ConspectusEfficient photovoltaics (PV) require capturing and converting solar energy across a broad range of energy. Losses due to thermalization and sub-bandgap photons place, however, significant boundaries on the performance of solar cells. For conventional single-junction cells, the theoretical maximum power conversion efficiency is capped at 33%, a constraint known as the detailed balance limit. Realizing the full potential of PVs requires developing novel strategies to overcome this fundamental obstacle. This Account describes the photon-management capabilities of acenes and addresses these fundamental losses en-route toward enhancing PV performances.For high-energy photons that exceed the semiconductor's bandgap energy, singlet fission (SF) is a down-conversion pathway to mitigate thermalization losses. SF is a process in organic materials, in which a singlet excited state is split into two independent triplet excited states, effectively doubling the number of charge carriers. Pentacenes stand out among acenes due to their exergonic nature of SF. Numerous molecular pentacene dimers have been synthesized to elucidate the relationship between structure and enhancing SF efficiency.A broader light-harvesting range of SF materials is realized by covalently attaching complementary absorbing energy donors to set up energy donor–acceptor conjugates. Förster resonance energy transfer (FRET) is operative in these energy donor-acceptor conjugates, effectively extending the absorption of SF materials, as the energy donor efficiently transfers its absorbed excitation energy to the energy acceptor. Our studies on various binding motifs show that FRET efficiency depends not only on parameters like the energy donor–acceptor distance and spectral overlap but also on subtle factors such as the alignment of transition dipoles, which significantly affect the energy transfer dynamics and efficiency.Turning to low-energy photons, triplet–triplet annihilation up-conversion (TTA-UC) provides a means of light up-conversion and, thereby, the reduction of sub-bandgap losses. In TTA-UC, a singlet excited state that is potent enough to generate charge carriers is formed by combining two triplet excitons. It is effectively the reverse process of SF. The higher triplet energy of tetracene and an endergonic SF renders them highly effective for TTA-UC. We focus on various tetracene-based systems that maximize TTA-UC efficiency.Besides TTA-UC, two-photon absorption (TPA) is yet another mechanism to leverage below-bandgap photons. It is a nonlinear optical (NLO) process, and acenes reveal NLO properties that are essential for extending light absorption into the near-infrared and still powering SF. We demonstrate in our proof-of-concept studies how TPA further broadens the application potential of acenes for PV systems.The strategies outlined in this Account illustrate that acenes are valuable for addressing mechanistic losses in conventional solar cells. In the final section, we examine light storage following SF by means of interfacial electron transfer. Efficient charge-injection powered by SF materials still requires more research before being implemented in large-scale PV designs.Overall, the advances discussed in this Account not only highlight the pivotal role of acenes as model systems to investigate photon down- and up-conversion processes but also paint a promising picture that more efficient solar energy conversion schemes exceeding the detailed-balance limit can be realized by implementing these materials.

Phillip M. Greißel

Anna-Sophie Wollny

Yifan Bo

Dominik Thiel

Category	Quartile
材料科学	1
材料科学, 化学综合	1
材料科学, 材料科学综合	1

Molecular Acenes for Light Capture, Conversion, and Storage

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Journal Info

Category	Quartile
MATERIALS SCIENCE, MULTIDISCIPLINARY	1