Processing Additives for Improved Efficiency from Bulk Heterojunction Solar Cells

Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California 93106, USA.
Journal of the American Chemical Society (Impact Factor: 12.11). 04/2008; 130(11):3619-23. DOI: 10.1021/ja710079w
Source: PubMed


Two criteria for processing additives introduced to control the morphology of bulk heterojunction (BHJ) materials for use in solar cells have been identified: (i) selective (differential) solubility of the fullerene component and (ii) higher boiling point than the host solvent. Using these criteria, we have investigated the class of 1,8-di(R)octanes with various functional groups (R) as processing additives for BHJ solar cells. Control of the BHJ morphology by selective solubility of the fullerene component is demonstrated using these high boiling point processing additives. The best results are obtained with R = Iodine (I). Using 1,8-diiodooctane as the processing additive, the efficiency of the BHJ solar cells was improved from 3.4% (for the reference device) to 5.1%.

76 Reads
  • Source
    • "Different fabrication/processing procedures can lead to substantially different film morphologies even when the same active materials are used. These will be detailed in Section 3. Blends of solvents, the use of additives , manual manipulation of the deposition temperature and the creation of a solvent saturated atmosphere are some of the strategies most commonly used in order to obtain a better control of the film drying process and manipulate the resulting bulk-in morphology [11] [12] [13] [14] [15] [16] [17] [18]. In this way, it is possible to achieve ideal spatial distributions of connected electron and hole favorable domains with sizes in the order of the exciton diffusion length that guarantee efficient charge separation and transport. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Organic photovoltaics will become 30 years old relatively soon. In spite of the impressive development achieved throughout these years, especially in terms of reported power conversion efficiencies, there are still important technological and fundamental obstacles to circumvent before they can be implemented into reliable and long-lasting applications. Regarding device processing, the synthesis of highly soluble polymeric semiconductors first, and fullerene derivatives then, was initially considered as an important breakthrough that would definitely change the fabrication of photovoltaics once for all. Nowadays, the promise of printing solar cells by low-cost and high throughput mass production techniques still stands. However, the potential and the expectation raised by this technology is such that it is considerably difficult to keep track of the most significant progresses being now published in different and even monographic journals. There is therefore the need to compile the most remarkable advances in well-documented reviews than can be used as a reference for future ideas and works. In this letter, we review the development of polymeric solar cells from its origin to the most efficient devices published to date. After analyzing their fundamental limits, we separate these achievements into three different categories traditionally followed by the scientific community to push devices over 10% power conversion efficiency: Active materials, strategies -fabrication/processing procedures- that can mainly modify the active film morphology and result in improved efficiencies for the same starting materials, and all the different cell layout/architectures that have been used in order to extract as high photocurrent as possible from the Sun. The synthesis of new donors and acceptors, the use of additives and post-processing techniques, buffer interlayers, inverted and tandem designs are some of the most important aspects that are in detailed reviewed in this letter. All have equally contributed to develop this technology and leave it at doors of commercialization.
    Organic Electronics 04/2015; 19. DOI:10.1016/j.orgel.2015.01.014 · 3.83 Impact Factor
  • Source
    • "This conclusion is supported by Cho et al. [9], who showed that the ODT was not completely removed from the active layer films by placing them in high vacuum ($10 À6 Torr). Residual ODT left in the active layer will selectively dissolve the C 71 -PCBM component, as the PCPDTBT is less soluble in ODT [6] and will lead to increased aggregation and a reduction in the connectivity of C 71 -PCBM percolation networks, thus limiting the amount of charge that can be extracted from the active layer. Therefore, in order to have stable PCPDTBT:C 71 -PCBM devices made using ODT, it might be necessary to remove the ODT after processing. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The synthesis was conducted by Prof Masaki Horie (Tsing Hua University/University of Manchester) using 'Direct-arylation,' outlined in Figure 1. This provides an option for synthetic scale-up and is particularly significant as the Suzuki and Stille synthesis reactions inherently possess a number of problematic stages: time-consuming processing of the monomer units; impurities which can arise during the synthesis as the organostannyl monomers are difficult to purify; and finally, that the organostannyls used in Stille coupling are highly toxic. Fig. 1 Synthetic scheme for PCPDTBT Outdoor monitoring of PCPDTBT modules PCPDTBT modules were fabricated on glass-ITO substrates and tested outdoors in Winter 2013. Modules were fabricated with dimensions 5cmx5cm and mounted onto a board at 36° due South (the optimum position for a module in Bangor, North Wales to maximise annual yield). The mounting board has OPV modules on it (one with a PT100 temperature sensor) and an IMT Solar silicon reference cell for irradiance measurements (Fig 5). Data was monitored using SMUs and a wireless weather station, which provides meteorological data (temperature, irradiance, UV, humidity, rainfall, wind speed/direction), recorded every minute. Fig. 5: OPV module and outdoor monitoring setup. Module performance was measured every minute and tests are ongoing to understand degradation mechanisms. Fig. 6 shows the performance on two days: 10 th December is a relatively sunny day in Winter and the 11 th represents a cloudy with high diffuse content of irradiated light. The OPV performance appears to track the in-plane irradiance very closely, but also the performance of silicon modules, which are positioned close by (see Fig. 5). This is to be anticipated as the top surface of both modules possess similar optical properties. Fig. 6: Comparison of OPV module performance on 'sunny' and 'cloudy' days in December 2013. Summary PCPDTBT:PCBM organic photovoltaics are evaluated for long term performance and the effect of using 1,8-octanedithiol (ODT) processing additive is studied. The results show ODT is detrimental to the long term performance of the cells and AFM topography scans, as well as fill factor measurements, show that a greater change in morphology is observed for devices fabricated with ODT when irradiated under a light soaker continuously. Initial results for studying PCPDTBT:PCBM modules in outdoor conditions are reported. Acknowledgments
    Next Generation Materials, RSC Conference, 15thJanuary 2014, London, UK.; 01/2015
  • Source
    • "One strategy to control the morphology in donor/acceptor mixtures involves adding a solvent additive, generally at 0.1–10% of the solvent volume [16] [25]. Solvent additives studied include 1,8-diiodooctane (DIO), 1-chloronaphtha- lene, 1,8-octanedithiol, and alkylthiophenes. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The development of non-fullerene electron acceptors for organic photovoltaics is gaining interest, as they offer the promise to overcome the light harvesting and energy tunability limitations of fullerenes. However, to fully take advantage of alternative acceptors, we must identify and achieve the needed morphologies within the active layer to maximize device performance. Here we demonstrate that the microstructure in the active layer of optimized poly(3-hexylthiophene)/naphthalene diimide devices resembles that of poly(3-hexylthiophene)/fullerene mixtures. Previously, we have reported on the synthesis of 2,6-dialkylaminonaphthalene diimides and found that the best performance was obtained with N,N'-di((thiophen-2-yl)methyl)-2,6-di(N-cyclohexylamino)-1,4,5,8-naphthalenetetracarboxydiimide (RF1). In this article, we show that suppressing the crystallization of both the donor and acceptor through the addition of 0.2% 1,8-diiodooctane (DIO) to the casting solution leads to finer morphologies in the active layer and a two-fold enhancement in the device efficiencies. Nevertheless, further increasing the DIO content of the casting solution leads to lower photocurrents and power conversion efficiencies, even though the morphology appears similar by energy-filtered TEM. We hypothesize that higher DIO content breaks up small RF1 aggregates, leading to suppression of charge separation. Continued development of novel non-fullerene acceptors must therefore take into consideration the balance between crystallization and aggregation of donors and acceptors for optimal performance.
    Organic Electronics 11/2014; 15(11-11):3384-3391. DOI:10.1016/j.orgel.2014.09.021 · 3.83 Impact Factor
Show more

Similar Publications


76 Reads
Available from