Themed collection Special issue in honour of Kees Hummelen

In this perspective Kees Hummelen's contributions to fullerene research in our group at Santa Barbara, as well as Kees’ enormous contributions to organic electronics, will be presented as a set of “vignettes”.

Guest editors Hennie Valkenier, Dirk Vanderzande, Andries Meijerink and Maurizio Prato introduce this Journal of Materials Chemistry C issue in honour of Professor Kees Hummelen on the occasion of his retirement.

Methanofullerene [6,6]-phenyl C61-butyric acid methyl ester and its derivatives have been the workhorse acceptors in organic bulk heterojunction solar cells for more than two decades. Here, an overview of their charge transport properties is given.

This Perspective discusses the developments, opportunities, and challenges in the context of the use of alkyne-based organic semiconductors in photovoltaic devices.

This review highlights the important role of fullerene derivatives in several emerging research directions beyond OPV and summarizes recent progresses in the development of fullerene derivatives to boost device performance in these new fields.

This review summarizes recent advances in developing high-efficiency upconversion nanoparticles and nanomaterials for photovoltaic application.

Monitoring CO₂ levels in the atmosphere as well as in work place environments is strictly regulated.

Diketopyrrolopyrroles stand out due to their chemical and optoelectronic properties. Diketopyrrolopyrrole-single molecules applied in organic, dye-sensitized and perovskite solar cells are presented to give clues for future molecular optimizations.

Control of conductance through a single molecule via alternating anchoring points provides a unique perspective to design single-molecule electronic devices.

Two wide-bandgap copolymer donors with reduced synthesis cost offered decent PCEs up to 15.25% in organic solar cells.

To assess if salt-doping leaves anions and cations in the film, limiting the conductivity, one can apply a bias voltage and monitor the conductivity over time. If the doping is limited by unwanted ions, then the conductivity will increase with time.

Two benzothiadiazole derivatives annulated with 2-(1,3-dithiol-2-ylidene)malonitrile in the 4,5-position were prepared by a one-step procedure, and investigated as end-groups in non-fullerene acceptors for indoor photovoltaic applications.

First-time spectroscopic and computational investigations to elucidate the role of a dicationic salt in the optical, electrical and electronic properties of a triarylamine hole transport material, SFX-MeOTAD.

The sensitization of lanthanide-doped upconversion nanocrystals (UCNCs) using organic dyes with a broad and intense optical absorption is an interesting approach for efficient excitation-energy harvesting and enhancing the upconversion luminescence.

Experimentally established, non-equilibrium temperature/composition phase diagrams are demonstrated to be useful beyond rationalization of optimum OPV blend composition but also as tools for rapid, qualitative structure–property mapping.

Here, we explore the potential of subphthalocyanines (SubPcs) as ETMs in PSCs, where the perovskite is deposited by either solution processing or thermal evaporation. A maximum PCE of 10.8% was achieved with the champion device.

The synergistic use of X-ray scattering and molecular dynamics simulations reveals the structure–property relationships of [60]fullerene derivatives with oligoethylene–glycol side chains.

Polyoxometalate-bis-pyrene receptors for phenyl-C61-butyric acid methyl ester (PCBM) provide an interfacial layer (IFL) material enhancing the open circuit voltage of the organic photovoltaic device of about 34% under applied bias of ±5 V.

We report on the synthesis and single-molecule conductance of a para-oligo(phenylene)ethynylene derivative with a non-symmetric positioned internal anchor group that gives rise to three conduction pathways of well distinctive conductance and length.

We report the design of a synthetically easy accessible axial chirality-inducing framework for an achiral chromophore of choice. The spatial arrangement excitonically couples the chromophores and thus results in intense molar dichroism.

A new aromatic ladder polymer with a polyacene skeleton shows an unexpectedly high flexibility of its double-stranded backbone.

Two thiophene-based macrocycles have been synthesised and their optoelectronics applications have been investigated.

A new non-fullerene small molecule (MPU6) containing thienylethynylselenophene bridges, has been studied as an acceptor along with PC₇₁BM and TDTBTA as a donor in ternary solution-processed bulk heterojunction polymer solar cells, showing a PCE of 15.60%.

Twofold effect of molecular functionalization of defective transition metal dichalcogenides (TMDCs).

The effects of alkyl side units in double-cable conjugated polymers on the photovoltaic performance of single-component organic solar cells were systematically studied.