Loading...
Please wait, while we are loading the content...
Similar Documents
Dilemmas of dye-sensitized solar cells.
| Content Provider | Semantic Scholar |
|---|---|
| Author | Bisquert, Juan |
| Copyright Year | 2011 |
| Abstract | Boosted by the urgent need of renewable energies, developments in photovoltaics are turning relatively fast. Just a few years back inorganic thin-film solar cells were a curiosity in a market dominated by crystalline silicon, that now holds about 80 % share mainly due to strong progress of CdTe technology that has grown from 2 % in 2005 to 13 % in 2010. Dye-sensitized solar cells (DSCs) are based on a molecular absorber that emits photogenerated electrons from an excited state to nanostructured TiO2 and receives ground-state electrons from a liquid redox carrier. 2] Since the seminal paper in 1991, a series of efficiency increases were reported, but for many years now, the power conversion efficiency has remained about 11 % in small-area cells. The DSC holds the prospect for a cost-effective photovoltaic technology due to low cost of the raw constituents and easy processability by automated manufacturing, and industrialization activities are showing increasing vigor. However, considering the unavoidable losses in scaling up to module size, higher efficiencies are still required, in robust configurations that ensure a long service life. Rather than conforming to a plateau of frustration, an active and growing research community on DSCs is looking for ways out of it, and there is great expectations to see who will shoot the magic bullet. Herein we discuss the recent development of efficient DSCs based on a new organic dye and ferrocene redox carrier, and to put this new breakthrough into perspective, we first address which are the general weaknesses of DSC that prevent progress. Take the crystalline silicon solar cell as a reference case. The bandgap of silicon is Eg = 1.12 eV, and the optical absorption edge is relatively sharp. Integration of the number of photons above this value with the reference AM1.5G solar spectrum (with total power 100 mW cm , usually termed 1 sun) provides a theoretical current of 43.8 mA cm 2 (see Figure 1). Short-circuit current as high as 42.7 mA cm 2 has been obtained in record cells, which is very close to the theoretical limit. 7] The other crucial element determining power conversion efficiency PCE is the open-circuit voltage Voc. This is given by the separation of electron and hole Fermi levels (EFn and EFp) under photoinduced carrier generation at one sun, and amounts to 0.70 V. The PCE obtained in the record cells is 25 %, that reduces to 19 % in the best commercial modules. In comparison, we look at the key piece of the DSC, the molecular absorbers. Organic absorbers do not absorb equally at all wavelenghts. For example Chlorophyll a, the absorber that nourishes most of the biosphere, has very strong light absorption around 430 and 660 nm but relatively weak absorption bands in the visible region between these wavelengths. It is therefore useful to assess DSC absorbers by the incidentphoton-to-current-conversion efficiency (IPCE), or equivalently, the external-quantum efficiency (EQE). This is the short-circuit current produced by a given dye in an actual DSC device under monochromatic light as a function of wavelength, divided by the theoretical current associated with the incident photon flux. The paradigmatic, ruthenium-based dye Ru(Bu4NHdcbpy)2(NCS)2 known as N719 starts injection at 775 nm, see one example in Figure 1 a. N719 can thus be associated with an effective bandgap of 1.60 eV as noted in Figure 2, which provides for a maximum theoretical photocurrent of 25 mA cm 2 (see Figure 1 b). In practice the photocurrent value must be reduced by about 15 % by the optical transparency of the conducting glass that supports the TiO2 nanoparticle framework and reflection losses. In addition, it is [a] Prof. J. Bisquert Photovoltaics and Optoelectronic Devices Group Departament de F sica, Universitat Jaume I 12071 Castell (Spain) Fax: (+ 34) 964387322 bisquert@fca.uji.es Figure 1. a) Air Mass 1.5 Global (AM1.5G) solar spectrum (photon flux as a function of wavelength) and the measured IPCE of a DSC with N719 dye (PCE 10 %) and a zinc phtalocyanine dye (PCE 1 %). b) Integrated current density as a function of the bandgap energy of the absorber, for AM1.5G solar irradiance. Reference points are shown at 1.10, 1.60 and 1.80 eV. |
| Starting Page | 122 |
| Ending Page | 127 |
| Page Count | 6 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.elp.uji.es/recursos/paper115.pdf |
| PubMed reference number | 21542096v1 |
| Alternate Webpage(s) | https://doi.org/10.1002/cphc.201100248 |
| DOI | 10.1002/cphc.201100248 |
| Journal | Chemphyschem : a European journal of chemical physics and physical chemistry |
| Volume Number | 12 |
| Issue Number | 9 |
| Language | English |
| Access Restriction | Open |
| Subject Keyword | Absorber Device Component Artificial nanoparticles Bands Behavior Cardiomyopathies Dyes Efficiency Eighty Electrons Energy, Physics Femtometer Photons Silicon Weakness cisplatin/cyclophosphamide/etoposide protocol ferrocene light absorption voltage wavelength zinc pyrithione 10 MG/ML Medicated Shampoo |
| Content Type | Text |
| Resource Type | Article |
