 (2011) 28
Rcombination caractristics of maskd countrdopd tst structur J L J cll J para R para R s Römr, Pibst, Ords, Lim, Krügnr, Witlr, and Brndl, IEEE Journal of Potovoltaics, vol. 5, no. 2, pp. 507 (2015) 29
Rduction of pn-junction rcombination Lowring of poly-si ticknss - Possibly problms wit mtallisation Adaption of implantation paramtrs - Lowr dos at pn-junction - Not vry lpful (s tsis) Rmoval of latral pn-junction - Oxidisation 1 - Wt cmical tcing η = 23.9 % 2 R s J cll J para J L R para V oc = 722 mv 2 FF = 78.7 % 2 [1] Pibst, Römr, Patnt application [2] Rinäckr, Mrkl, Römr, Kolnbrg, Krügnr, Brndl, and Pibst, 6 t SiliconPV Confrnc 2016 30
Summary Fast and non-dstructing mtod for t stimation of t contact rsistanc btwn diffrnt layrs Poly-Si contacts wit J 0 -valus of 0.66 fa/cm² and 4.4 fa/cm² for posporus and boron doping dvlopd Full poly-si contactd solar cll wit V oc of 714 mv and low contact rsistanc fabricatd 31
Summary Local ovrcompnsation via maskd ion implantation invstigatd Ovrcompnsatd poly-si contacts wit J 0 -valus of 0.9 fa/cm² fabricatd Anomalous rcombination baivour in locally ovrcompnsatd poly-si contacts invstigatd 32
Many tanks to You for your attntion Many collagus at ISFH and LUH for tir lp: Tobias Witlr, Robby Pibst, Susann Mau, Hik Kolnbrg, Miriam Brgr, Tobias Ords, Mical Häbrl, Jan Krügnr, Agns Mrkl, Bianca Lim, Yvgniya Larionova, Sara Spätlic, David Sylla, and vryon ls for t always nic atmospr T Laboratory for Nano- and Quantum Enginring Hanovr T BMWi for funding
Back-up slids
Influnc of procss squnc
Solar cll rsults full ara wafr impl. V oc = 716 mv impl. PFF = 84.5 % Bst procss usd for production of proof of principl solar clls Hig implid V oc masurd; implid PFF narly idal (85.0 %)
Solar cll rsults full ara wafr impl. V oc = 716 mv impl. PFF = 84.5 % lasr-cut into a 2.5 x 2.5 cm² pic impl. V oc = 714 mv impl. PFF = 72.7 % V oc = 705 mv PFF = 73.1 % V oc rducd furtr du to t dg ffcts (masurd troug 2 x 2 cm² mask) Masurmnt witout mask yilds V oc of 714 mv Larg ara solar clls would not suffr from tis ffct
Solar cll rsults Ara [cm²] V oc [mv] V oc [mv] (full ara illumination) PFF [%] FF [%] R s,ff [Ωcm²] J sc [ma/cm²] 4.25 705 714 73.1 71.2 0.6 28.8 14.5 η [%] Flat surfac of t solar cll and ratr tick poly-si layr (> 200 nm tick) Low J sc Edg rcombination Low PFF Excllnt passivation quality of t poly-si layr ig V oc Good transport troug t poly-si / c-si junction low R s