From Flat to Nanostructured Photovoltaics: Balance between Thickness of the Absorber and Charge Screening in Sensitized Solar Cells

Boix, Pablo P.,Lee, Yong Hui,Fabregat-Santiago, Francisco,Im, Sang Hyuk,Mora-Sero, Ivan,Bisquert, Juan,Seok, Sang Il American Chemical Society 2012 ACS NANO Vol.6 No.1

<P>Nanoporous metal oxide electrodes provide a high internal area for dye anchoring in dye-sensitized solar cells, but the thickness required to extinguish the solar photons also enhances recombination at the TiO<SUB>2</SUB>/electrolyte interface. The high extinction coefficient of inorganic semiconductor absorber should allow the reduction of the film thickness, improving the photovoltage. Here we study all-solid semiconductor sensitized solar cells, in the promising TiO<SUB>2</SUB>/Sb<SUB>2</SUB>S<SUB>3</SUB>/P3HT configuration. Flat and nanostructured cells have been prepared and analyzed, developing a cell performance model, based on impedance spectroscopy results, that allows us to determine the impact of the reduction of metal oxide film thickness on the operation of the solar cell. Decreasing the effective surface area toward the limit of flat samples produces a reduction in the recombination rate, increasing the open circuit potential, <I>V</I><SUB>oc</SUB>, while providing a significant photocurrent. However, charge compensation problems as a consequence of inefficient charge screening in flat cells increase the hole transport resistance, lowering severely the cell fill factor. The use of novel structures balancing recombination and hole transport will enhance solid sensitized cell performance.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-1/nn204382k/production/images/medium/nn-2011-04382k_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn204382k'>ACS Electronic Supporting Info</A></P>

Overcoming Charge Collection Limitation at Solid/Liquid Interface by a Controllable Crystal Deficient Overlayer

Zhang, Kan,Ravishankar, Sandheep,Ma, Ming,Veerappan, Ganapathy,Bisquert, Juan,Fabregat-Santiago, Francisco,Park, Jong Hyeok Wiley 2017 ADVANCED ENERGY MATERIALS Vol.7 No.3

<P>Bulk and surface charge recombination of photoelectrode are two key processes that significantly hinder solar-to-fuel conversion of photoelectrochemical cell (PEC). In this study, the function of a crystal-deficient overlayer is unveiled, which outperforms a traditionally used amorphous or crystalline overlayer in PEC water splitting by exhibiting a high conductivity and large electron diffusion length to enable unlimited electron collection. The optimized approximate to 2.5 nm thickness of the crystal-deficient shell results in a depletion layer with a width of 3 nm, which overcomes the flat band limitation of the photovoltage and increases the light absorptivity in the wavelength range from 300 to 420 nm. In addition, a 50-fold increase in the conductivity yields a one-order-of-magnitude increase in the diffusion length of an electron (L-n)(approximate to 20 m), allowing for unlimited electron collection in the 1.9 m TiO2 nanowire array with the crystal-deficient shell. The controllable crystal-deficient overlayer in rutile TiO2 nanowires photoanode achieves a photocurrent density greater than 2.0 mA cm(-2) at 1.23 V versus reversible hydrogen electrode (RHE), a 1.18% applied bias photon-to-current efficiency at 0.49 V versus RHE, a faradaic efficiency greater than 93.5% at 0.6 V versus Pt under air mass 1.5G simulated solar light illumination (100 mW cm(-2)).</P>

EFFECT OF THE CHROMOPHORES STRUCTURES ON THE PERFORMANCE OF SOLID-STATE DYE SENSITIZED SOLAR CELLS

HAINING TIAN,Eva M. Barea,ANDREA SOTO,BO XU,LICHENG SUN,ANDERS HAGFELDT,FRANCISCO FABREGAT-SANTIAGO,IVAN MORA-SERO,강용수,Juan Bisquert 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2014 NANO Vol.9 No.5

The efect of metal-free chromophores on dye-sensitized solar cell performance is investigated. Solid state dye-sensitized solar cells (ssDSCs) using diferent molecular sensitizers based on tri-phenylamine (TPA) with thiophene linkers and diferent alkyl chain in the donor unit have beencharacterized using impedance spectroscopy (IS). We show that diferent molecular structuresplay a fundamental role on solar cell performance, by the efect produced on TiO 2 conductionband position and in the recombination rate. Dye structure and its electronic properties are themain factors that control the recombination, the capacitance and the e±ciency of the cells. Aclear trend between the performance of the cell and the optimization level of the blocking efect of the dye structure has been identi¯ed in the solid state solar cells with Spiro-OMeTAD holeconductor.

Three dimensional-TiO₂ nanotube array photoanode architectures assembled on a thin hollow nanofibrous backbone and their performance in quantum dot-sensitized solar cells

Han, Hyungkyu,Sudhagar, P.,Song, Taeseup,Jeon, Yeryung,Mora-Seró,, Ivá,n,Fabregat-Santiago, Francisco,Bisquert, Juan,Kang, Yong Soo,Paik, Ungyu The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.27

<P>Facile synthesis of TiO<SUB>2</SUB> nanotube branched (length ∼0.5 μm) thin hollow-nanofibers is reported. The hierarchical three dimensional photoanodes (H-TiO<SUB>2</SUB>-NFs) (only ∼1 μm thick) demonstrate their excellent candidature as photoanodes in QD-sensitized solar cells, exhibiting ∼3-fold higher energy conversion efficiency (<I>η</I> = 2.8%, <I>J</I><SUB>sc</SUB> = 8.8 mA cm<SUP>−2</SUP>) than that of the directly grown nanotube arrays on a transparent conducting oxide (TCO) substrate (<I>η</I> = 0.9%, <I>J</I><SUB>sc</SUB> = 2.5 mA cm<SUP>−2</SUP>).</P> <P>Graphic Abstract</P><P>Facile synthesis of TiO<SUB>2</SUB> nanotube branched (length ∼0.5 μm) thin hollow-nanofibers is reported. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc40439k'> </P>

Interfacial engineering of quantum dot-sensitized TiO₂ fibrous electrodes for futuristic photoanodes in photovoltaic applications

Sudhagar, P.,Gonzá,lez-Pedro, Victoria,Mora-Seró,, Ivá,n,Fabregat-Santiago, Francisco,Bisquert, Juan,Kang, Yong Soo The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.28

<P>Herein we report generic surface treatment approaches to improve the electronic interfaces of quantum dot-sensitized TiO<SUB>2</SUB> fiber electrodes, thereby promoting their photoanode performance. Highly dense, continuous and nanostructured TiO<SUB>2</SUB> fibrous membranes, without the inclusion of a scattering layer, unlike conventional TiO<SUB>2</SUB> particulate electrodes, showed feasible photoconversion performance under the proposed interfacial engineering modification. The proposed interfacial treatment concerns fibrous membranes both before and after calcination. The chemical vapor pre-treatment on an as-deposited fibrous membrane using tetrahydrofuran (THF) reinforces the physical contact between the fibrous membrane and the transparent conducting substrate and reduces significantly the recombination rate. In the case of post-treatment by F-ion on a fibrous surface, together with the interfacial engineering approach, the ZnS surface passivation layer markedly improves the photoanode performance of the TiO<SUB>2</SUB> fibrous membrane nearly to a factor of 3.2% with a remarkable open-circuit voltage <I>V</I><SUB>oc</SUB> = 0.69 V and <I>J</I><SUB>sc</SUB> = 13 mA cm<SUP>−2</SUP> under 1 sun illumination (100 mW cm<SUP>−2</SUP>). This report provides an excellent platform for studying and understanding the interfacial contacts and mechanisms related to the charge transfer at CdS/CdSe QD-sensitized TiO<SUB>2</SUB> fibrous assemblies. Such implications of this interfacial treatment strategy can be successfully extended to a wide range of photoanode candidates in energy conversion systems and confirm the effectiveness of some alternative nanostructured electrodes for the development of semiconductor-sensitized solar cells.</P> <P>Graphic Abstract</P><P>The generic surface treatment approaches were demonstrated to improve the electronic interfaces of quantum dot-sensitized TiO<SUB>2</SUB> fiber electrodes, thereby improving their photoanode performance in solar cells. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm31599h'> </P>

Electron-Transfer Kinetics through Interfaces between Electron-Transport and Ion-Transport Layers in Solid-State Dye-Sensitized Solar Cells Utilizing Solid Polymer Electrolyte

Cho, Woohyung,Lim, Jongchul,Kim, Tea-Yon,Kim, Young Rae,Song, Donghoon,Park, Taiho,Fabregat-Santiago, Francisco,Bisquert, Juan,Kang, Yong Soo American Chemical Society 2016 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.120 No.5

<P>The origin of the differences between the performance parameters found for dye-sensitized solar cells (DSCs) using liquid and poly(ethylene oxide)-based solid polymer electrolytes has been investigated. Limitations associated with poor polymer electrolyte penetration and ionic diffusion have been analyzed together with other effects such as the dye regeneration rate, the conduction band edge shift, and the electron recombination kinetics occurring in the solid polymer electrolyte. We have found that dye regeneration was faster for sensitized TiO2 films fully wetted with polymer electrolyte than that with liquid cells. This new result was attributed to a 0.2 eV decrease in the dye highest occupied molecular orbital energy yielding to an increase in the driving force for dye regeneration. These understandings may contribute to a further increase in the energy-conversion efficiency of DSCs employing solid polymer electrolyte.</P>

Chemical Effects of Tin Oxide Nanoparticles in Polymer Electrolytes-Based Dye-Sensitized Solar Cells

Chae, Hwaseok,Song, Donghoon,Lee, Yong-Gun,Son, Taewook,Cho, Woohyung,Pyun, Yong Bum,Kim, Tea-Yon,Lee, Jung Hyun,Fabregat-Santiago, Francisco,Bisquert, Juan,Kang, Yong Soo American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.30

<P>The effects on the photovoltaic performance of the incorporation of SnO<SUB>2</SUB> nanoparticles into the polymer of a solid-state dye-sensitized solar cell (DSC) based on the poly(ethylene oxide)/poly(ethylene glycol) dimethyl ether solid electrolyte are studied in this paper. It has been found that the addition of SnO<SUB>2</SUB> nanoparticles to the solid electrolyte produces several key changes in the properties of the solid-state DSC that produced a better performance of the device. Therefore, we have measured an improvement in electrolyte conductivity by a factor of 2, a linear rise in the TiO<SUB>2</SUB> conduction band position, a reduction in the electron recombination rate, and a decrease in charge-transfer resistance at the counterlectrode/electrolyte interface. All these improvements produced an increase in the power conversion efficiency from 4.5 to 5.3% at 1 sun condition, a consequence of the increase of both <I>V</I><SUB>oc</SUB> (oc = open circuit) and <I>J</I><SUB>sc</SUB> (sc = short circuit) without any sacrifice in FF (fill factor)<I>.</I> The origin of these changes has been associated to the strong Lewis acidic character of SnO<SUB>2</SUB> nanoparticles yielding to the formation of a I<SUB>3</SUB><SUP>–</SUP> percolation layer for holes at the surface of SnO<SUB>2</SUB> and the reduction of the concentration of free I<SUB>3</SUB><SUP>–</SUP> and K<SUP>+</SUP> ions inside the pores of TiO<SUB>2</SUB>. From these results, it is concluded that the physicochemical effects of inorganic nanofiller in the polymer electrolyte may also be considered a good route in designing the high efficiency solid-state DSCs employing the polymer electrolyte.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-30/jp4117485/production/images/medium/jp-2013-117485_0012.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp4117485'>ACS Electronic Supporting Info</A></P>