Lead-Free Perovskite and Improved Processes and Techniques for Creating Future Photovoltaic Cell to Aid Green Mobility

Perovskites material is in the spotlight as photovoltaic device due to their optical and physical properties. In a short period of time, this organic-inorganic pevskite can achieve about energy conversion efficiencies of 25.6% by anti-solvent and spin-coating based process. In addition, ambipolar carrier transport properties of perovskite materials open up new directions for the high-efficiency thin-film solar cells. Despite its attractive properties in solar cell application, concerned about device stability and the use of lead compounds (APbX3, A = a cation X = halide) with toxicity cause the potential risk for the human body and environment issue. Therefore, the use of a new classed strucutral materials with intrinsic stability and beneficial optoelectronic properties can be considered as a start of the next chapter in pervoksite device. This chapter is structured into two major parts: In section 1, we introduce more stable class of perovskite, A2SnX6, where Sn is in the 4+ oxidation state. A detailed discussion on the ramifications of material structure and chemistry-related challenges is presented for solution processing, along with careful characterization. In section 2, we talk about the direction of development for perovksite materials to be a next chapter of energy source for a green mobility

A New Generation of Energy Harvesting Devices

This chapter has been mainly focused on the development and fabrication of various nanostructured materials for electrochemical energy conversion, specially, third generation (3rd) thin film photovoltaic system such as organic dye or perovskite -sensitized Solar Cells. Enormous efforts have been dedicated to the development of a variety of clean energy, capable of harvesting energy of various forms. Among the various energy forms, electrochemical devices that produce electric energy from chemical energy have received the most attention as the most promising power sources. In the majority of cases, researchers who come from the different background could engage on certain aspects of the components to improve the photovoltaic performances from different disciplines: (i) chemists to design and synthesize suitable donor–acceptor dyes and study structure–property relationships; (ii) physicists to build solar cell devices with the novel materials, to characterize and optimize their performances, and to understand the fundamental photophysical processes; and (iii) engineers to develop new device architectures. The synergy between all the disciplines will play a major role for future advancements in this area. However, the simultaneous development of all components such as photosensitizers, hole transport layer, photoanodes and cost effective cathode, combined with further investigation of transport dynamics, will lead to Photovoltaic cells, 30%. Herein, in this book, with taking optimized processing recipe as the standard cell fabrication procedure, imporant breakthough for each components is achieved by developing or designing new materials, concepts, and fabrication technique. This book report the following studies: (i) a brief introduction of the working principle, (ii) the detailed study of the each component materials, mainly including TiO2 photoanode under the category of 0D and 3D structures, strategies for co-sensitization with porphyrin and organic photosensitizers, and carbon catalytic material via controlled fabrication protocols and fundamental understanding of the working principles of electrochemical photovoltaic cell has been gained by means of electrical and optical modelling and advanced characterization techniques and (iii) new desgined stratages such as the optimization of photon confinement (iv) future prospects and survival stratagies for sensitizer assisted solar cell (especially, DSSC)

Efficiency enhancement in solid dye-sensitized solar cell by three-dimensional photonic crystal

Dye-sensitized solar cells (DSSCs) offer an attractive alternative to conventional solar cells because of their lower production cost. However, the liquid electrolyte used in these cells is unstable because of solvent leakage or evaporation, and DSSCs that use a solid electrolyte do not perform as well. In this paper, we present a design in which a nanocrystal (nc)-TiO2 underlayer is integrated with an optically active porous three dimensional photonic crystals (3D PCs) overlayer, and a sequential infiltration process is adopted to introduce additives to the solid electrolyte. This architecture allows effective dye sensitization, electrolyte infiltration, and charge collection from both the nc-TiO2 and the PC layers, yielding enhanced absorption in a specific spectral region. We describe the fabrication process and demonstrate the improved performance of the fabricated DSSCs, which exhibited conversion efficiencies that were as much as 32% higher than those of a conventional DSSC. This approach should be useful in solid-state devices where pore infiltration is a limiting factor, as well as in weakly absorbing photovoltaic devices. © 2013 The Royal Society of Chemistry.FALS

Efficiency Enhancement in Dye-Sensitized Solar Cells by Three-Dimensional Photonic Crystals

We have proposed a new dye-sensitized solar cell (DSSC) structure that employs three-dimensional (3D) photonic crystals (PCs) to enhance the light absorption and improve the power conversion efficiency (PCE) by using coherent scattering phenomena. All the DSSC structures with the 3D PC layer exhibited higher short-circuit current densities and higher PCE (10.8%) than those of traditional DSSCs (9.5%) because light that passed through the photoanode was diffracted, thereby making it possible to reuse it. The PCE is improved without affecting the delicate kinetic balance between the charge separation and recombination that is required to improve light-harvesting efficiency (LHE). © 2012 The Japan Society of Applied Physics.

Cross-Linkable Molecular Hole-Transporting Semiconductor for Solid-State Dye-Sensitized Solar Cells

In this study, we investigate the use of a cross-linkable organosilane semiconductor, 4,4′-bis­[(<i>p</i>-trichlorosilylpropylphenyl)­phenylamino]­biphenyl (TPDSi₂), as a hole-transporting material (HTM) for solid-state dye-sensitized solar cells (ssDSSCs) using the standard amphiphilic Z907 dye which is compatible with organic HTM deposition. The properties and performance of the resulting cells are then compared and contrasted with the ones based on poly­(3-hexylthiophene) (P3HT), a conventional polymeric HTM, but with rather limited pore-filling capacity. When processed under N₂, TPDSi₂ exhibits excellent infiltration into the mesoporous TiO₂ layer and thus enables the fabrication of relatively thick devices (∼5 μm) for efficient photon harvesting. When exposed to ambient atmosphere (RH_amb ∼ 20%), TPDSi₂ readily undergoes cross-linking to afford a rigid, thermally stable hole-transporting layer. In addition, the effect of <i>tert</i>-butylpyridine (TBP) and lithium bis­(trifluoromethylsulfonyl)­imide salt (Li-TFSI) additives on the electrochemical properties of these HTMs is studied via a combination of cyclic voltammetry (CV) and ultraviolet photoemission spectroscopy (UPS) measurements. The results demonstrate that the additives significantly enhance the space charge limited current (SCLC) mobilities for both the P3HT and TPDSi₂ HTMs and induce a shift in the TPDSi₂ Fermi level, likely a p-doping effect. These combined effects of improved charge transport characteristics for the TPDSi₂ devices enhance the power conversion efficiency (PCE) by more than 2-fold for ssDSSCs

Air-Stable Molecular Semiconducting Iodosalts for Solar Cell Applications: Cs₂SnI₆ as a Hole Conductor

We introduce a new class of molecular iodosalt compounds for application in next-generation solar cells. Unlike tin-based perovskite compounds CsSnI₃ and CH₃NH₃SnI₃, which have Sn in the 2+ oxidation state and must be handled in an inert atmosphere when fabricating solar cells, the Sn in the molecular iodosalt compounds is in the 4+ oxidation state, making them stable in air and moisture. As an example, we demonstrate that, using Cs₂SnI₆ as a hole transporter, we can successfully fabricate in air a solid-state dye-sensitized solar cell (DSSC) with a mesoporous TiO₂ film. Doping Cs₂SnI₆ with additives helps to reduce the internal device resistance, improving cell efficiency. In this way, a Z907 DSSC delivers 4.7% of energy conversion efficiency. By using a more efficient mixture of porphyrin dyes, an efficiency near 8% with photon confinement has been achieved. This represents a significant step toward the realization of low-cost, stable, lead-free, and environmentally benign next-generation solid-state solar cells

Metal-Free Tetrathienoacene Sensitizers for High-Performance Dye-Sensitized Solar Cells

A new series of metal-free organic chromophores (TPA-TTAR-A (<b>1</b>), TPA-T-TTAR-A (<b>2</b>), TPA-TTAR-T-A (<b>3</b>), and TPA-T-TTAR-T-A (<b>4</b>)) are synthesized for application in dye-sensitized solar cells (DSSC) based on a donor-π-bridge-acceptor (D−π–A) design. Here a simple triphenylamine (TPA) moiety serves as the electron donor, a cyanoacrylic acid as the electron acceptor and anchoring group, and a novel tetrathienoacene (TTA) as the π-bridge unit. Because of the extensively conjugated TTA π-bridge, these dyes exhibit high extinction coefficients (4.5–5.2 × 10⁴ M^–1 cm^–1). By strategically inserting a thiophene spacer on the donor or acceptor side of the molecules, the electronic structures of these TTA-based dyes can be readily tuned. Furthermore, addition of a thiophene spacer has a significant influence on the dye orientation and self-assembly modality on TiO₂ surfaces. The insertion of a thiophene between the π-bridge and the cyanoacrylic acid anchoring group in TPA-TTAR-T-A (dye <b>3</b>) promotes more vertical dye orientation and denser packing on TiO₂ (molecular footprint = 79 Ų), thus enabling optimal dye loading. Using dye <b>3</b>, a DSSC power conversion efficiency (PCE) of 10.1% with <i>V</i>_oc = 0.833 V, <i>J</i>_sc = 16.5 mA/cm², and FF = 70.0% is achieved, among the highest reported to date for metal-free organic DSSC sensitizers using an I^–/I₃^– redox shuttle. Photophysical measurements on dye-grafted TiO₂ films reveal that the additional thiophene unit in dye <b>3</b> enhances the electron injection efficiency, in agreement with the high quantum efficiency