Enhancement of VOC without Loss of JSC in Organic Solar Cells by Modification of Donor/Acceptor Interfaces

Zhong, Yufei; Tada, Akira; Izawa, Seiichiro; Hashimoto, Kazuhito; Tajima, Kazuo

doi:10.1002/aenm.201301332

Cited by 59 publications

(47 citation statements)

References 31 publications

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“…A tunable dipole layer, which consisted of an ultrathin ferroelectric polymer film and was inserted between the donor and the acceptor layers, can shift the relative energy levels of the donor and the acceptor, tune the LUMO offset between the donor and acceptor and hence increase the V OC . [181][182][183] In 2012, Yang et al chose a polyvinylidene fluoride (70%)-trifluoroethylene (30%) copolymer, P(VDF-TrFE), as the tunable dipole layer and inserted it between P3HT and PCBM layers, resulting in the V OC increase from 0.55 V to 0.67 V and two-fold increase in PCE, as compared to devices without aligning the dipole layer. In 2013, Zhong et al applied surfacesegregated monolayers (SSMs) of fluoroalkylated organic semiconductors, [6] -phenyl-C 61 -butyric acid 1H,1H-perfluoro-1-nonyl ester (FC 8 ), as the dipole layer at the D/A interface (Figure 12).…”

Section: Dipole Interlayermentioning

confidence: 98%

Layer‐by‐Layer Processed Organic Solar Cells

Wang

Zhan

2016

Advanced Energy Materials

104

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Layer‐by‐layer (LL) processes, i.e., sequential deposition of different active layers, are widely used in the fabrication of organic solar cells (OSCs). Recently, LL vacuum deposition and LL solution processes have attracted considerable attention. LL processing presents some advantages over the blend method: a) donor and acceptor layers can be easily and independently controlled and optimized; b) the charge carriers dissociated from excitons at the donor–acceptor interface are confined to each phase, so bimolecular recombination losses can be reduced; c) bilayer geometries enable an easier way for understanding the physical processes taking place at the donor–acceptor interface; d) desired vertical phase separation for charge extraction can be obtained through changing the sequence of donor and acceptor deposition. This report summarizes the recent developments of LL processed OSCs. The remaining problems and challenges, and the key research direction in near future are discussed.

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Section: Dipole Interlayermentioning

confidence: 98%

Layer‐by‐Layer Processed Organic Solar Cells

Wang

Zhan

2016

Advanced Energy Materials

104

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“…However, as the corresponding 6T/ DIP and DIP/C 60 cells exhibit much higher V OC 's (1.22 eV and 0.91 eV, respectively), the main effect probably comes from suppressed recombination between 6T and C 60 by the interlayer, similar to the application of wide-gap insulating interlayers as reported in literature. [43] An alternative mechanism to the formation of an energy cascade has recently been suggested in polymer-fullerene bulk hetero-junctions. [44] These authors have proposed that the presence of an intermixed interface with locally enhanced CT energy creates a driving force for charge separation without loss in V OC .…”

Section: Reducing the Driving Forcementioning

confidence: 99%

Energy Losses in Small‐Molecule Organic Photovoltaics

Linderl

Zechel

Brendel

et al. 2017

Advanced Energy Materials

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processible PV technology has recently appeared as well. [5] Comparing the different technologies in terms of PCE, which is specified as the product of the short-circuit current density j SC , the open-circuit voltage V OC and the fill factor FF divided by the incoming light intensity under standard AM 1.5G illumination conditions, OPVs can well compete with their inorganic counterparts in terms of j SC or, more precisely, the external quantum efficiency and also with minor trade-off in FF, but clearly suffer from lower V OC at a given energy gap E g of the light absorbing material. While this socalled bandgap-voltage offset can be as low as 0.3-0.4 eV in Si and GaAs [6] and only a little larger in perovskite cells, [7] OPV cells exhibit energy losses of at least 0.6 eV -in many cases, however, this offset can approach and even exceed 1 eV. [8] This is currently one of the main bottlenecks toward making OPVs competitive with inorganic PV cells.In this research news, we provide the required background information on the appearance of energy losses in OPV cells, by which we mean the difference between the equivalent of the optical gap and the measured open-circuit voltage that is frequently also denoted as voltage loss, and discuss recent progress toward better understanding their origin and strategies to reduce them. To keep focused, we will mainly address small molecules as active organic semiconductors, which are being processed into thin films by vacuum deposition techniques. Compared to frequently studied π-conjugated polymers, the synthesis of small molecules is more reproducible. Moreover, a rigorous purification of small molecules is easier, which gives the opportunity to reproducibly investigate well-defined systems. The application of vacuum deposition techniques prevents the use of solvents, which as a third component in wet chemical processing can strongly influence the morphology. [9] Thus, active layers of small molecules prepared by vacuum deposition methods mark a well-controlled model system for fundamental studies such as the origin of energy losses in OPV devices. However, we expect that most of the findings can be transferred to solution-processed OPVs as well, which have considerably higher complexity in terms of local morphology and phase behavior. Excitonic Organic Solar CellsIn order to properly address energy losses in OPVs it is useful to look at their working principles in more detail (see also [10] ).

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“…Organic solar cells (OSCs) based on bulk heterojunction (BHJ) structure are promising candidates for the generation of clean, affordable electricity owing to their low fabrication cost compared to inorganic solar cells [1,2]. Recent research efforts into the development of new donor-acceptor blends have led to a significant improvement in the power conversion efficiency (PCE) of OSCs, above 11% [3][4][5][6], which is gradually moving OSCs closer to commercialization.…”

Section: Introductionmentioning

confidence: 99%

Study of the Contributions of Donor and Acceptor Photoexcitations to Open Circuit Voltage in Bulk Heterojunction Organic Solar Cells

Yeboah

Singh

2017

Electronics

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Abstract:One of the key parameters in determining the power conversion efficiency (PCE) of bulk heterojunction (BHJ) organic solar cells (OSCs) is the open circuit voltage (V OC ). The processes of exciting the donor and acceptor materials individually in a BHJ OSC are investigated and are found to produce two different expressions for V OC s. Using the contributions of electron and hole quasi-Fermi levels and charge carrier concentrations, the two different V OC expressions are derived as functions of the energetics of the donor and acceptor materials and the photo-generated charge carrier concentrations, and calculated for a set of donor-acceptor blends. The simultaneous excitation of both the donor and acceptor materials is also considered and the corresponding V OC , which is different from the above two, is derived. The V OC calculated from the photoexcitation of the donor is found to be somewhat comparable with that obtained from the photoexcitation of the acceptor in most combinations of the donor and acceptor materials considered here. It is also found that the V OC calculated from the simultaneous excitations of donor and acceptor in BHJ OSCs is also comparable with the other two V OC s. All three V OC s thus derived produce similar results and agree reasonably well with the measured values. All three V OC s depend linearly on the concentration of the photoexcited charge carriers and hence incident light intensity, which agrees with experimental results. The outcomes of this study are expected to help in finding materials that may produce higher V OC and hence enhanced PCE in BHJ OSCs.

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Enhancement of V_OC without Loss of J_SC in Organic Solar Cells by Modification of Donor/Acceptor Interfaces

Cited by 59 publications

References 31 publications

Layer‐by‐Layer Processed Organic Solar Cells

Layer‐by‐Layer Processed Organic Solar Cells

Energy Losses in Small‐Molecule Organic Photovoltaics

Study of the Contributions of Donor and Acceptor Photoexcitations to Open Circuit Voltage in Bulk Heterojunction Organic Solar Cells

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