Ben

Organic photovoltaics (OPVs) demostrate certified cell efficiencies of over 17% and are expected to contribute to versatile applications powered by solar energy. By taking into consideration different critical and “soft” key performance indicators, this work demonstrates material strategies to accelerate the development of OPV technology toward a GW era.

Abstract

With the rise of the solar power century, photovoltaic applications and installations will go beyond the traditional green field power plants and enter any aspect of daily life. Organic photovoltaics (OPVs) demonstrate certified cell efficiencies of over 17% and are expected to contribute to versatile applications powered by solar energy, for instance, applications rely on flexibility, transparency, color management, or integrability. In this work, the progress of OPV technology is briefly reviewed and the material strategies to accelerate OPV technology toward a GW era are analyzed. In addition to the exciting efficiency values achieved for small area devices, there are many important criteria deciding the success of OPV technology. By taking into consideration the synthetic complexity of OPV materials and the operational stability of OPV devices, the industrial figure of merit (i‐FoM) is proposed as a fast and reliable method to verify the true potential of a novel material. Furthermore, “soft” key performance indicators are introduced, such as toxicity, flexibility, transparency, processing, which require different development strategies to reflect the potential of OPV technology for specific applications.

Publication date: 18 November 2020

Source: Joule, Volume 4, Issue 11

Author(s): Xixiang Zhu, Guichuan Zhang, Jia Zhang, Hin-Lap Yip, Bin Hu

An aqueous‐solution‐processed cathode interlayer based on cost‐effective organosilica nanodots (OSiNDs) is demonstrated for organic solar cells (OSCs) with power conversion efficiency over 17% and excellent operational stability. The high photostability of OSiNDs‐based OSCs is attributed to the avoidance of photoinduced shunts and the photocatalytic effect, which are ineluctable shortcomings in inverted OSCs based on ZnO cathode interlayers.

Abstract

The performance and industrial viability of organic photovoltaics are strongly influenced by the functionality and stability of interface layers. Many of the interface materials most commonly used in the lab are limited in their operational stability or their materials cost and are frequently not transferred toward large‐scale production and industrial applications. In this work, an advanced aqueous‐solution‐processed cathode interface layer is demonstrated based on cost‐effective organosilica nanodots (OSiNDs) synthesized via a simple one‐step hydrothermal reaction. Compared to the interface layers optimized for inverted organic solar cells (i‐OSCs), the OSiNDs cathode interlayer shows improved charge carrier extraction and excellent operational stability for various model photoactive systems, achieving a remarkably high power conversion efficiency up to 17.15%. More importantly, the OSiNDs’ interlayer is extremely stable under thermal stress or photoillumination (UV and AM 1.5G) and undergoes no photochemical reaction with the photoactive materials used. As a result, the operational stability of inverted OSCs under continuous 1 sun illumination (AM 1.5G, 100 mW cm⁻²) is significantly improved by replacing the commonly used ZnO interlayer with OSiND‐based interfaces.

Publication date: 19 August 2020

Source: Joule, Volume 4, Issue 8

Author(s): Lingeswaran Arunagiri, Zhengxing Peng, Xinhui Zou, Han Yu, Guangye Zhang, Zhen Wang, Joshua Yuk Lin Lai, Jianquan Zhang, Yan Zheng, Chaohua Cui, Fei Huang, Yingping Zou, Kam Sing Wong, Philip C.Y. Chow, Harald Ade, He Yan

Solid‐state ¹⁹F magic angle spinning nuclear magnetic microscopy and elemental mapping are introduced to probe the structures of ternary and quaternary blends. The presence of the individual guest paths minimizes the influence on charge generation and transport of the host system, allowing cooperation of the parallel‐like subcells, producing impressive 17.2% efficiency via a quaternary strategy.

Abstract

Ternary strategies show over 16% efficiencies with increased current/voltage owing to complementary absorption/aligned energy level contributions. However, poor understanding of how the guest components tune the active layer structures still makes rational selection of material systems challenging. In this study, two phthalimide based ultrawide bandgap polymer donor guests are synthesized. Parallel energies between the highest occupied molecular orbitals of host and guest polymers are achieved via incorporating selnophene on the guest polymer. Solid‐state ¹⁹F magic angle spinning nuclear magnetic spectroscopy, graze‐incidence wide‐angle X‐ray diffraction, elemental transmission electron microscopy mapping, and transient absorption spectroscopy are combined to characterize the active layer structures. Formation of the individual guest phases selectively improves the structural order of donor and acceptor phase. The increased electron mobility in combination with the presence of the additional paths made by the guest not only minimizes the influence on charge generation and transport of the host system but also contributes to increasing the overall current generation. Therefore, phthalimide based polymers can be potential candidates that enable the simultaneous increase of open‐circuit voltage and short‐circuit current‐density via fine‐tuning energy levels and the formation of additional paths for enhancing current generation in parallel‐like multicomponent organic solar cells.

The influence of solvent additives on operation‐induced changes of the morphology in the active layer of organic solar cells is studied in operando. High boiling point solvent additives introduce an interpenetrating network of donor and acceptor in the films and change the device degradation mechanism from a short‐circuit current dominated one to a open‐circuit voltage dominated degradation.

Abstract

Solvent additives are known to modify the morphology of bulk heterojunction active layers to achieve high efficiency organic solar cells. However, the knowledge about the influence of solvent additives on the morphology degradation is limited. Hence, in operando grazing‐incidence small and wide angle X‐ray scattering (GISAXS and GIWAXS) measurements are applied on a series of PffBT4T‐2OD:PC₇₁BM‐based solar cells prepared without and with solvent additives. The solar cells fabricated without a solvent additive, with 1,8‐diiodoctane (DIO), and with o‐chlorobenzaldehyde (CBA) additive show differences in the device degradation and changes in the morphology and crystallinity of the active layers. The mesoscale morphology changes are correlated with the decay of the short‐circuit current J _sc and the evolution of crystalline grain sizes is codependent with the decay of open‐circuit voltage V _oc. Without additive, the loss in J _sc dominates the degradation, whereas with solvent additive (DIO and CBA) the loss in V _oc rules the degradation. CBA addition increases the overall device stability as compared to DIO or absence of additive.

Porphyrin is a very promising unit to construct low‐bandgap materials to harness solar photons in the near‐infrared region. This can help organic solar cells (OSCs) maximize solar energy utilization. Recent progress of porphyrin‐based materials, design and synthesis routes, morphology, and applications in OSCs is summarized, and future perspective and endeavors are discussed to facilitate higher performance for OSCs.

Abstract

With developments in materials, thin‐film processing, fine‐tuning of morphology, and optimization of device fabrication, the performance of organic solar cells (OSCs) has improved markedly in recent years. Designing low‐bandgap materials has been a focus in order to maximize solar energy conversion. However, there are only a few successful low‐bandgap donor materials developed with near‐infrared (NIR) absorption that are well matched to the existing efficient acceptors. Porphyrin has shown great potential as a useful building block for constructing low‐bandgap donor materials due to its large conjugated plane and strong absorption. Porphyrin‐based donor materials have been shown to contribute to many record‐high device efficiencies in small molecule, tandem, ternary, flexible, and OSC/perovskite hybrid solar cells. Specifically, non‐fullerene small‐molecule solar cells have recently shown a high power conversion efficiency of 12% using low‐bandgap porphyrin. All these have validated the great potential of porphyrin derivatives as effective donor materials and made DPPEZnP‐TRs a family of best low‐bandgap donor materials in the OSC field so far. Here, recent progress in the rational design, morphology, dynamics, and multi‐functional applications starting from 2015 will be highlighted to deepen understanding of the structure–property relationship. Finally, some future directions of porphyrin‐based OSCs are presented.