Here, we studied the influence of pre-and post-thermal annealing on the performance of polymer:fullerene bulk heterojunction solar cells using the conventional architecture, comprising a conjugated polymer, namely, poly(3-hexylthiophene-2,5-diyl) (P3HT) and a fullerene derivative [6,6]-phenyl-C60-butyric acid methyl ester (PC 60 BM) as a photoactive layer. The nonannealed active layer device exhibited a power conversion efficiency of <1%, which was significantly lower than the pre-and post-annealed devices. To investigate the impact of pre-and post thermal annealing on the natural morphological state of the polymer, regiorandom (P3HT-I) and regioregular (P3HT-II) type P3HT were compared in photoactive layers. In general, P3HT-I is amorphous, whereas P3HT-II is semi-crystalline. Changes in solar cell performance were associated with changes in carrier extraction efficiencies influenced by the annealing conditions. The charge photogeneration processes were investigated using spectroscopic techniques, including electroluminescence, steady-state, and time-resolved photoluminescence spectroscopy. Finally, to explore the morphological changes upon annealing, atomic force microscopy and electroluminescence imaging measurements were performed on films and solar cells, respectively. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

As the device performance and stability of polymer solar cells strongly depend on the interfacial charge extraction layers, the hole transport layer (HTL) properties are crucial. Furthermore, unfavorable interactions with the electrode or the photoactive layer should be screened and prevented. Organic solar cells of conventional architecture by varying the HTL material and layer stack systematically between PEDOT:PSS and a sol–gel‐derived tungsten oxide (WO3) are investigated. The impact of various HTLs in the solar cells is investigated by optical and electrical characterization. Interestingly, a triple‐layer WO3/PEDOT:PSS/WO3 configuration results in the best device performance specifically compared with the use of pristine WO3 and pristine PEDOT:PSS hole extraction layers. The triple layer also shows an increased reproducibility in the lifetime, which, combined with the improvement in the efficiency, can be the keys for expectable revenue.

mask was applied to define the solar cell's active area of 0.42 cm 2 during evaporation. Finally, all samples were encapsulated by epoxy-based UV-curing glue under glass before testing.

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