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학습트랜스크립트
00:00안녕하세요. 저는 예찬신입니다.
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00:19이 수업을 진행할 수 있습니다.
00:22perubsigide solar cell.
00:25As mentioned in my previous presentation,
00:28there are various factors that contribute
00:31to the degradation of perubsigide solar cell stability.
00:35This can be broadly categorized into extrinsic factors
00:40and intrinsic factors.
00:42Extrinsic factors include oxide and moisture,
00:45heat, light, and ultraviolet exposure.
00:50On the other end, the extrinsic factors consist of ion migration,
00:55phase segregation defects, and lattice mismatch.
01:01These factors don't act independently.
01:04They're often interacting in complex ways, collectively
01:09accelerating the degradation of perubsigide solar cells.
01:16This slide illustrates the degradation mechanism caused by oxygen and moisture,
01:22which are two major extrinsic factors affecting perubsigide solar cells.
01:28Due to the presence of polar organications such as MA plus and AP plus,
01:36perubsigide materials are highly sensitive to moisture and oxygen.
01:41In stage A, moisture penetrates the perubsigide crystal and
01:47formed hydrate intermediates, destabilizing the structure.
01:54In stage B, an acidic environment develops within the hydrate phase,
02:01leading to the formation of hydroiodic acid and causing halide loss.
02:10In stage C, MA plus undergoes deprotonation, releasing CH3 and H2 gas, which irreversibly result in the collapse of
02:24the A-Cite Cation framework.
02:28Eventually, only PBI-2 remains, and water continuously re-engage in the reaction like catalyst,
02:38promoting liquid degradation.
02:41As such, as a result, the perubsigide film turns yellows, indicating chemical degradation and significant drop in device performance.
02:58This slide explains the thermal degradation mechanism of perubsigide solar cells.
03:04When the device is exposed to lights or environmental conditions, heat is generated lead to the temperature lights as shown in A.
03:16This increase in temperature causes a phase transition by increasing the symmetry of the crystal structure.
03:27During this process, the lattice expands and becomes more symmetric, but at the same time the lattice rigidity weakens,
03:41leading to structural instability.
03:46In particular, the free rotation of MA plus cations destabilizes the PBI-PB bond angles, which induced lattice strains, defects, and halide vacancies.
04:03And B, the PL spectra at different temperatures show a sharp decrease in PL intensity with increasing temperature.
04:20This indicates that non-radiative recombination pathways are activated, leading to loss of photo-generated charge carriers through defect states.
04:35She showed a shift in the PL peak position with a temperature change.
04:43As the temperature increase, the PL peak exhibit blue shift, which corresponds to band gap widening, changes in bond length, and progressive lattice dispersion inclusion.
05:01In conclusion, thermal stress weakens the lattice stability of the perovskite promotes defect formation and ion migration,
05:12and ultimately lead to structural collapse and device performance degradation over time.
05:22This slide explains the UV-induced degradation mechanism in perovskite solar cell.
05:30We will focus on how ultraviolet light affects TiO2, which is commonly used as the electron transport layer, as shown in A.
05:40When UV light is irradiated to TiO2, the energy exceeds the band gap, resulting in the generation of electron hole pairs.
05:52The photo-generated host oxidizes TiO2 to TiO2 plus, creating oxygen-bequensis defects, which in turn trap electrons and promote charge transfer toward the perovskite interface.
06:12These electrons reduce Pb2 plus to metallic Pb0 and oxidize I-minus to I2 or I3-minus in the perovskite layers.
06:24Subsequently, MA plus undergoes deprotonation, producing CH3 and H2 and HI gases, and ultimately leaving behind PbI2.
06:36In summary, photocatalytic reactions occur at the interface, chemically decomposing the perovskite layer.
06:46UV light-induced oxygen vacancies in TiO2 throw photocatalysis leading to the formation of PbI2 and the breakdown of organication,
07:00ultimately degrading the stability of the device.
07:10This slide explains the photo-induced degradation mechanism in perovskite solar cells.
07:16Figure A and B show the change in the Pb4F XPS spectra over a period of 0 to 76 hours under dark conditions and white light illumination respectively.
07:34In A, under dark conditions, the Pb4F XPS remains largely unchanged over time and the Pb2 plus state is stably maintained.
07:50This indicated that in the absence of light, reduction of lead or structural change occurs minimally.
08:00In contrast, B shows a gradual increase in the Pb0 peak around 137 EV as time progresses under white light.
08:16This suggests that light exposure promotes the reduction of Pb2 plus 2 metallic Pb0, likely due to halite ion loss and lead aggregation within the perovskite structure.
08:33Figure C presents the Pb0 concentration over time.
08:39While the concentration remains nearly constant in the dark, it increases noticeably under white light illumination.
08:51Moreover, the concentration of Pb0 is higher at room temperature than at low temperatures indicating that photo-induced degradation is more severe at higher temperatures even under the same lighting condition.
09:11Figure C shows the change in the chemical composition of each element over time under white light illumination.
09:23The intensity of the I3D and N1S peaks gradually decrease while the Pb0 signal continuously increases.
09:35This indicates that the decomposition reaction occurs within the perovskite layer under light exposure leading to the formation of metallic lead.
09:47Figure E presents a kinetic analysis of the decomposition reaction occurring in perovskite materials under illumination.
09:59The degradation process proceeds in two sequential steps.
10:07Step 1 is FAPBi3 decomposes into Pb2 and Fai.
10:15Step 2 is the resulting Pb2 further decomposes into Pb0 and I2.
10:22As a result, the light absorbing layer gradually disappears and metallic lead residue remains signifying reversible degradation.
10:38The comparison of the light constants between the two steps reveals that the second step proceeds significantly faster.
10:51This suggests that while the first reaction is highly temperature dependent, the second is mainly driven by light and show little dependence or temperature.
11:05In conclusion, photo-induced degradation occurs as light acceleration rate, chemical reaction rate, ultimately leading to the structural decomposition of the perovskite observer layer.
11:23This slide explains the defects in this degradation mechanism in perovskite solar cells.
11:30On the left side, we see an illustration of an idle crystal structure.
11:41However, in reality, various types of defects are generated due to fabrication processes, compositional imbalance or external stimuli.
11:59Defects are generally classified into point defects and extended defects.
12:06Point defects include vacancies, interstitial and anti-site defects where ion leave their original position or occupy incorrect sites.
12:18These defects cause charge imbalance and local electric field distortion.
12:26Extended defects occur across multiple disciplines and include 1D dislocations, 2D grain boundaries and 3D precipitates.
12:39Figure A and B defects.
12:40Figure A and B defects Schottky and Franco defects, which create vacancies and interstitial that facilitate the migration of halide ion or organications within the lattice.
13:01Figure C and C and D show degradation caused by lattice distortion.
13:08Charger accumulation around defects generate coulombic interactions causing the lattice to bend or twist.
13:20Impurities can introduce local stress and chemical inhomogeneity, further destabilizing the structure.
13:30In E, external pressure or stacking thoughts resulting in localized lattice softening or deformation.
13:42Figure F highlights the grain boundary region where a high concentration of defects creates fast ion migration pathways.
13:55In E, external pressure or ion accumulation in this region leads to non-uniform internal charge distribution.
14:05Lastly, GE illustrates how piezoelectric effects can generate in homogeneous internal electric fields and cause stress accumulation in the lattice.
14:20This promotes the growth of extended defects, eventually leading to mechanical weakening of the device.
14:30This slide explains ion migration in perovskite materials.
14:36Ion migration refers to the movement or redistribution of halide ion ions and organications within the perovskite crystal driven by electric fields, heat or light exposure.
14:55The diagram on the right conceptually illustrates the ion migration mechanism and its resulting effects.
15:07In a underdog condition, internal electric fields exist within the device.
15:16This field drives electron toward the electron transport layer and hosts toward the whole transport layer.
15:27At the same time, ions such as halide ion ion or organications migrate along defective pathways forming an ionic electric field that opposes the internal field.
15:44This interaction leads to non-uniform potential distribution within the device.
15:53In B, under illumination, light generates electron hole pairs that move toward the electron transport layer and whole transport layer respectively.
16:07Photogenerate carriers enhance the mobility of ions causing them to migrate more actively and accumulate near interface.
16:24Initially, the internal electric field and the ionic field oppose each other, but over time, as ions redistribute interface potentials are reformed, altering the internal electric field.
16:47Because this ionic distribution process is slow, time-dependent behavior such as the light sucking effects, JV hysteresis, and slow open circuit voltage decay occurs, as shown in the diagram.
17:06These phenomena are considered key contributors to delayed electrical response and long-term stability degradation in perovskite solar cells.
17:24This slide explains the phenomenon of phase segregation.
17:29Phase segregation occurs when mixed halide perovskite were exposed to light, leading to the separation of the crystal into a region rich in either iodide or bromide.
17:44This phenomenon can be explained by three main models.
17:50First model is thermodynamic models.
17:56This model suggests that the mixed halide state is thermodynamically unstable and light exposure further destabilizes the free energy equilibrium, thereby driving phase segregation.
18:18The second model is the second model.
18:20The second model is polaron strain induced model.
18:23In this model, polaron formed by photo-generated electrons and holes induced local lattice distortions, which promote the segregation of halide ion into distinct phases.
18:39Last model is electric field driven model.
18:46This model proposed that electric field generated by charge-trapping and ionic defects within the perovskite promote the migration and redistribution of halide ions, ultimately leading to phase segregation.
19:06As a result of this segregation, the stability of the perovskite materials deteriorates, which negatively affects defective performance.
19:26This final slide causes lattice mismatch.
19:31In the perovskite solar cells, multiple thin film layers are sequentially deposited on the bottom electrode as shown in the diagram.
19:44When the lattice constants of the underlying substrate and the upper perovskite layer differ, strain is generated between the two layers.
19:58This phenomenon is referred to as lattice mismatch, as shown in the diagram on the right.
20:11In cases of large lattice mismatch, the grain film may develop twisted grain boundaries and cracks, leading to increased defects and chargely combination with the crystal structure.
20:29On the other hand, when the lattice match is good, the perovskite film grows uniformly with fewer defects, resulting in smoother charge transport and improved device stability.
20:51The equation at the bottom quantifies the degree of lattice mismatch.
21:01A larger delta value indicates a greater difference in lattice constants between the two layers,
21:13which correspond to higher internal stress and a greater tendency for defective formation.
21:25Thank you.
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