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.
Nanodiamonds (NDs) are versatile, broadly available nanomaterials with a set of features highly attractive for applications from biology over energy harvesting to quantum technologies. Via synthesis and surface chemistry, NDs...
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.
manufacturing techniques such as roll-toroll (R2R) production are based on slot-die coating, which is suited for fast, cheap, and high-throughput industrial production. [7] Besides coating and printing, additional processing steps such as UV-curing, drying, or annealing may be required. In particular, drying and annealing processes, often done by either hot air or infrared lamps, are limited to processing temperatures of up to 120°C in the case of plastic substrates such as polyethylene terephthalate (PET). [8,9] Since typical annealing times are in the range of several minutes, an oven must have a length corresponding to the feed rate of the substrate. For example, for a feed rate of only 10 m min -1 and a 5 min annealing time, it would be necessary to use an oven of 50 m in length. Of course, this puts high demands on the scale of the production line, which adds considerably to its costs. Flash lamp annealing (FLA), on the other hand, is ultra-short in time (just a few milliseconds) and can induce temperatures of several hundred degrees Celsius within the targeted layer while keeping the substrate at moderate temperatures due to limited heat transport within the layer stack. In this regard, FLA is a very interesting method for annealing materials during R2R organic photovoltaic processing.The light is generated by the xenon arc lamps using high voltage to decompose the inert gas within the lamp envelope. Then, the generated pulse energy, delivered in a short time and high-intensity pulse, is sufficient to cause sintering. In addition to the fact that the short processing time (of the order of a few milliseconds) guarantees high efficiency and productivity, the substrate does not Thermal annealing (TA) is one of the most used processing techniques for the fabrication of polymer solar cells. The method is not only used to dry solutionprocessed films but also for improving the electrical conductivity and the optical absorption of the materials after coating as films. Its use is questionable in combination with high throughput manufacturing techniques such as roll-toroll large-scale production since annealing times of several minutes already put up high demands on oven lengths. Furthermore, the commonly used flexible substrates are not compatible with high processing temperatures. Therefore, there is a need for more rapid treatment techniques, which do not negatively affect the plastic substrate. Herein, it is successfully demonstrated that flash lamp annealing (FLA) can be a valid alternative to TA. The FLA technique is applied at various pulse durations and thus energy doses to PEDOT:PSS and SnO 2 films used as charge extraction layers in conventional and inverted solar cells architectures. In combination with PM6:Y6 photoactive layer, the obtained device's performances are comparable or even better than the devices treated with the classical TA on a hotplate. In terms of energy efficiency, the FLA is clearly more efficient than the TA, even at the size of prototypes.
Diamond nanoparticles so‐called nanodiamonds (NDs) have recently experienced raising scientific interest due to interesting optical and electronic properties, nontoxicity, biocompatibility, and large surface area. Another significant feature of NDs is the versatility of the surface chemistry, where various functional groups can be attached. This provides an excellent platform for adjusting NDs properties and functions for many applications including in photovoltaic devices. Herein, high‐pressure high‐temperature (HPHT) NDs are tested as charge extraction material in organic solar cells using various surface chemistries: as‐received (HPHT ND‐ar), oxidized (HPHT ND‐O), and hydrogenated (HPHT ND‐O‐H) NDs. Despite the high work function values (≈5.3 eV) of HPHT ND‐ar and HPHT ND‐O, which make these materials normally suitable for hole extraction, devices made with them failed. In contrast, the work function decreases upon hydrogenation (≈4.5 eV) of the beforehand oxidized NDs, making them interesting for electron extraction. By employing such HPHT ND‐O‐H for electron extraction layers, PBDB‐T:ITIC‐based devices reach 77%, while PM6:Y6‐based devices reach even 85% of the performance when process on standard ZnO electron transport layers. Improvement of the film‐forming qualities of this new electron extraction material is expected to further improve the performance.
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