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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
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Image of FIG. 1.
FIG. 1.

(a) The schematic device structure of an inverted PSC with an ITO/TiOx/P3HT:PCBM/PEDOT:PSS/metal electrode, and the P3HT, PCBM, and TiOx chemical structures. (b) Energy level diagram of the inverted PSC. (c) UV-vis absorption spectra of the TiOx, P3HT, and PCBM films. (d) AFM topographic images (5-μm × 5-μm) of the TiOx films on the ITO substrate.

Image of FIG. 2.
FIG. 2.

The J-V characteristics of I-PSCs. (a) The effect of white light on the recovery of the kink shape. (b) The effect of light irradiation at different wavelengths (i.e., red, green, blue, and UV light). (c) The effect of UV irradiation time. (d) The changes in efficiency, FF, (inset) Voc, and Jsc with UV irradiation time.

Image of FIG. 3.
FIG. 3.

(a) The schematic system of EIS measurement. The ITO/TiOx/Au structure was measured for impedance analysis. (b) The Bode plot and (c) Nyquist plot of ITO/TiOx/Au measured by EIS before and after UV irradiation. An equivalent circuit (inset) corresponding with the EIS results is also shown.

Image of FIG. 4.
FIG. 4.

(a) The WF variations of the TiOx layer with increasing UV exposure time. (b) High binding region of UPS spectra of bare ITO, ITO/TiOx (w/o, w/UV), and P3HT:PCBM film.

Image of FIG. 5.
FIG. 5.

(a) Jphoto response of the TiOx layer with UV on/off cycles and schematic device structure (inset). The dotted line shows the input signal during UV light activation and deactivation. (b) Investigation of the photocurrent saturation time with continuous UV irradiation. The trap site filling rate was gradually decreased and saturated after 10 min of UV irradiation.

Image of FIG. 6.
FIG. 6.

(a) The energy diagram of the ITO/TiOx interface before UV irradiation. The EB between ITO and TiOx hinders the charge transport of the device. Here, qΦITO, qXTiOx, and EF° represent the WF of ITO and the LUMO and Fermi level of the TiOx layer, respectively. There are many trap sites between the LUMO and EF° of TiOx. (b) The energy diagram of the ITO/TiOx composite after UV irradiation. The width of EB became narrow after UV irradiation, which results in the tunneling of charges through the ITO/TiOx interface. The WF of TiOx (qΦ°TiOx) before UV irradiation changed to the value of qΦ′TiOx after UV irradiation, which resulted in a change in the WF difference (ΔE) between ITO and TiOx from ΔE° to ΔE′.


Generic image for table
Table I.

Photovoltaic parameters of I-PSCs irradiated with white light at different wavelengths (i.e., red, green, blue, and UV) and for different UV irradiation times.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Light-soaking issue in polymer solar cells: Photoinduced energy level alignment at the sol-gel processed metal oxide and indium tin oxide interface