Light-soaking issue in polymer solar cells: Photoinduced energy level alignment at the sol-gel processed metal oxide and indium tin oxide interface

Kim, Junghwan; Kim, Geunjin; Choi, Youna; Lee, Dong Kun; Park, Sung Heum; Lee, Kwanghee

doi:10.1063/1.4728173

Cited by 115 publications

(110 citation statements)

References 31 publications

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“…Therefore, the interface charge transport may become the main factor that influences cell performance. In inverted solar cells that contain sol-gel titanium oxide as an electron collection layer, a light soaking effect that cell performance improves gradually with an increase in light irradiation time has often been observed [10][11][12][13][14][15][16] . Although this mysterious phenomenon is now well known, there is not necessarily satisfactory explanation for the mechanism.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Investigation into the Light Soaking Effect Observed in Inverted Polymer Solar Cells Containing Chemical Bath Deposited Titanium Oxide

Kawamata¹,

Yano²,

Yamaguchi³

et al. 2015

J. Phys. Chem. C

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In the glass-indium tin oxide (ITO) / titanium oxide (TiO x ) / regioregular poly(3-hexylthiophene) (P3HT) : [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) / poly(3,4-ethylenedioxylenethiophene) : poly(4-styrene sulfonic acid) (PEDOT:PSS) / Au cell (TiO x cell), which contains amorphous titanium oxide prepared by chemical bath deposition and dried at 150 °C, a light soaking effect has been observed upon irradiation with white light.In contrast, in ITO / titanium oxide (TiO 2 ) / P3HT:PCBM / PEDOT:PSS / Au cell (TiO 2 cell), which contains anatase titanium oxide prepared by heat treatment at 450 °C, the maximum power conversion efficiency was obtained just after irradiation with white light. The number of P3HT + cation radicals in the quartz-ITO/TiO x and TiO 2 /P3HT:PCBM substrates was estimated by ESR measurements at room temperature upon irradiation with white light. They increased gradually with an increase in irradiation time for the TiO x substrate, but increased only slightly just after light irradiation for the TiO 2 substrate. Upon irradiation with UV-cut light, the performance of the TiO x cell was inferior to that of the TiO 2 cell. This could be related to the resistances of the P3HT:PCBM layers which were estimated by alternating-current impedance spectroscopy. The resistance of the P3HT:PCBM layer in the TiO x cell was much larger than that in the TiO 2 cell, though the difference between the two cells was merely heat treatment temperature of titanium oxide films using as electron collection layers. That is, the concentration of photocarriers in the P3HT:PCBM of the TiO x 2 cell was significantly less than that in the P3HT:PCBM of the TiO 2 cell. From these experimental results, the light soaking effect could be reasonably explained by assuming the existence of charge recombination centers in the TiO x near the TiO x /P3HT:PCBM interface.

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Section: Introductionmentioning

confidence: 99%

Mechanistic Investigation into the Light Soaking Effect Observed in Inverted Polymer Solar Cells Containing Chemical Bath Deposited Titanium Oxide

Kawamata¹,

Yano²,

Yamaguchi³

et al. 2015

J. Phys. Chem. C

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“…[3][4][5][6][7] One of the fundamental issues is the light-soaking phenomenon with respect to UV-light irradiation, which has been commonly observed in IOSCs with electron-collecting layers such as TiO x . 2,[8][9][10][11][12][13][14][15] Although high-temperature annealing treatments on the TiO x layer can prevent the phenomenon, such treatments are undesirable for low-temperature device fabrication using flexible plastic substrates. 15 Additionally, long-term UV-light irradiation on IOSCs can cause device degradation.…”

mentioning

confidence: 99%

Direct observation of UV-induced charge accumulation in inverted-type polymer solar cells with a TiOx layer: Microscopic elucidation of the light-soaking phenomenon

Son

Takahashi

Marumoto

2016

Applied Physics Letters

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The mechanism of light-soaking phenomenon in inverted-type organic solar cells (IOSCs) with a structure of indium-tin-oxide/TiOx/P3HT:PCBM/Au was studied by electron spin resonance (ESR) spectroscopy. Charge accumulation in the cell during UV-light irradiation was observed using ESR, which was clearly correlated with the light-soaking phenomenon. The origin of the charge accumulation is clarified as holes that are deeply trapped at p-type P3HT polymer-chain ends with bromine after hole transfer from the band excitation in the TiOx layer. The holes are considered to be electrostatically attracted to trapped electrons in the TiOx layer after the band excitation. These accumulated charges are the origin of the light-soaking phenomenon. Our results strongly suggest that passivation of the residual OH groups in the TiOx layer is needed to avoid the light-soaking phenomenon by preventing electron trappings, a step that is indispensable in the operation of highly stable IOSCs without UV-light irradiation based on a low-cost and low-temperature device fabrication process using flexible plastic substrates.

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“…[32][33][34][35][36][37] Some of these trap states, close to the ITO/ZnO, could be filled up during the light-soaking illumination. 19,22 On the other hand, the trap states, close to the ZnO/P3HT:PCBM, could change the induced interfacial dipoles. 23,24 Presented data do not consider which interface (ITO/ZnO or ZnO/P3HT:PCBM) plays the key role in the lightsoaking effect but highlight the need for taking into account the LS effect in the analysis.…”

Section: Changes In Magnitude Of the Light-soaking Effect During The mentioning

confidence: 99%

“…In the first case, the filling of trap states upon illumination decreases the work function of the ETL, which reduces the potential barrier and thus improves the extraction of electron through the ITO/metal-oxide interface. 19,22 In the second case, the key role in the light-soaking effect plays the interfacial dipole between the metal-oxide/organic interface. [23][24][25] Sometimes the devices should be stimulated under solar simulator for at least few minutes (∼10 min) at the 1000-W∕m 2 illumination intensity, for saturation of their photovoltaic properties.…”

Section: Introductionmentioning

confidence: 99%

Significance of light-soaking effect in proper analysis of degradation dynamics of organic solar cells

2016

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Abstract. One of the issues in the organic solar-cell technology that needs attention before mass production is its low long-term stability. These devices need often to be exposed to the light to improve their photovoltaic properties. This effect, known as light soaking, is the cause of challenges related to correct measurements and proper determination of the device lifetime. Lifetime determination and investigation of failure mechanisms of solar-cell devices require reliable measurement approaches. This paper presents the systematic studies on proper analysis of degradation dynamics of organic solar cells (OSCs) taking into account the light-soaking effect.Five groups of organic solar-cell annealed at various conditions (110°C to 170°C and nonannealed) were under investigation for 100 days. Measurement procedure for proper investigation of light-soaking effect is proposed. Solar-cell efficiency improvement, due to light-soaking effect, in range 8% to 27% was observed for as fabricated devices. After 100 days of study, the light soaking-related efficiency improvement increased up to over 100% of initial efficiency. Device lifetimes strongly depend on measurement methods, which were applied. Our results show the importance of taking into account the changes in magnitude of the light-soaking effect in measurements and degradation studies of OSCs. © The Authors. Published by SPIE under aCreative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Light-soaking issue in polymer solar cells: Photoinduced energy level alignment at the sol-gel processed metal oxide and indium tin oxide interface

Cited by 115 publications

References 31 publications

Mechanistic Investigation into the Light Soaking Effect Observed in Inverted Polymer Solar Cells Containing Chemical Bath Deposited Titanium Oxide

Mechanistic Investigation into the Light Soaking Effect Observed in Inverted Polymer Solar Cells Containing Chemical Bath Deposited Titanium Oxide

Direct observation of UV-induced charge accumulation in inverted-type polymer solar cells with a TiOx layer: Microscopic elucidation of the light-soaking phenomenon

Significance of light-soaking effect in proper analysis of degradation dynamics of organic solar cells

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