Device Performance and Lifetime of Polymer:Fullerene Solar Cells with UV‐Ozone‐Irradiated Hole‐Collecting Buffer Layers

Abstract

We report the influence of UV-ozone irradiation of the hole-collecting buffer layers on the performance and lifetime of polymer:fullerene solar cells. UV-ozone irradiation was targeted at the surface of the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layers by varying the irradiation time up to 600 s. The change of the surface characteristics in the PEDOT:PSS after UV-ozone irradiation was measured by employing optical absorption spectroscopy, photoelectron yield spectroscopy, and contact angle measurements, while Raman and X-ray photoelectron spectroscopy techniques were introduced for more microscopic analysis. Results showed that the UV-ozone irradiation changed the chemical structure/composition of the surface of the PEDOT:PSS layers leading to the gradual increase of ionization potential with irradiation time in the presence of up-and-down variations in the contact angle (polarity). This surface property change was attributed to the formation of oxidative components, as evidenced by XPS and Auger electron images, which affected the sheet resistance of the PEDOT:PSS layers. Interestingly, device performance was slightly improved by short irradiation (up to 10 s), whereas it was gradually decreased by further irradiation. The short-duration illumination test showed that the lifetime of solar cells with the UV-ozone irradiated PEDOT:PSS layer was improved due to the protective role of the oxidative components formed upon UV-ozone irradiation against the attack of sulfonic acid groups in the PEDOT:PSS layer to the active layer.

A Pronounced Dispersion Effect of Crystalline Silicon Nanoparticles on the Performance and Stability of Polymer:Fullerene Solar Cells

“…As shown in Figure , the J SC value of the control device was slowly decreased as the illumination time increased. This decreasing trend is in agreement with our previous work. ,, Interestingly, the device with 2 wt % SiNP-OA showed almost similar J SC trend with the control device, whereas the J SC value of the device with 2 wt % SiNP was quickly dropped as the illumination time increased. The FF value was also significantly decreased for the device with 2 wt % SiNP, but the device with 2 wt % SiNP-OA showed better FF value than the control device.…”

All-polymer solar cells with bulk heterojunction nanolayers of chemically doped electron-donating and electron-accepting polymers

“…In addition, it is a concern that the long-term stability of polymer:fullerene solar cells might be affected by continuous aggregation/ crystallization of fullerene derivatives (molecules), even in the solid state matrix of electron-donating polymers, under solar light illumination for a long time. [27][28][29][30][31][32] In this context, all polymer BHJ (polymer:polymer) solar cells have been studied but their efficiencies are still inferior to those of polymer:fullerene solar cells. 6,[33][34][35][36][37][38][39] The reason why so low efficiency in polymer:polymer solar cells can be mainly attributed to the poorly optimized morphology for charge percolation owing to the intrinsic nature of polymers that have long chains compared to soluble fullerenes that easily undergo aggregation/crystallization.…”

Strong addition effect of charge-bridging polymer in polymer:fullerene solar cells with low fullerene content

“…Several reasons have been suggested for the low stability of polymer:fullerene solar cells, including the corrosion effect caused by the acidity of holecollecting buffer layers, the interfacial degradation between active layers and metal electrodes, the light-induced degradation of conjugated polymers (excited states), the gradual demixing between conjugated polymers and soluble fullerenes, etc. [16][17][18][19][20][21][22][23][24] Among these reasons, both the degradation of conjugated polymers and the demixing between conjugated polymers and fullerenes (morphological instability) under continuous solar light illumination may be the most challenging to overcome in order to secure the stability of polymer-based solar cells.…”