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用戶:Barbie0117/組織/鈣鈦礦太陽能電池

< User:Barbie0117

1. XRD Transition temp: A-1: annealing temp: know at which temp pero will produce tetragonal phase concentration: -MEASURE >in angle vs XRD intensity graph >peak shift >=right/left shift to differt angle> know ratio of Cl incorporated >bsc diffrt concen has diffrt peak


lattice parameters and unit cell volumes 

peak splitting >formation of phases with larger and smaller lattice constants>Know whether and when phase-separation will occur

-measure> in diffraction angle vs Log intensity > before illumination> one peak >after illumination > splitting to two & peak height drop>represent composition change

Determine if perovskites phase is constructed > Measure> angle-counts graph >cannot find peak for y=0.5-0.7 >this range cannot form perov structure -measure2 >lattice parameter -Eg graph >cannot find point for y=0.5-0.7 >this range cannot form perov structure

Which orientation the system prefer> -measure > intensity-2 angle graph >when range x=0~0.05 >peak appear in same angle > one angle represent one orientation >

Which facets/orientation intensity rise> -measure > intensity-2 angle graph >as range x=0.1~0.2 >peak at certain angle rises height > represent this facet intensiry rise At which concen hybrid perov structure will separate -measure > intensity-2 angle graph > range x bigger than 0.2 >new peaks observed >means new structure formed >so 0.2 =threshold limit for the full-miscibility


2. UV−vi

a. optical band gap: optical band gap> the sharp drop in reflectance> the point = band gap> in photon energy- Tauc plots of UV−vis reflectance spectra q:-measure B. absorption edge +wavelength measure> absorbance - wavelength graph>large slope line> extend to x axis> get absorption edge of wavelength

C. Determine if perovskites phase is produced> -measure >wavelength-absorbance >cannot find line for y=0.5-0.7 >this range cannot form perov structure D. diffrt concen/composition -measure >absoprtion-wavelenrth graph >diffrt line/peak >means difrt X concen/composition


3.PL

A. peak splitting>Know whether and when phase-separation will occur -measure > in PL-Energy graph > after illumination > peak shift lower energy (to left) >and peak higher > more cycle >peak height drop


B. Determine if perovskites phase is produced> -measure >wavelength-PL >cannot find line for y=0.5-0.7 >this range cannot form perov structure

C. PL lifetimes q:-measure

D. fwhm of pl >correlated with >Urbach energies Q: -measure > E. traps lifetime Q: -measure>

Q: what does PL’s lifetime mean? 4.SEM


Causal: 1. Band gap /photoluminescence/absorption/ Urbach energies -optical band gap drop >=photon energy drop > as FA ratio rise -MA ratio=0>optical band gap drop not linear> bcs tetragonal structure stabilized at room temperature.> -xFA rise from 0.2 ≤ x ≤ 1 >UV-vis linear drop in optical band gap >corresponding to the range of compositions adopting the cubic unit cell at room temp (FAxMA1-xPbI3 ) -defect states localized at the grain boundaries. > sub-band gap absorption is due to 226 -dependence of x &Urbach energies >related to grain-size domains >AND fwhm of the PL peaks >correlated with the Urbach energies >AND larger PL fwhm & Urbach energy >correlate with shorter lifetimes observed in transient PL >with iodine concen of 20−40% > MAPb(I/Br) /FAPb(I/Br) -after illumination> PL with continuous wave (CW) or 10 ns pulsed laser >with high repetition rates, >initial PL peak position shifted to a longer wavelength >BUT using lower repetition rates (<500 Hz) >no matter what the intensity of excitation light >PL peak not shift >REASON >initial photon absorption >generate trap states within bg=band gap >these traps not cause PL emission >traps lifetime of 1 μs (Phase A) >If subsequent incident photons are absorbed by these traps within the lifetime >transforms to a long-lived "metastable」 state (Phase B) >which behaves as new energy band >lead to PL emission > These polar states/olaronic states>locally drive ion migration .

each of the domains (iodideand bromide-rich) having characteristic conduction band minimum (CBM) and valence band maximum (VBM) values will lead to iodide-rich domains to serve as charge recombination sites and thus contribute to the observed PL emission (Figure 16c). MAPb(I/Br)


2. Transition/phase se -MA ratio closer to 0.4> Transition temp min> stability rise> not transit from cubic to tetragonal structure easily > but>bigger/smaller than 0.4> Transition temp rise -phase segregation change in 250k-350k -Phase segregation => black α-phase turn to other phase(δ)> - Rb present >enthalpy of transition smaller>smaller area under the transition peak in DSC curve > transition to α-phase more favorable> also δ→α phase transformation kinetics faster -in postannealing >phase transition occur >from tetragonal to a cubic > then stabilized after cooling at room temp (MAPbIClx) -annealing at 140 °C >produce tetragonal (FAPbI3−xClx ) -add NH4Cl, MACl additive>suppress the formation of yellow δ-phase FAPbI3. >achieving high-purity black α phase (FAPb(I/Cl) ) >after illumination > diffraction pattern splits into two peaks >formation of phases with larger and smaller lattice constants >undergo photoexcited phase-separation into two phases>iodine-rich /bromide-rich domain in the same film >BUT> relax in dark>XRD pattern returned to its original>back to single phase state (MAPb(BrxI)

  • after storage under dark and inert environ >without light illumination >PL peak position shift films to lower e.v. >MAPbBr1.2I1.8


Q: why annealing turn to tetragonal, not cubic

3. Dopant ratio/incorporation -PbCl2:PbI2 mole fraction rise> Cl ratio rise>partial substitution of Cl− into the perovskite structure>>diffraction peaks shift > absorption edge shift to short wavelength -two-step dipping method> dope more Cl-content > than one-step method. -incorporate Cl in MAPbI3 > by 1.controlling the annealing time 2. Diffe precursor sol -Cl x = 0 >exhibit preferred orientation along ⟨110⟩ directions (MAPbI3 and MAPbI3-xClx ) -x = 0.1 and 0.2 concentration >(112) and (200) facets increased in intensity ((CsPbBr3)x ) -high intensity of (110) diffraction planes observed >so Cl-inclusion only along the [001] direction > (MAPbIClx) -Cl dope>so c lattice parameter drop (FAPb(I/Cl) ) - range of 0.3 < x(Br) < 0.5 >no line/data in UV-vis, PL, and XRD graph >unable to form crystalline phases (FAPb(I1-xBrx)3) >means amorphous structure >crystalline order is too short in the length scale detectable by XRD

  • x bigger than 0.3>new peaks assigned to CsPb2Br5 observed in XRD>means x = 0.2 is threshold limit for the full-miscibility混和性 ((MAPbI3)1-x(CsPbBr3)x.)
  • xBr rise >XRD peak shift right to higher angle >& UV-vis absorption edge shift right to highrt wvlth >FAPbIBrx

4. pce/performance -facet-orientation in single grains of perovskites. >determine photovoltaic efficiency -mixed FAxMA1−xPbI3 nanorods >presented longer photoluminescence (PL) lifetimes >than the pure FAPbI3 and MAPbI3 -xFA=0.4 >longer PL lifetimes >correlated with lower density of defects > resulting in high performance. >FA0.4MA0.6PbI3

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