18.73% efficient and stable inverted organic photovoltaics featuring a hybrid hole-extraction layer.

Developing efficient and stable organic photovoltaics (OPVs) is crucial for the technology's commercial success. However, combining these key attributes remains challenging. Herein, we incorporate the small molecule 2-((3,6-dibromo-9H-carbazol-9-yl)ethyl)phosphonic acid (Br-2PACz) between the bulk-heterojunction (BHJ) and a 7 nm-thin layer of MoO3 in inverted OPVs, and study its effects on the cell performance. We find that the Br-2PACz/MoO3 hole-extraction layer (HEL) boosts the cell's power conversion efficiency (PCE) from 17.36% to 18.73% (uncertified), making them the most efficient inverted OPVs to date. The factors responsible for this improvement include enhanced charge transport, reduced carrier recombination, and favourable vertical phase separation of donor and acceptor components in the BHJ. The Br-2PACz/MoO3-based OPVs exhibit higher operational stability under continuous illumination and thermal annealing (80 °C). The T80 lifetime of OPVs featuring Br-2PACz/MoO3 - taken as the time over which the cell's PCE reduces to 80% of its initial value - increases compared to MoO3-only cells from 297 to 615 h upon illumination and from 731 to 1064 h upon continuous heating. Elemental analysis of the BHJs reveals the enhanced stability to originate from the partially suppressed diffusion of Mo ions into the BHJ and the favourable distribution of the donor and acceptor components induced by the Br-2PACz.

Stacks of graphene with silicane or germanane: a first-principles study.

We report the results of density-functional theory calculations on the stability and properties of hybrid layered systems composed of graphene and silicane or germanane monolayers. We find that the interlayer binding energy between the sheets is comparable to that of graphite, indicating that the creation of the corresponding stacks is feasible. Moreover, we show that the hybrid systems are stable against the formation of defects caused by the transfer of hydrogen atoms from one layer to another. Finally, we find that the graphene layer of the graphene-germanane stack retains its pristine electronic properties, at least close to the Fermi level. Therefore, stacks of graphene with silicane or germanane may be utilized in graphene-based devices by combining zero-gap graphene with wide band-gap two-dimensional semiconductors.