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ARCPHOTOVOLTAICSCENTRE OFEXCELLENCE2010/11ANNUAL REPORTSEM cross-section of CZTS-type cells (Todorov et al., Adv. Mater. 22,E156, 2010).Figure 4.4.3.2a more attractive process because large area/highrate sputtering is a better developed techniquethan evaporation. In addition, sputtering hascommercially available equipment that gives gooduniformity over large areas. UNSW has considerableexperience in PVD techniques, such as theachievement of the first silicon quantum dot solarcell on quartz [4.4.3.3], a recent patent relating tocrystal Ge on Si wafer by a sputtering technique andthe polycrystalline silicon thin film solar cell on glassby an evaporation technique [4.4.3.4].Almost all of the methods that have beenattempted for CZTS fabrication involve two steps;deposition of a metal/metal-sulfide precursorand a subsequent anneal at high temperaturein a hydrogen sulphide or elemental sulphurenvironment to incorporate more sulfur into thefilm and evolve the correct phase [4.4.3.5-4.4.3.7].It is reported that the H 2S/sulphur anneal is adestructive process that can potentially introducedefects into the film due to the out-diffusion ofmetals. In addition, for large scale production ofsolar cells, a direct one-step, large area depositionprocess is preferred.Fortunately, reactive sputtering is a well suitedtechnique because of the above-addressed featureof precise control on the stoichiometry of depositedfilms over a large area with high uniformity at arelatively low cost. The experience documented inour patent of “A Method of Forming A GermaniumLayer On A Silicon Substrate And A PhotovoltaicDevice Including A Germanium Layer”, where theintroduction of H 2gas into the in-situ depositedgermanium thin film by magnetron sputteringresults in the significant improvement of theperformance of germanium thin film, appearshighly relevant.As such, the idea of one-step reactive sputteringby in-situ introducing H 2S gas into the depositedCZT (Cu 2ZnSn) film is a logical step to attempt abetter CZTS film quality. However, there have beenfew attempts to date at such a simplified one-stepprocess by introducing the sulphide into the CZTSfilm during in-situ deposition. In addition, thisprocess is not well understood and significantlymore effort is required in order to understandgrowth mechanisms involved in the reactivesputtering process. Comparison of reactivelysputtered films with 2-step sulphidisation processeswill provide the early emphasis of the Centre’s work.4.4.3.3 References4.4.3.1 T.K. Todorov, K.B. Reuter, D.B. Mitzi, AdvancedMaterials 2010, 22, E156.4.4.3.2 W. Liu, D.B. Mitzi, M. Yuan, A.J. Kellock, S.J. Chey,and O. Gunawan, Chem.Mater., 2010, 22(3), 1010-1014.4.4.3.3 I. Perez-Wurfl, X.J. Hao, A .Gentle, D-H. Kim, G.Conibeer, M.A. Green, Applied Physics Letters 95(2009), 153506.4.4.3.4 Z. Ouyang, S. Pillai, F. Beck, O. Kunz, S. Varlamov, etal., Applied Physics Letters, 2010, 96 (26), 261109.4.4.3.5 J.J. Scragg et al., Thin Solid Films, 517 (2009), pp.2481-2484.4.3.3.6 R. Schuee et al., Thin Solid Films, 517 (2009) pp.2465-2468.4.4.3.7 Hironori Katagiri et al., Thin Solid Films, 480-481(2005), pp. 426-432.60
4.5 Third Generation Strand –Advanced ConceptsUniversity Staff:• A/Prof. Gavin Conibeer (group leader)• Dr Richard Corkish• Prof. Martin GreenSenior Research Fellows:• Dr. Dirk König• Bo Zhang• Andy Hsieh• Dawei DiARCPHOTOVOLTAICSCENTRE OFEXCELLENCE2010/11• Zhenyu “Wayne” WanANNUAL REPORT• Craig Johnson• Sammy Lee• Haixiang ZhangResearch Fellows:• Dr Shujuan Huang• Dr. Ivan Perez-WurflLecturers:• Dr Santosh ShresthaPostdoctoral Fellows:• Dr Supriya Pillai (part time)• Dr Xiaojing “Jeana“ Hao• Dr Sangwook Park (to Apr 2010)Professional officers:• Dr Tom Puzzer (part time)• Dr Patrick Campbell (shared with ThinFilm)• Mark Griffin (shared with Thin Film)Research Associates:• Dr Didier Debuf (adjunct fellow)• Yidan Huang• Lei “Adrian” Shi (from Sept 2009)Higher Degree Students:• Lara Treiber• Pasquale Aliberti• Yong-Heng So• Robert Patterson• Binesh Puthen Veettil• Chao-Yang “Jeff” TsaoCasual Staff:James Rudd (part time)Visiting Researchers:• Dr. Yukiko Kamikawa (AIST, Tsukuba,Japan, June 2009 – Dec 2012)• Prof. Bingqing Zhou (Inner MongoliaNormal University, China, Sept 2009 –Aug 2010)• Dr. Mallar Ray (Bengal Eng. and Sci.University, May 2010)Undergraduate Students:4 th Year Thesis Projects:• Yu Feng• Tao Zhan• Chen Pan• Xi Li• Yao Yao• Linzhi Ma• Lin DongMasters Project:Chandraprasad RamachandranVisiting Practicum students:• Stephan Michard (RWTH Aachen,Germany, Aug 2009 – Feb 2010)• Dolf Timmerman (AmsterdamUniversity, Oct – Dec 2010)AbstractThere has been approximately equal work onthe two major projects in Third Generation in2010. These are the Group IV nanostructuretandem cells project - the “all-Si” tandem cell- and the Hot Carrier solar cell project, withits continuing funding from GCEP (GlobalClimate and Energy Project). There has alsobeen further work on Up-conversion and onPlasmonics.The Si nanostructure work has seen increasedunderstanding of the mechanisms fortransport and quantum confinement. Moresophisticated modelling of both has beentied more directly to improved interpretationof experimental results. This has led toestablishment of a predictive ‘equivalent circuitmodeller’ which will allow optimisation of SiQD device parameters to maximise transportand performance in the photovoltaic devices.Improved models for the understandingof doping effects in these materials havealso been established. Work on alternatematrices for Si quantum dots, in both siliconnitride and carbide, has seen development ofcomposite structures which have improvedtransport in the growth direction, whilstmaintaining quantum confinement in theplane, but which also increase the uniformityof QD sizes. Work on Ge nanostructures hasalso improved with high electrical p-typeconductivity established for Ge quantumdots and excellent pseudo single crystallinegrowth quality for Ge quantum wells in anitride matrix. Heterojunction photovoltaicdevices combining the advantages of two ofthese different material types are now beinginvestigated.Hot Carrier cells have seen very significantimprovement in demonstrated resonancein energy selective contacts using Sinanostructure layers, as well as a developmentof 2 and 3D modelling of transport in thesestructures. Modelling of Hot Carrier efficienciescontinues to get more sophisticated withapplication to real material systems such asIII-nitrides and inclusion of Auger processeswhich become significant at high carrierconcentrations. Work on absorbers hasallowed modelling of the phononic propertiesof a range of bulk materials, in conjunctionwith time resolved photoluminescencemeasurement of carrier cooling in some ofthese materials. Also modelling of coherentnanoparticle nanostructures, which emulatethe phononic properties required, hasdeveloped into direct application to structuresgrown directly. These structures include the61
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