Single-Junction Organic Solar Cell with over 15% Efficiency Using Fused-Ring Acceptor with Electron-Deficient Core

18% Efficiency organic solar cells

Non-fullerene acceptors (NFAs) are currently a major focus of research in the development of bulk-heterojunction organic solar cells (OSCs). In contrast to the widely used fullerene acceptors (FAs), the optical properties and electronic energy levels of NFAs can be readily tuned. NFA-based OSCs can also achieve greater thermal stability and photochemical stability, as well as longer device lifetimes, than their FA-based counterparts. Historically, the performance of NFA OSCs has lagged behind that of fullerene devices. However, recent developments have led to a rapid increase in power conversion efficiencies for NFA OSCs, with values now exceeding 13%, demonstrating the viability of using NFAs to replace FAs in next-generation high-performance OSCs. This Review discusses the important work that has led to this remarkable progress, focusing on the two most promising NFA classes to date: rylene diimide-based materials and materials based on fused aromatic cores with strong electron-accepting end groups. The key structure–property relationships, donor–acceptor matching criteria and aspects of device physics are discussed. Finally, we consider the remaining challenges and promising future directions for the NFA OSCs field. Non-fullerene acceptors have been widely used in organic solar cells over the past 3 years. This Review focuses on the two most promising classes of non-fullerene acceptors — rylene diimide-based materials and fused-ring electron acceptors — and discusses structure–property relationships, donor– acceptor matching criteria and device physics, as well as future research directions for the field.

Non-fullerene acceptors for organic solar cells

Over the past three years, a particularly exciting and active area of research within the field of organic photovoltaics has been the use of non-fullerene acceptors (NFAs). Compared with fullerene acceptors, NFAs possess significant advantages including tunability of bandgaps, energy levels, planarity and crystallinity. To date, NFA solar cells have not only achieved impressive power conversion efficiencies of ~13–14%, but have also shown excellent stability compared with traditional fullerene acceptor solar cells. This Review highlights recent progress on single-junction and tandem NFA solar cells and research directions to achieve even higher efficiencies of 15–20% using NFA-based organic photovoltaics are also proposed.

Next-generation organic photovoltaics based on non-fullerene acceptors

The bulk-heterojunction blend of an electron donor and an electron acceptor material is the key component in a solution-processed organic photovoltaic device. In the past decades, a p-type conjugated polymer and an n-type fullerene derivative have been the most commonly used electron donor and electron acceptor, respectively. While most advances of the device performance come from the design of new polymer donors, fullerene derivatives have almost been exclusively used as electron acceptors in organic photovoltaics. Recently, nonfullerene acceptor materials, particularly small molecules and oligomers, have emerged as a promising alternative to replace fullerene derivatives. Compared to fullerenes, these new acceptors are generally synthesized from diversified, low-cost routes based on building block materials with extraordinary chemical, thermal, and photostability. The facile functionalization of these molecules affords excellent tunability to their optoelectronic and electrochemical properties. Within t...

Nonfullerene Acceptor Molecules for Bulk Heterojunction Organic Solar Cells

Recent Advances in Bulk Heterojunction Polymer Solar Cells

A cluster type of electron acceptor, TPB, bearing four α-perylenediimides (PDIs), was developed, in which the four PDIs form a cross-like molecular conformation while still partially conjugated with the BDT-Th core. The blend TPB:PTB7-Th films show favorable morphology and efficient charge dissociation. The inverted solar cells exhibited the highest PCE of 8.47% with the extraordinarily high Jsc values (>18 mA/cm2), comparable with those of the corresponding PC71BM/PTB7-Th-based solar cells.

Covalently Bound Clusters of Alpha-Substituted PDI—Rival Electron Acceptors to Fullerene for Organic Solar Cells

This paper describes the synthesis of low bandgap copolymers incorporating an artificial sweetener derivative, N-alkyl, 3-oxothieno[3,4-d]isothiazole 1,1-dioxide (TID) This new TID unit is identical to the well-known thieno[3,4-c]pyrrole-4,6-dione (TPD) unit except that one carbonyl has been replaced by a sulfonyl group Semi-empirical calculations on the local dipole moment change between ground and excited states (Δμge) in the repeating units of the new polymer indicate that the replacement of the carbonyl by a sulfonyl group leads to larger Δμge values The resulting polymers exhibit a diminished power-conversion efficiency (PCE) compared to a bulk heterojunction (BHJ) solar cells with PC71BM as an acceptor, which extends the correlation between PCE and Δμge of single repeating units in p-type polymers to a new regime Detailed studies show that the strongly electron-withdrawing sulfonyl group is detrimental to charge separation in alternating copolymers containing a TID unit

Tuning the Polarizability in Donor Polymers with a Thiophenesaccharin Unit for Organic Photovoltaic Applications

We report the properties of a new series of wide band gap photovoltaic polymers based on the N-alkyl 2-pyridone dithiophene (PDT) unit. These polymers are effective bulk heterojunction solar cell materials when blended with phenyl-C71-butyric acid methyl ester (PC71BM). They achieve power conversion efficiencies (up to 5.33%) high for polymers having such large bandgaps, ca. 2.0 eV (optical) and 2.5 eV (electrochemical). Grazing incidence wide-angle X-ray scattering (GIWAXS) reveals strong correlations between π–π stacking distance and regularity, polymer backbone planarity, optical absorption maximum energy, and photovoltaic efficiency.

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Wide bandgap OPV polymers based on pyridinonedithiophene unit with efficiency >5%

The development of functional polymers is a very active research field that covers every aspects of our lives and has had huge impact on human society due to their applications in many cutting-edge technologies, such as energy conversion and storage, electronic devices, biotechnology, and health care, to name a few [1]. Scientists from different disciplines have invented numerous new materials for those purposes. Integral to these efforts is the development of efficient, versatile, and scalable synthesis techniques, which in turn enable the development of new functional materials. Thus, new synthetic methodologies are always a critical research topic that is actively pursued. A large number of recent advances can be cited to support this view, such as ring-opening metathesis polymerization (ROMP), atom transfer radical polymerization (ATRP, a type of “living” radical polymerization), and controlled Ziegler–Natta polymerization [2, 3]. Most recently, polycondensations based on transition metal-catalyzed CC bond formation reactions have emerged as important methodologies for synthesis of electro-optic materials containing large systems. These reactions include Stille, Suzuki, Negishi, Heck, and so on [4–7]. The Stille reaction is one of the best methods for the synthesis of organic functional materials due to its excellent compatibility with various functional groups and high reaction yield. The most attractive application of the Stille coupling reaction is in the synthesis of conjugated, polyaromatic semiconducting materials, which are an important class of materials for organic electronics. These materials exhibit good solubility in various solvents, which allows them to be fabricated into devices using inexpensive solution-phase printing techniques [8]. Over the past several decades, the development of semiconducting polymers has led to the advent of new technologies for numerous applications, ranging from organic light-emitting diodes (OLEDs), field effect transistor (FET), and organic photovoltaic (OPV) solar cells [7]. Among these semiconducting polymers, the majority of them, especially those containing thiophenemoieties, can be synthesized via Stille polycondensation from-related monomers. These polymers bear a wide variety of functional groups and their emergence is enabled by the power and broad scope of the

Alexander M. Schneider

Papers

Recent Advances in Bulk Heterojunction Polymer Solar Cells

Covalently Bound Clusters of Alpha-Substituted PDI—Rival Electron Acceptors to Fullerene for Organic Solar Cells

Tuning the Polarizability in Donor Polymers with a Thiophenesaccharin Unit for Organic Photovoltaic Applications

Wide bandgap OPV polymers based on pyridinonedithiophene unit with efficiency >5%

Stille Polycondensation: A Versatile Synthetic Approach to Functional Polymers