Nanoscale composite of detonation nanodiamond (DND) and polypyrrole (PPy) as a representative of organic light-harvesting polymers is explored for energy generation, using nanodiamond as an inorganic electron acceptor. We present a technology for the composite layer-by-layer synthesis that is suitable for solar cell fabrication. The formation, pronounced material interaction, and photovoltaic properties of DND-PPy composites are characterized down to nanoscale by atomic force microscopy, infrared spectroscopy, Kelvin probe, and electronic transport measurements. The data show that DNDs with different surface terminations (hydrogenated, oxidized, poly-functional) assemble PPy oligomers in different ways. This leads to composites with different optoelectronic properties. Tight material interaction results in significantly enhanced photovoltage and broadband (1–3.5 eV) optical absorption in DND/PPy composites compared to pristine materials. Combination of both oxygen and hydrogen functional groups on the nanodiamond surface appears to be the most favorable for the optoelectronic effects. Theoretical DFT calculations corroborate the experimental data. Test solar cells demonstrate the functionality of the concept.

Interaction of diamond with molecules is important for various applications. For instance, experimentally observed charge transfer between bulk diamond and polypyrrole (PPy) is promising for photovoltaics. Here we explore the interactions of PPy with surfaces of nanodiamonds (NDs) by density functional theory (DFT) calculations at the B3LYP/6-31G(d) level of theory. The most probable H-terminated 1 Â 1 (111) and 2 Â 1 (100) diamond surface facets are considered. Geometrical arrangement, binding energy (E b ), interaction energy (E int ), charge transfer (Dq), and HOMO-LUMO gap are calculated on geometrically relaxed structures of PPy on the ND facets in physisorbed or chemisorbed configuration. Energetically, the most favorable is physisorption of PPy on NDs. For chemisorption, one-bond contact is more favorable than two-bond contact, with the most probable binding on (100) facet. Charge transfer of electrons (up to Dq ¼ À0.11 e À ) from PPy to diamond is observed for all the configurations in the dark. In some cases, the calculations reveal spatial separation of the HOMO and LUMO, which may be useful for photovoltaic applications. Truncated octahedral ND (left), (111) facets are in blue, (100) facets are in red. (111)-(100)-(111) corner of ND (bottom), and (111) facet with chemisorbed PPy (top). C atoms are in gray, H atoms are in white, N atoms are in blue.

Spatial separation and variable energy gap between the HOMO and LUMO at the polypyrrole–nanodiamond interface were calculated by DFT.