Single-walled carbon nanotubes (SWCNTs) have highly desirable attributes for solution-processable thin-film photovoltaics (TFPVs), such as broadband absorption, high carrier mobility, and environmental stability. However, previous TFPVs incorporating photoactive SWCNTs have utilized architectures that have limited current, voltage, and ultimately power conversion efficiency (PCE). Here, we report a solar cell geometry that maximizes photocurrent using polychiral SWCNTs while retaining high photovoltage, leading to record-high efficiency SWCNT-fullerene solar cells with average NREL certified and champion PCEs of 2.5% and 3.1%, respectively. Moreover, these cells show significant absorption in the near-infrared portion of the solar spectrum that is currently inaccessible by many leading TFPV technologies.

Formic acid (HCOOH) deprotonates on the open surfaces of Cu(110) and Cu(100) when exposed at 300 K. However, this does not occur on the close-packed surface of clean Cu(111). In this study, we show that the deprotonation of formic acid on atomically flat Cu(111) surfaces can be induced by pre-adsorbing polymeric formic acid clusters at low temperatures, and then annealing the system to break the acidic O-H bond of HCOOH adsorbed on the edges of the polymeric clusters. The thermal activation of HCOOH to bidentate formate was studied using a combination of infrared reflection absorption spectroscopy, scanning tunneling microscopy, X-ray photoelectron spectroscopy, and near edge X-ray absorption fine structure spectroscopy. Extended 1D formate structures self-assemble due to a templating effect introduced by the formation of long α-polymeric formic acid chains commensurate with the substrate.

Semiconducting single-walled carbon nanotube/fullerene bulk heterojunctions exhibit unique optoelectronic properties highly suitable for flexible, efficient, and robust photovoltaics and photodetectors. We investigate charge-transfer dynamics in inverted devices featuring a polyethylenimine-coated ZnO nanowire array infiltrated with these blends and find that trap-assisted recombination dominates transport within the blend and at the active layer/nanowire interface. We find that electrode modifiers suppress this recombination, leading to high performance.

For example, by systematically varying the thickness of the photoactive region (a tedious process), optical cavity modes that serve to enhance absorption can be tuned in frequency. [ 16 ] Furthermore, as we show here, optical transfer matrix simulations can be used to expeditiously optimize photocurrent generation in the photoactive region by shaping its absorption spectrum. In this contribution, transfer matrix calculations are shown to effectively guide OPV performance enhancement by spectral tuning in inverted polymer photovoltaic architectures.Since both donor and acceptor materials in the active layer contact both electrodes in BHJ cells, interfacial layers (IFLs) are typically introduced to minimize leakage currents. [ 17 ] In conventional OPV device architectures, where holes are collected at the transparent indium tin oxide (ITO) anode and electrons at the refl ective metal cathode, the archetypical IFL deposited on the ITO is the hole transport layer poly(3,4-ethylenedioxyle nethiophene):poly(styrenesulphonic acid) (PEDOT:PSS). However, this layer limits device lifetime since it is corrosive, [ 18 ] hygroscopic, [ 19 ] and thermally unstable, [ 20 ] motivating alternative IFL materials strategies. Thus, an inverted device architecture (Figure 1 ), where ITO collects electrons and a high work function metal electrode collects holes, has proven very effective in enhancing both OPV performance and durability. [ 21,22 ] In the present work, an electron transport layer (ETL) coating is deposited on the ITO cathode. Solution deposited zinc oxide (ZnO) is a particularly effective ETL in inverted OPVs due to its large bandgap, [ 23 ] high electron mobility, [ 24 ] solar transparency, [ 25 ] and well-positioned conduction band energy for use with electron acceptors, such as fullerene derivatives. [ 26 ] While recent literature has demonstrated higher PCEs using a polymeric ETL in the inverted OPV architecture, [ 27 ] sol-gel ZnO is inexpensive, environmentally friendly, [ 28 ] and a common ETL in inverted OPVs, motivating this study on its impact in optical cavity strategies. [ 29 ] In addition to its favorable ETL properties, ZnO has also been used as an optical spacer [ 30 ] when adjacent to the refl ective metal electrode, improving the distribution of optical intensity in conventional OPVs. In contrast, this work describes the very signifi cant consequences for the optical intensity distribution of placing a ZnO layer adjacent to the transparent electrode in inverted architecture OPVs.The inverted device architecture in this work utilizes a ZnO ETL and a BHJ active layer composed of the donor poly [[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl] [3-fl uoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7) and the acceptor [6,6]-phenyl C 71 butyric acid methyl-ester (PC 71 BM; Figure 1 ). The PTB7:PC 71 BM active layer has been previously shown to yield large internal quantum effi ciencies and exhibit absorption across much of the visible spectrum. [ 31,32 ] Furthermore, this a...

To achieve densely packed charge-selective organosilane-based interfacial layers (IFLs) on the tin-doped indium oxide (ITO) anodes of organic photovoltaic (OPV) cells, a series of Ar2N-(CH2)n-SiCl3 precursors with Ar = 3,4-difluorophenyl, n = 3, 6, 10, and 18, was synthesized, characterized, and chemisorbed on OPV anodes to serve as IFLs. To minimize lateral nonbonded -NAr2···Ar2N- repulsions which likely limit IFL packing densities in the resulting self-assembled monolayers (SAMs), precursor mixtures having both small and large n values are simultaneously deposited. These "heterogeneous" SAMs are characterized by a battery of techniques: contact angle measurements, X-ray reflectivity, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), cyclic voltammetry, and DFT computation. It is found that the headgroup densities of these "supersaturated" heterogeneous SAMs (SHSAMs) are enhanced by as much as 17% versus their homogeneous counterparts. Supersaturation significantly modifies the IFL properties including the work function (as much as 16%) and areal dipole moment (as much as 49%). Bulk-heterojunction OPV devices are fabricated with these SHSAMs: ITO/IFL/poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][2-[[(2-ethylhexyl)oxy]carbonyl]-3-fluorothieno[3,4-b]thiophenediyl]]:phenyl-C71-butyric acid methyl ester (PTB7:PC71BM)/LiF/Al. OPVs having SHSAM IFLs exhibit significantly enhanced performance (PCE by 54%; Voc by 35%) due to enhanced charge selectivity and collection, with the PCE rivaling or exceeding that of PEDOT:PSS IFL devices -7.62%. The mechanism underlying the enhanced performance involves modified hole collection and selectivity efficiency inferred from the UPS data. The ITO/SAM/SHSAM surface potential imposed by the dipolar SAMs causes band bending and favorably alters the Schottky barrier height. Thus, interfacial charge selectivity and collection are enhanced as evident in the greater OPV Voc.