70 research outputs found
Optimization of a high work function solution processed vanadium oxide hole-extracting layer for small molecule and polymer organic photovoltaic cells
We report a method of fabricating a high work function, solution processable vanadium oxide (V2Ox(sol)) hole-extracting layer. The atmospheric processing conditions of film preparation have a critical influence on the electronic structure and stoichiometry of the V2Ox(sol), with a direct impact on organic photovoltaic (OPV) cell performance. Combined Kelvin probe (KP) and ultraviolet photoemission spectroscopy (UPS) measurements reveal a high work function, n-type character for the thin films, analogous to previously reported thermally evaporated transition metal oxides. Additional states within the band gap of V2Ox(sol) are observed in the UPS spectra and are demonstrated using X-ray photoelectron spectroscopy (XPS) to be due to the substoichiometric nature of V2Ox(sol). The optimized V2Ox(sol) layer performance is compared directly to bare indiumâtin oxide (ITO), poly(ethyleneoxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and thermally evaporated molybdenum oxide (MoOx) interfaces in both small molecule/fullerene and polymer/fullerene structures. OPV cells incorporating V2Ox(sol) are reported to achieve favorable initial cell performance and cell stability attributes
Efficient Organic Photovoltaics Utilizing Nanoscale Heterojunctions in Sequentially Deposited Polymer/fullerene Bilayer
A highly efficient sequentially deposited bilayer (SD-bilayer) of polymer/fullerene organic photovoltaic (OPV) device is developed via the solution process. Herein, we resolve two essential problems regarding the construction of an efficient SD-bilayer OPV. First, the solution process fabrication of the SD-bilayer is resolved by incorporating an ordering agent (OA) to the polymer solution, which improves the ordering of the polymer chain and prevents the bottom-layer from dissolving into the top-layer solution. Second, a non-planar heterojunction with a large surface area is formed by the incorporation of a heterojunction agent (HA) to the top-layer solution. Poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole- 4,7-diyl-2,5-thiophenediyl] (PCDTBT) is used for the bottom-layer and phenyl-C71-butyric-acid-methyl ester (PC70BM) is used for the top-layer. The SD-bilayer OPV produced utilizing both an OA and HA exhibits a power conversion efficiency (PCE) of 7.12% with a high internal quantum efficiency (IQE). We believe our bilayer system affords a new way of forming OPVs distinct from bulk heterojunction (BHJ) systems and offers a chance to reconsider the polymers that have thus far shown unsatisfactory performance in BHJ systemsope
Fully spray-coated triple-cation perovskite solar cells
We use ultrasonic spray-coating to sequentially deposit thin films of tin oxide, a triple-cation perovskite and spiro-OMeTAD, allowing us fabricate perovskite solar cells (PSCs) with a champion reverse scan power conversion efficiency (PCE) of 19.4% on small-area substrates. We show that the use of spray-deposition permits us to rapidly (>80âmmâsâ1) coat 25âmm Ă 75âmm substrates that were divided into a series of devices each with an active area of 15.4 mm2, yielding an average PCE of 10.3% and a peak PCE of 16.3%. By connecting seven 15.4 mm2 devices in parallel on a single substrate, we create a device having an effective active area of 1.08 cm2 and a PCE of 12.7%. This work demonstrates the possibility for spray-coating to fabricate high efficiency and low-cost perovskite solar cells at speed
P3HT-Based Solar Cells: Structural Properties and Photovoltaic Performance
Each year we are bombarded with B.Sc. and Ph.D. applications from students that want to improve the world. They have learned that their future depends on changing the type of fuel we use and that solar energy is our future. The hope and energy of these young people will transform future energy technologies, but it will not happen quickly. Organic photovoltaic devices are easy to sketch, but the materials, processing steps, and ways of measuring the properties of the materials are very complicated. It is not trivial to make a systematic measurement that will change the way other research groups think or practice. In approaching this chapter, we thought about what a new researcher would need to know about organic photovoltaic devices and materials in order to have a good start in the subject. Then, we simplified that to focus on what a new researcher would need to know about poly-3-hexylthiophene:phenyl-C61-butyric acid methyl ester blends (P3HT: PCBM) to make research progress with these materials. This chapter is by no means authoritative or a compendium of all things on P3HT:PCBM. We have selected to explain how the sample fabrication techniques lead to control of morphology and structural features and how these morphological features have specific optical and electronic consequences for organic photovoltaic device applications
Critical Interface States Controlling Rectification of Ultrathin NiOâZnO pân Heterojunctions
Herein, we consider
the heterojunction formation of two prototypical metal oxides: p-type
NiO and n-type ZnO. Elementally abundant, low-cost metal oxide/oxideâ
heterojunctions are of interest for UV optical sensing, gas sensing,
photocatalysis, charge confinement layers, piezoelectric nanogenerators,
and flash memory devices. These heterojunctions can also be used as
current rectifiers and potentially as recombination layers in tandem
photovoltaic stacks by making the two oxide layers ultrathin. In the
ultrathin geometry, understanding and control of interface electronic
structure and chemical reactions at the oxide/oxideâ interface
are critical to functionality, as oxygen atoms are shared at the interface
of the dissimilar materials. In the studies presented here the extent
of chemical reactions and interface band bending is monitored using
X-ray and ultraviolet photoelectron spectroscopies. Interface reactivity
is controlled by varying the near surface composition of nickel oxide,
nickel hydroxide, and nickel oxyhydroxide using standard surface-treatment
procedures. A direct correlation between relative percentage of interface
hydroxyl chemistry (and hence surface Lewis basicity) and the local
band edge alignment for ultrathin pân junctions (6 nm NiO/30
nm ZnO) is observed. We propose an acidâbase formulism to explain
these results: the stronger the acidâbase reaction, the greater
the fraction of interfacial electronic states which lower the band
offset between the ZnO conduction band and the NiO valence band. Increased
interfacial gap states result in larger reverse bias current of the
pân junction and lower rectification ratios. The acidâbase
formulism could serve as a future design principle for oxide/oxideâ
and other heterojunctions based on dissimilar materials
- âŠ