纳米技术在太阳电池中的应用.pdf

纳米技术在硅薄膜太阳电池中的创新应用纳米技术在硅薄膜太阳电池中的创新应用 applicationof nanotechnology insiliconthin filmsolarcellsapplicationof nanotechnology insiliconthin filmsolarcells wenzhong shen (沈文忠)wenzhong shen (沈文忠) instituteofsolarenergyinstituteofsolarenergy shanghaijiaotonguniversityshanghaijiaotonguniversity e-mail:e-mail: tel such carriers are called “hotelectrons and hotholes” hot carrierscheme utilize the hot carriersbeforethey relax to the bandedge via phononemission 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m two fundamental ways forthe hot carrierapproachtwo fundamental ways forthe hot carrierapproach enhanced photovoltage:the carriers mustbe extracted from the photoconverterbefore they cool, i.e., rates of photogenerated carrierseparation, transport, and interfacial transferacross the contacts to the semiconductormustall be fastcompared to the rate of carriercooling enhanced photocurrent: the energetic hotcarriers produce a second (ormore) electronhole pair(carrier multiplication) through impact ionization, requiring the rate of impact ionization be greaterthan the rate of carriercooling and other relaxation processes forhotcarriers impactionizationprocess is the inverse of anaugerprocess: two electronhole pairs recombine to produce asingle highly-energetic electronhole pair 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m the qds are formed into anordered3d array with inter-qd spacing sufficiently small suchthatstrong electronic coupling occurs andminibandsare formed to allow long-range electron transport opportunities in low-dimensional semiconductorsopportunities in low-dimensional semiconductors quantumdotarrays inpincells the qd array is a3d analog to a1d superlattice and the miniband structures formed therein. the delocalizedquantized3d miniband states couldbe expected toslowthe carriercooling andpermitthe transport andcollectionof hotcarriers atthe respective pandn contacts to produce a higherphotopotential inapv cell physicae 1414, 115 (2002) 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m observation of minibands in nc-si:hobservation of minibands in nc-si:h the photocurrentof the nc-si:hheterostructure canbe decomposedinto two gaussian-shapedh- andl-peaks, whichare10100times largerthan the broad backgroundphotocurrentfromthe c-si substrate n h-peak(1.6 ev) photocurrentcanbe easily attributed to the electronic transitions fromthe tail bandof a-si boundaries innc-si:h n itis the misalignmentof the nanometer graindiscrete levels in energy due to the grain size distribution thatcauses the h-peakphotocurrentto quench with the decreasing temperature and become atemperature-independent steplike structure j. appl. phys. 102102, 123708 (2007) 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m observation of minibands in nc-si:hobservation of minibands in nc-si:h in the nc-si:h, the high density of nanometergrains embeddedin the very thin a-si:hboundaries that results in asuperpositionof aminibandwithasi-like bandgap in the tail bandof a-si:h n successful explanationof the l-peak(1.2ev) photocurrentby the classical theory due to the phonon-assisted transition indicates thatthe energy bandof the continuous states is also formed in the nc-si:hthinfilmlike thatinc-si n l-peakphotocurrentfromthe transitions of the si-like continuous energy band is very narrow in terms of the energy width(linewidth300mev), butis quite largerthan the phonon energy of nc-si:h thin film, which means aminiband 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m meg: nanotechnology for newconcept solarcellsmeg: nanotechnology for newconcept solarcells nabsorptionof asingle photon produces a single exciton, the photon excess energy is dissipated as heatviaphononemission nqe of photon-to-excitonconversion is zero below eg, and is 100%above it nshockley-queisser“ultimate” limit shows a maximum of 44%ataneg of 1.1ev nthe numberof excitons produced by a single photon is only limited by energy conservation, photons with energies eg, 2eg, and3eg produce one, two, and three excitons, respectively nthe corresponding qe is describedby a staircaselike spectral dependence, in whichqe increases by 100%when the photonenergy is increased by eg npowerconversion efficiency approaches 100%in the limit eg0 nature physics 1 1, 189 (2005) 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m evolution of the electronhole systemevolution of the electronhole system nabsorptionof aphoton(attime t1) with energy greaterthanthe cmthreshold results inthe generationof ahot bi-exciton(att2) on the timescale of tcm. nafterrelaxing to its ground state (att3) with the sub-picosecond time constant tr, this bi-exciton recombines on the sub-nanosecond timescale (ta) by the non-radiative augerprocess to produce asingle exciton (att4). nfinally, the excitonrecombines radiatively on amuch slowertimescale of tens to hundreds of nanoseconds. two-exponential fitindicates the presence of the short-livedbi-excitonic component andslow decay of single excitons in 3.2-nm-radius cdse nanocrystals (eg=2.0ev) 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m high efficiency carriermultiplication in pbse nanocrystalshigh efficiency carriermultiplication in pbse nanocrystals the firstobservationhas been demonstrated in pbse nanocrystals the limitof exciton multiplicity: qe increases linearly withaslope of 114%/eg until itreaches 700% (seven excitons persingle absorbedphoton) above the cmactivationthresholdof 3eg phys. rev. lett. 9292, 186601 (2004) nano lett. 6 6, 424 (2006) 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m multiple exciton generation efficiency in coupled pbse qd filmsmultiple exciton generation efficiency in coupled pbse qd films the qy results forcoupledqd films are similarto whathas beenpreviously reported forisolateddots suspendedin solvents the ability to effectively couple qds withoutreductionof meg is very encouraging forthe developmentof novel high-efficiency solarcells employing close-packedarrays of qds nano lett. 7 7, 1779 (2007) 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m 科学前沿:科学前沿:colloidal quantum-dot photodetectorscolloidal quantum-dot photodetectors exploiting multiexcitongenerationexploiting multiexcitongeneration photoconductive gainresults when the flowing carrier(such as holes) can be recirculated multiple times during the lifetime of the trapped carrier(electrons): many charge carriers may be collectedforevery exciton generated. science324324,1542(june19,2009) pbspbs 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m 本资料来源于网络，版权归原著作所有，禁止使用于一切商业行为，仅供交流学习用！请在下载后24小时内删除！ 21spv光伏社区 b b s .21s p v .co m multiple excitongeneration in colloidal siliconnanocrystals towards the realization of si meg solarcellstowards the realization of si meg solarcells n particularimportance because si dominates the pv solar cell industry n the thresholdphotonenergy formeg is 2.4eg and that the quantumyieldof excitons producedperabsorbed photon reaches 2.6 at3.4eg n highly efficientmeg innanocrystalline si atlower photon energies in the visible regionhas the potential to increase powerconversionefficiency in si-basedpv cell