Role of HF in Oxygen Removal from Carbon Nanotubes: Implications for High Performance Carbon Electronics

Oxygen removal from SWNTs is crucial for many carbon electronic devices. This work shows that HF treatment followed by current stimulation is a very effective method for oxygen removal. Using a procedure involving HF treatment, current stimulation and spin-casting AgNWs onto a SWNT thin film, record high efficiency SWNT/<i>p</i>-Si solar cells have been developed

Coevaporated Bisquaraine Inverted Solar Cells: Enhancement Due to Energy Transfer and Open Circuit Voltage Control

There is currently enormous interest in the development of small molecule organic solar cells (SMSC), as in principle, these systems offer advantages over both conventional Si photovoltaics and organic polymer solar cells. Here, we report Förster Resonance Energy Transfer (FRET) enhanced inverted SMSC fabricated by coevaporating two different squaraine donors, a symmetrical squaraine (SQ, 2,4-bis-4-[(<i>N</i>,<i>N</i>-diisobutylamino)-2,6-dihydroxyphenyl] squaraine), and an asymmetrical squaraine (ASSQ, 2,4-bis-[(<i>N</i>,<i>N</i>-diisobutylamino)-2,6-dihydroxyphenyl]-4-(4-diphenyliminio) squaraine). ASSQ absorbs blue light (λ_max 540 nm) and emits from 550 nm to the near-infrared region, which overlaps with SQ absorption (λ_max 690 nm). Therefore, by utilizing a thin film containing the two squaraine donors as the active layer in a SMSC, we can both broaden the photovoltaic absorption spectrum, and reduce recombination loss as a result of FRET. This strategy has resulted in SMSC with power conversion efficiencies (PCE) which are up to 46% greater than those obtained by using a single squaraine donor. Ultrafast time-resolved photoluminescence and transient absorption spectroscopy provide clear evidence of FRET between the small molecules, with a rapid energy transfer time of ∼1 ps. At optimal blending, which correlates to the highest PCE measured, the efficiency of energy transfer is as high as 85%. Furthermore, in the devices containing two different squaraine molecules, the open circuit voltage (<i>V</i>_OC) is proportional to the fraction of the two donors in the blend, allowing us to predict the <i>V</i>_OC as the ratio of the two donors is changed. SMSC with inverted structures also demonstrate long-term stability in ambient conditions compared to devices employing a conventional architecture

Controlled Doping of Carbon Nanotubes with Metallocenes for Application in Hybrid Carbon Nanotube/Si Solar Cells

There is considerable interest in the controlled p-type and n-type doping of carbon nanotubes (CNT) for use in a range of important electronics applications, including the development of hybrid CNT/silicon (Si) photovoltaic devices. Here, we demonstrate that easy to handle metallocenes and related complexes can be used to both p-type and n-type dope single-walled carbon nanotube (SWNT) thin films, using a simple spin coating process. We report n-SWNT/p-Si photovoltaic devices that are >450 times more efficient than the best solar cells of this type currently reported and show that the performance of both our n-SWNT/p-Si and p-SWNT/n-Si devices is related to the doping level of the SWNT. Furthermore, we establish that the electronic structure of the metallocene or related molecule can be correlated to the doping level of the SWNT, which may provide the foundation for controlled doping of SWNT thin films in the future