Improved Performance in Polymer Solar Cells Using Mixed PC<sub>61</sub>BM/PC<sub>71</sub>BM Acceptors

Ko, Seo Jin; Lee, Wonho; Choi, Hyosung; Walker, Bright; Yum, Seungjib; Kim, Seongbeom; Shin, Tae Joo; Woo, Han Young; Kim, Jin Young

doi:10.1002/aenm.201401687

Cited by 66 publications

(47 citation statements)

References 25 publications

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“…This is in agreement with the experimentally observed correlation between optimal fill factor and optimal PCE. 6,7,17 Second, in Figure 8 the overall optimal PCE is still located on the binary line, where both donors have the same HOMO and LUMO. This reiterates the superiority of a single optimal bandgap provided the absorption is sufficiently broad.…”

Section: Selecting Optimal Donor Materials and Compositionsmentioning

confidence: 99%

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Open circuit voltage and efficiency in ternary organic photovoltaic blends

Felekidis

Wang

Kemerink

2016

Energy Environ. Sci.

104

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Organic bulk heterojunction solar cells based on ternary blends of two donor absorbers and one acceptor are investigated by experiments and modeling. The commonly observed continuous tunability of the open circuit voltage with donor1:donor2 ratio can quantitatively be explained as quasi-Fermi level splitting due to photocreated charges filling a joint density of states that is broadened by Gaussian disorder. On this basis, a predictive model for the power conversion efficiency that accounts for the composition-dependent absorption and the shape of the current-voltage characteristic is developed. When all other parameters, most notably the fill factor, are constant, we find that for state-of-the-art absorbers, having a broad and strong absorption spectrum, ternary blends offer no advantage over binary ones. For absorbers with a more narrow absorption spectrum ternary blends of donors with complementary absorption spectra, offer modest improvements over binary ones. In contrast, when, upon blending, transport and/or recombination kinetics are improved, leading to an increased fill factor, ternaries may offer significant advantages over binaries. Broader contextSolar cells based on blends of organic semiconductors almost routinely reach power conversion efficiencies (PCE) in the 10% range. One of the strategies that has been proposed to push this limit further upward is the use of so-called ternary blends in which two instead of one absorbing donor material is blended with the electron acceptor. Systematic improvement of PCE by ternary blending has been reported. Despite the experimental success, the current understanding of both the PCE enhancement and the underlying puzzling tunability of the open circuit voltage Voc is limited and essentially qualitative. In this contribution we develop and validate a quantitative and predictive framework for both the Voc and PCE of ternary organic solar cells, which allows us to propose design rules. In contrast to current wisdom, we demonstrate that PCE enhancement in ternary blends hardly results from optimizing the overlap with the solar spectrum but predominantly from synergetic improvement of the charge transport and recombination kinetics. The model can be easily extended to include more detail and will allow other researchers to upfront evaluate the photovoltaic potential of 'any' ternary material combination. 10 On the same basis Savoie et al. proposed an empirical expression for Voc as a current-weighted average of the two sub-systems and used this to estimate a maximal theoretical PCE (of 13%) for varying donor bandgaps. 11 Apart from lacking a formal basis, there are two problems with the parallel junction picture. First, it relies on a specific morphology in the active layer that allows different regions to act as independent binary cells that are electrically decoupled. Even if a fortunate morphology would lead to the presence of two (hole-) percolating networks that are electrically isolated from each other, the presence of metal contacts does unavoidably enforce...

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Section: Selecting Optimal Donor Materials and Compositionsmentioning

confidence: 99%

“…In practice, especially the fill factor can depend significantly on composition, as e.g. in References 6,7,17 , leading to optimal ternary compositions. Where this is not the case, e.g.…”

Section: Selecting Optimal Donor Materials and Compositionsmentioning

confidence: 99%

Open circuit voltage and efficiency in ternary organic photovoltaic blends

Felekidis

Wang

Kemerink

2016

Energy Environ. Sci.

104

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“…24,30,31 Therefore, the majority of studies on ternary solar cells have focused on multi-polymer donor:acceptor blends. 19,23,[27][28][29] However, the mixing of two polymers is more complicated due to both a lack of entropic driving force for mixing, and the potential for strong intermolecular attractions between polymer chains. 32 Therefore, a ternary approach, wherein small molecule acceptors are mixed in a donor:multi-acceptor blend (D:A1:A2, where D is donor polymer, A1 is the primary acceptor and A2 is a second acceptor), has the potential to offer morphological advantages.…”

Section: Introductionmentioning

confidence: 99%

Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells

et al. 2016

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Technological deployment of organic photovoltaic modules requires improvements in device light-conversion efficiency and stability while keeping material costs low. Here we demonstrate highly efficient and stable solar cells using a ternary approach, wherein two non-fullerene acceptors are combined with both a scalable and affordable donor polymer, poly(3-hexylthiophene) (P3HT), and a high efficiency, low band-gap polymer in a single-layer bulk-heterojunction devices. The addition of a strongly absorbing small molecule acceptor into a P3HT-based non-fullerene blend increases the device efficiency up to 7.7 ± 0.1% without any solvent additives. The improvement is assigned to changes in microstructure that reduces charge recombination and increases the photovoltage, and to improved light harvesting across the visible region. The stability of P3HT-based devices in ambient conditions is also significantly improved relative to polymer:fullerene devices. Combined with a low band gap donor polymer (PBDTTT-EFT, also known as PCE10), the two mixed acceptors also lead to solar cells with 11.0 ± 0.4% efficiency and a high open-circuit voltage of 1.03 ± 0.01V.Currently, the materials used in organic photovoltaics (OPV) are dominated by fullerene acceptors in combination with low band gap donor polymers which typically require complex and multi-step syntheses. [1][2][3][4][5] However, the commercialization of OPV requires the availability of inexpensive materials in large quantities such as poly(3-hexylthiophene) (P3HT). P3HT is readily scalable via flow or micro-reactor synthesis, even using 'green' solvents, whilst retaining a high degree of control over molecular weight and regioregularity. 6 The P3HT:60PCBM blend exhibits one of the most robust microstructures within OPV. [7][8][9] However, it has a limited open-circuit voltage (Voc) and short-circuit current (Jsc) in photovoltaic devices. 10 We have recently shown that solar cells using an alternative small molecule non-fullerene acceptor (NFA), IDTBR, when mixed with P3HT, can achieve power conversion efficiencies of up to 6.4%. 11 These results have revived interest in the use of P3HT for high performing devices and non-fullerene acceptors. [12][13][14][15][16][17][18] The combination of stability, cost and performance for P3HT:NFA devices, make them a compelling choice for commercialization of OPV compared to devices using fullerenes, for which the high costs and energy involved are prohibitive for large scale production.Recently, multi-component heterojunctions (ternary or more) have emerged as a promising strategy to overcome the power conversion efficiency (PCE) bottleneck associated with binary bulk-heterojunction (BHJ) solar cells. 3,4,[19][20][21][22][23]24 However, simultaneous increase in the Voc, Jsc and FF is a challenge in the ternary approach because of the trade-off between photocurrent and voltage. 23,25,26 Reports show ternary blends using fullerene acceptors, where the Voc is increased using a second acceptor (A2) with a higher electron affin...

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“…PC 61 BM and PC 71 BM was chosen due to their desired energy levels, high electron mobility and good solubility in most organic solvents [23][24][25][26]. The solar cells based on P3HT:PC 61 BM and PCDTBT:PC 71 BM were fabricated and characterized using current-voltage (I-V) characteristics.…”

Section: Introductionmentioning

confidence: 99%

Influence of donor–acceptor materials on the photovoltaic parameters of conjugated polymer/fullerene solar cells

Sharma

Singh

Arora

et al. 2015

J Mater Sci: Mater Electron

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Organic solar cells based on poly(3-hexylthiophene-2,5-diyl): [6, 6]-phenyl-C61-butyric acid methyl ester are the most researched solar cells, but still there is a need to achieve higher efficiency and better stability. The active layer blends of poly [N-9 00 -heptadeca-nyl-2,7-carbazole-alt-5,5-(4 0 ,7 0 -di-2-thienyl-2 0 ,1 0 ,3 0 -benzo-thiadiazole)]: [6, 6]-phenyl-C71-butyric acid methyl ester (PCDTBT:PC 71 BM) show a promise in this regard. In this work, PCDTBT:PC 71 BM thin films were prepared with different blend ratios and concentrations, and were characterized for optical and morphological properties. UVvisible spectral studies showed that the absorption decreases as the acceptor concentration in the blend increases. Atomic Force Microscopy studies showed that surface roughness increases with the increase in acceptor concentration. Optimization of the active layer was carried out by using different blend ratios and concentration to achieve better performance, and it was observed that the highest efficiency was obtained at the optimized blend ratio of 1:4 and a concentration of 12 mg/ml. Further, the variation observed in the open circuit voltage with blend ratio has been explained by the disorder induced tail states in the energy levels of donor and acceptor materials.

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Improved Performance in Polymer Solar Cells Using Mixed PC₆₁BM/PC₇₁BM Acceptors

Cited by 66 publications

References 25 publications

Open circuit voltage and efficiency in ternary organic photovoltaic blends

Open circuit voltage and efficiency in ternary organic photovoltaic blends

Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells

Influence of donor–acceptor materials on the photovoltaic parameters of conjugated polymer/fullerene solar cells

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Improved Performance in Polymer Solar Cells Using Mixed PC61BM/PC71BM Acceptors

Cited by 66 publications

References 25 publications

Open circuit voltage and efficiency in ternary organic photovoltaic blends

Open circuit voltage and efficiency in ternary organic photovoltaic blends

Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells

Influence of donor–acceptor materials on the photovoltaic parameters of conjugated polymer/fullerene solar cells

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Improved Performance in Polymer Solar Cells Using Mixed PC₆₁BM/PC₇₁BM Acceptors