High-performance Organic Solar Cells Research Articles

Molecular designing of four high performance pyrazine-based non-fullerene acceptor materials with naphthalene diimide-based small organic solar cells.

We design four high performance non-fullerene acceptor materials by applying strong electron withdrawing groups at the end of A-D-A-D-A type organic solar cells molecules and compute their different opto-electronic and photovoltaic properties, including absorption spectrum, electron density, solubility strength, charge mobilities for electrons and holes, stability of HOMO/LUMO energy orbitals, excitation energies required for charge transfer mechanisms, and morphology of device with the help of DFT approaches using the principles of quantum mechanics. The newly designed molecules showed strong absorption bands between 420 to 650nm, low HOMO energy values from -7.24 to -7.28eV, large % ETC from 35 to 65%, and small excitation energies from 2.28 to 2.47eV in the organic solvent chloroform; 410 to 620nm, 31 to 64%, and 2.42 to 2.56eV, respectively, in gas phase conditions. Solubility strengths of the newly designed molecules were also high, varying from 5.3039 to 18.4749 Debye in the ground and excited states. Power conversion efficiencies of the designed molecules are expected to be high because they show better results than the R molecule. Open circuit voltages of designed molecules range from 3.67 to 3.54V with respect to the PCBM. Reorganization energies for electron transport vary from 0.0153 to 0.0175eV and for hole transport from 0.0231 to 0.0254eV. This computational study proves that the newly designed molecules with non-fullerene acceptors are superior and thus are recommended for the future construction of high performance organic solar cells devices. Graphical Abstract Orbital's energy comparisons of four newly designed non-fullerene acceptor materials with naphthalene diimide-based small organic solar cells.

Isomerization of Perylene Diimide Based Acceptors Enabling High-Performance Nonfullerene Organic Solar Cells with Excellent Fill Factor.

A strategy that employs the central‐core regiochemistry to develop two isomeric perylene diimide (PDI)‐based small molecular acceptors (SMAs), BPT‐Se and BPT‐Se1, is introduced, and the effect of the central‐core regiochemistry on the optical, electronic, charge‐transport, photovoltaic, and morphological properties of the molecules and their devices is investigated. The PDBT‐T1:BPT‐Se1‐based device delivers a power conversion efficiency (PCE) of 9.54% with an excellent fill factor (FF) of 73.2%, while the BPT‐Se‐based device yields a PCE of 7.78%. The large improvement of PCE upon isomerization of BPT‐Se should be ascribed to the concurrent enhancement of FF, short circuit current ( J SC), and open circuit voltage (V OC) of the PDBT‐T1:BPT‐Se1 devices. The higher FF of the organic solar cells (OSCs) based on PDBT‐T1:BPT‐Se1 can be attributed to the higher charge dissociation and charge collection efficiency, less bimolecular combination, more balanced µ h/µ e, better molecular packing and a more favorable morphology. It is worth mentioning that the FF of 73.2% is the highest value for PDI‐based SMAs OSCs to date. The result shows that regiochemistry of the central core in PDI‐based SMAs greatly affects the physicochemical properties and photovoltaic performance. The success of the isomerization strategy offers exciting prospects for the molecular design of PDI‐based SMAs.

Highly Efficient Fullerene-Free Organic Solar Cells Operate at Near Zero Highest Occupied Molecular Orbital Offsets.

Herein, we investigated a series of fullerene-free organic solar cells (OSCs) based on six different donor:acceptor (D:A) blends with varied highest occupied molecular orbital (HOMO) offsets from -0.05 to 0.21 eV. First, to verify the energetic compatibility of a specific D:A pair, especially for HOMO offsets, we established a simple method to estimate the hole transfer tendencies between D and A by using bilayer hole-only devices. It reveals that the asymmetrical diode effect of the bilayer hole-only devices can correlate with the FF and Jsc of the relevant OSCs. Second, to find out whether HOMO offset is the main restriction of hole transfer, we measured transient absorption spectra and examined the hole transfer behavior in the blends, revealing that the occurrence of hole transfer is independent of the HOMO offsets and ultrafast in the time scale of ≤4.6 ps for those blends with ≥0 eV HOMO offsets. In contrast, a negative HOMO offset can significantly slow down the hole transfer with a half-time of ∼400 ps. Furthermore, we compare the device parameters under varied light intensities and discover that the bimolecular recombination should be one of the main restrictions for high device performance. Surprisingly, small HOMO offsets of 0 and 0.06 eV can also enable high PCEs of 10.42% and 11.75% for blend 2 (PTQ10:HC-PCIC) and blend 3 (PBDB-TF:HC-PCIC), respectively. Overall, our work demonstrates not only the validity of high-performance OSCs operating at the near zero HOMO offsets but also the charge dynamic insights of these blends, which will help gain understanding on the further improvement of OSCs.

Polymer Donors for High-Performance Non-Fullerene Organic Solar Cells.

Over the past few years, non-fullerene organic solar cells have been a focus of research and their power conversion efficiencies have been improved dramatically from about 6 % to over 14 %. In addition to innovations in non-fullerene acceptors, the ongoing development of polymer donors has contributed significantly to the rapid progress of non-fullerene organic solar cell performance. This Minireview highlights the polymer donors that enable high-performance non-fullerene organic solar cells. We show the impressive photovoltaic devices results achieved by some of important classes of conjugated polymer systems in non-fullerene organic solar cells. We discuss the molecular design strategies as far as developing matching polymer donors for non-fullerene acceptors. We conclude with a brief summary and outlook for advances in donor polymers required for commercialization.

Highly Efficient Benzo-Furan-Based Electron Acceptor Derived from One-Pot Synthesis for High-Performance Bulk Heterojunction Solar Cells

A new benzofuran-derived fulleropyrrolidine derivative denoted as FB-C60 is synthesized by Prato single step synthetic protocol and successfully utilized as an electron acceptor in the bulk heterojunction organic solar cells (OSCs). The molecule possesses significant optoelectronic and redox properties, which are compatible with popular polymer donors. The OSCs constructed from PTB7/FB-C60 blends yielded a highest power conversion efficiency (PCE) of 8.1%. The champion device that was fabricated from PTB7-Th/FB-C60 bulk-composite film demonstrated a PCE of 9.6%, open circuit voltage of 0.83 V, series resistance of 3.3 Ω·cm–2 and 75.1% of external quantum efficiency at 640 nm wavelength. A promising electron mobility of 1.2 × 10–3 cm2 V–1 s–1 of FB-C60 is observed in the fabricated device. FB-C60 shows the potential to positively replace the conventional PCBM to fabricate “cost-effective” high-performance OSCs.

Pairing 1D/2D-conjugation donors/acceptors towards high-performance organic solar cells

Pairing 1D/2D-conjugation donors/acceptors towards high-performance organic solar cells

Pairing 1D/2D-conjugation donors/acceptors towards high-performance organic solar cells

1D conjugated donor FTAZ, 2D conjugated donor J71, 1D conjugated acceptor ITIC1, and 2D conjugated acceptor ITIC2 were used to investigate the effects of conjugation dimension on the performance of organic solar cells.

Achieving high-performance non-halogenated nonfullerene acceptor-based organic solar cells with 13.7% efficiencyviaa synergistic strategy of an indacenodithieno[3,2-b]selenophene core unit and non-halogenated thiophene-based terminal group

The combination of indacenodithieno[3,2-b]selenophene core unit and thiophene-containing IC is a successful synergistic strategy with PCE of 13.7%, which is the highest value in NFAs with thiophene-containing IC for binary OSCs.

Multifunctional asymmetrical molecules for high-performance perovskite and organic solar cells

Asymmetrical n-type molecules are high-performance multifunctional materials simultaneously used as ETMs or ILMs in PVKSCs and electron acceptors in OSCs.

A universal layer-by-layer solution-processing approach for efficient non-fullerene organic solar cells

A universal layer-by-layer solution-processing approach is proven to be effective for the fabrication of high-performance non-fullerene organic solar cells.

Exquisite modulation of ZnO nanoparticle electron transporting layer for high-performance fullerene-free organic solar cell with inverted structure

An inverted organic solar cell with finely tuned ZnO : PFN-Br electron transporting layer shows 13.8% power conversion efficiency and 78.8% fill factor.

Asymmetric selenophene-based non-fullerene acceptors for high-performance organic solar cells

Two novel selenophene-containing building blocks have been developed as central cores to construct high-performance asymmetric non-fullerene acceptors (SePTT-2F and SePTTT-2F). Organic solar cells based on SePTTT-2F with more extended backbone conjugation delivered a high efficiency of 12.24% with an outstanding fill factor of 75.9%.

High-performance organic solar cells based on polymer donor/small molecule donor/nonfullerene acceptor ternary blends

Polymer donor/small molecule donor/nonfullerene acceptor ternary organic solar cells afford efficiency of 13.1%, higher than that of the polymer donor/nonfullerene acceptor binary blend (12.1%).

Solution-processable n-doped graphene-containing cathode interfacial materials for high-performance organic solar cells

Solution-processable n-doped graphene-containing cathode interfacial material with a low work function demonstrates 16.52% power conversion efficiency in organic solar cells.

Natural Dyes and Their Derivatives Integrated into Organic Solar Cells.

Natural photosynthetic systems contain several dyes such as carotenoids or chlorophylls which are adequately arranged to produce efficient photoinduced charge separation and electron transfer. Several research groups have attempted integrating these natural dyes and photosynthetic systems into functional organic solar cells (OSCs) producing power conversion efficiencies (PCEs) up to 0.99%. The studies presented in this short review emphasize that functionalization of natural dyes can considerably improve their PCEs. For instance, chlorophyll derivatives can yield PCEs up to 2.1%, and copolymers produced with isoindigo as an electron-deficient unit generate high PCEs up to 8%, respectively, when combined with fullerene C70 based electron acceptors in the OSC active layers. An alternative approach for natural dye integration into OSC architectures is to place these light-harvesting antennas at the interface between the active layer and the charge collection layers in these low-cost photovoltaic devices. This strategy produces large PCE increases up to 35% with respect to OSCs prepared without the interlayer. When light-harvesting systems are combined with silver nanoprisms as interlayers, additional localized surface plasmon resonance effects result in high-performance OSCs that integrate natural photosynthetic systems and demonstrate a PCE over the milestone value of 10%.

Self-Organized Large-Scale Integration of Mesoscale-Ordered Heterojunctions for Process-Intensified Photovoltaics

Self-organization of large-area micro- or nanoscale patterns, using an inexpensive one-step process, is proposed for the fabrication of low-cost, high-performance organic solar cells. The authors employ spin dewetting of a conductive polymer to fabricate an array of micro- to nanoscale ordered heterojunctions, and demonstrate improvements in the key performance indicators of the resulting organic photovoltaic devices. A theoretical study with appropriate boundary conditions is carried out to understand the pattern formation, and simulations are performed to probe the effects of varying active-layer geometry on device characteristics.

Design and application of volatilizable solid additives in non-fullerene organic solar cells

Most of the high-performance organic solar cells are fabricated with the assistance of high-boiling-point solvent additives to optimize their charge transport properties; this has adverse effects on the OSCs’ stability and reproducibility in large-scale production. Here, we design volatilizable solid additives by considering the molecular structure feature of an acceptor–donor–acceptor-type non-fullerene acceptor. The application of solid additives can enhance the intermolecular π–π stacking of the non-fullerene acceptor and thus facilitate the charge transport properties in the active layers, leading to improved efficiencies of OSCs. Importantly, devices fabricated using volatilizable solid additives exhibit higher stability and reproducibility when compared with the OSCs processed with solvent additives. Our results not only demonstrate an approach of applying volatilizable solid additives to benefit the large-scale production of OSCs but also provide a potential direction for designing specific solid additives for different active layers.

Near-infrared non-fullerene acceptors based on dithienyl[1,2-b:4,5-b’]benzodithiophene core for high performance PTB7-Th-based polymer solar cells

Two non-fullerene electron acceptors (BT-SFIC and BT-FIC) bearing a dithienyl[1,2-b:4,5-b’]benzodithiophene core were designed and synthesized. Due to the strong electron-withdrawing ability of fluorine atoms, these two non-fullerene acceptors both show near-infrared absorption around 900 nm, with a narrow bandgap of 1.44 and 1.39 eV for BT-SFIC and BT-FIC, respectively. BT-SFIC and BT-FIC have complementary absorption and matched energy level with PTB7-Th. PSCs based on PTB7-Th donor and these two acceptors both show good charge dissociation and collection, small charge recombination and good active layer morphology. However, BT-FIC bearing much more fluorine have much higher electron mobility. And the PSCs based on PTB7-Th: BT-FIC gives a maximum PCE of 10.10% with a VOC of 0.73 eV, a JSC of 21.28 mA cm−2 and an FF of 65%, which is among in the high-performance polymer organic solar cells based on PTB7-Th.

Nanoscale Insight into Performance Loss Mechanisms in P3HT:ZnO Nanorod Solar Cells

Hybrid solar cells based on semiconducting polymers and metal oxides offer the possibility of combining the best attributes of both constituents to achieve efficient and low-cost solar energy harvesting. Active layers consisting of ZnO nanorods and semiconducting polymer poly(3-hexylthiophene), P3HT, have been studied extensively over the past decade. This type of solar cell, however, still exhibits a relatively low performance and poor device-to-device reproducibility. For insight into the performance bottlenecks in P3HT:ZnO nanorod solar cells, we employ a point-by-point current–voltage mapping method using conductive atomic force microscopy to probe the local photovoltaic properties of hybrid P3HT:ZnO nanorod active layers with nanoscale spatial resolution. We observe that the short-circuit current density, open-circuit voltage, fill factor, and power conversion efficiency are highly heterogeneous and sensitive to the local thickness of the P3HT hole transport layer that sits atop the active layer, with local power conversion efficiencies reaching as high as double those seen in macroscopic devices. We further demonstrate that this hybrid system exhibits a high charge photogeneration rate, which approaches that in high-performance organic solar cells; however, photocurrent is limited by a low charge collection probability under short-circuit conditions. These experiments suggest the potential for significant performance gains in hybrid organic–inorganic nanorod solar cells through improvements in active layer uniformity and charge extraction efficiency.

Functionalized Graphene Oxide Enables a High-Performance Bulk Heterojunction Organic Solar Cell with a Thick Active Layer.

Novel functionalized graphene oxide π-π stacking with conjugated polymers (P-GO) is fabricated via a simple ethanol-mediated mixing method, leading to better dispersion in organic nonpolar solvents and bypassing the inherent restrictions of hydrophilicity and oleophobicity. We analyze the mechanism of the incorporation of P-GO into inverted organic solar cells (OSCs) based on a poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4- b]thiophenediyl]] (PTB7):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) system to investigate the possibility of high-performance thick-film OSC fabrication. It is verified that the incorporation of P-GO into the PTB7:PC71BM blend films leads to a decreased π-π stacking distance, enlarged coherence length for polymer, and optimized phase separation, resulting in more effective charge dissociation, reduced bimolecular recombination, and more balanced charge transport. The OSCs with 1% P-GO incorporation demonstrate a thickness-insensitive fill factor (57.8%) and power conversion efficiency (PCE) (7.31%) even with 250 nm thick photoactive layers, leading to a dramatic PCE enhancement of 34% compared with the control devices with the same thickness.