Fabrication and characterization of evaporated hybrid perovskite based solar cells

International audienceOver the last years, interest for hybrid perovskite materials as light absorber in photovoltaic devices has increased continuously, from only 14 publications in 2012 to over 2200 in 2016 [1]. Hybrid perovskite deposition techniques can be sort out in two families: wet processing and vacuum deposition. If the first is the most widely used, the second appears more suitable for future commercialization of perovskite solar cells. Indeed, wet processing is highly user dependant and hardly allows homogeneous large surface deposition when vacuum based deposition permits high reproducibility between batches and homogeneity over large area. In this context we report here experimental details to fabricate evaporated hybrid perovskite films including material densities, heating temperatures and deposition rates. The obtained layers will be characterized by absorption spectra, XRD (X-Ray Diffraction) or SEM (Scanning Electron Microscopy). Evaporated hybrid perovskite layers will also be incorporated in photovoltaic devices (structure being ITO/PEDOT:PSS/Perovskite/PCBM/Ag) and characterized by J-V and EQE (External Quantum Efficiency) measurements

Perovskites hybrides par évaporation pour des cellules solaires à hauts rendements

International audienceDepuis 2009, les matériaux perovskites de structure ABX 3 (où A est un cation organique, B un métal et X un halogène) attirent de plus en plus d'intérêt dans le domaine du photovoltaïque. En effet, en moins d'une décennie les rendements ont augmentés de 3.9 % à plus de 22 %, une progression qu'aucune autre technologie PV n'a jamais connue. Ces incroyables matériaux peuvent être obtenus par voie liquide (en une [3] ou deux [4] étapes(s)) ou par différentes techniques par voie sèche. En 2013, Snaith et al. [5] publient une étude comparative entre la voie liquide une étape et la co-évaporation en voie sèche. Pour un même matériau MAPbl_{3-x] Cl$_x$ , les dispositifs à base de couches évaporées atteignent 15.4 % d'efficacité contre 8.6 % pour les dispositifs à base de dépôts en voie liquide. Si actuellement la grande majorité des travaux porte sur la voie liquide, les techniques par voie sèche apparaissent comme les plus adaptées à une future industrialisation des procédés. En effet, celles-ci permettent une meilleure homogénéité sur des larges surfaces. En partant de différents précurseurs tels que CH$_3$ NH$_3$I, CH(NH$_2$)$_2$I ou CH$_3$ NH$_3$ Br et Pbl$_2$ ou PbBr$_2$ , différents films de perovskites sont obtenus par co-évaporation. Ceux-ci sont ensuite intégrés dans des cellules solaires de structures variées.

Study of different hole transporting materials for hybrid perovskite solar cells

International audienceOver the last years, interest for organolead trihalide perovskite materials (ABX3 where A is an ammonium cation, B a metal cation and X an halide) as light absorber in solar cells has increased continuously [1]. One of the most studied hybrid perovskite material is methylammonium lead triiodide (MAPbI3) leading to 15 to 20% efficiencies in a FTO/TiO2/mp-TiO2/MAPbI3/Au structure [2,3]. A new method for preparation and one-step process deposition of the perovskite material [4] is here used in a planar heterojunction FTO/compact-TiO2/MAPbI3/HTM/Au structure leading to 11% efficiency (on 0.28 cm² cell) when Spiro-MeOTAD is used as HTM (J/V curve Figure 1 (left)). Five new spiro-based HTM (Figure 1 (right)) are then compared to this reference system

Study of different hole transporting materials for hybrid perovskite solar cells

International audienceOver the last years, interest for organolead trihalide perovskite materials (ABX3 where A is an ammonium cation, B a metal cation and X an halide) as light absorber in solar cells has increased continuously [1]. One of the most studied hybrid perovskite material is methylammonium lead triiodide (MAPbI3) leading to 15 to 20% efficiencies in a FTO/TiO2/mp-TiO2/MAPbI3/Au structure [2,3]. A new method for preparation and one-step process deposition of the perovskite material [4] is here used in a planar heterojunction FTO/compact-TiO2/MAPbI3/HTM/Au structure leading to 11% efficiency (on 0.28 cm² cell) when Spiro-MeOTAD is used as HTM (J/V curve Figure 1 (left)). Five new spiro-based HTM (Figure 1 (right)) are then compared to this reference system

Spirobifluorene based small push-pull molecules for organic photovoltaic applications

International audienceFour analogous push-pull systems have been synthesized. If the latter all involve the same electron rich diphenylamine termination (D) and π-conjugating spacer (p) they differ from their electron withdrawing groups (A) and more importantly by their linear or 3D structure. Indeed, two push-pull spirobifluorene derivatives, which present two perpendicular D-p-A systems by molecule, are compared to their linear analogues. After description of their syntheses, spectroscopic and electrochemical properties, comforted by theoretical calculations, are discussed and compared. Then, a preliminary evaluation of compounds as active materials in organic solar cells is presented and demonstrates the potential interest of spiro-based derivatives for organic photovoltaics

Low-temperature deposition of transparent conductive layers for perovskite-silicon tandem cells

International audienceSince 2013, single-junction research-cell power conversion efficiencies of perovskite cells have risen by about 8%$_{abs}$ to 22.1%, while multicrystalline silicon and monocrystalline silicon efficiencies have risen by less than 2% abs and less than 1% abs , respectively Tandem cells with a perovskite top cell and a silicon bottom cell, recently achieving 23.6% in two-terminal configuration, present a promising alternative to further increase the relatively stagnant performance of already highly-optimized single-junction silicon cells. To facilitate such an advance, methods to deposit high-quality transparent conductors (TCs) which do not subject the perovskite layer to degradation during deposition need to be found. We utilize a spin-coating solution deposition process optimized for high reproducibility, yielding the single-junction MAPbl$_{3-x}$ Cl x perovskite cell stack shown in Figure 1, with an average efficiency of 7.94 $\pm$ 0.68 % with a non-transparent electrode. Two different TC electrodes are tested on these cells: evaporated thin-film semi-transparent Ag layers and low-temperature RF-sputtered indium tin oxide layers. For the latter, buffer layers of either thin-film Ag, Ag/BCP, Ag nanowires or interlinked PCBM are used to protect the organic layer stack from sputtering damage. By comparing transparency and efficiency, we will identify the most suitable approac

Low-temperature deposition of transparent conductive layers for perovskite-silicon tandem cells

International audienceSince 2013, single-junction research-cell power conversion efficiencies of perovskite cells have risen by about 8%$_{abs}$ to 22.1%, while multicrystalline silicon and monocrystalline silicon efficiencies have risen by less than 2% abs and less than 1% abs , respectively Tandem cells with a perovskite top cell and a silicon bottom cell, recently achieving 23.6% in two-terminal configuration, present a promising alternative to further increase the relatively stagnant performance of already highly-optimized single-junction silicon cells. To facilitate such an advance, methods to deposit high-quality transparent conductors (TCs) which do not subject the perovskite layer to degradation during deposition need to be found. We utilize a spin-coating solution deposition process optimized for high reproducibility, yielding the single-junction MAPbl$_{3-x}$ Cl x perovskite cell stack shown in Figure 1, with an average efficiency of 7.94 $\pm$ 0.68 % with a non-transparent electrode. Two different TC electrodes are tested on these cells: evaporated thin-film semi-transparent Ag layers and low-temperature RF-sputtered indium tin oxide layers. For the latter, buffer layers of either thin-film Ag, Ag/BCP, Ag nanowires or interlinked PCBM are used to protect the organic layer stack from sputtering damage. By comparing transparency and efficiency, we will identify the most suitable approac

Poly(2‐vinylpyridine) as an Additive for Enhancing N‐Type Organic Thin‐Film Transistor Stability

Abstract N‐type organic semiconductors are particularly susceptible to degradation by ambient air. One such solution to this issue is to include additives in the inks these semiconductors would be cast from that would enhance device stability after film deposition. This method would reduce the number of processing steps needed to fabricate devices compared to other stabilization methods, such as encapsulation. In this study, the stabilization of n‐type performance of the semiconductor poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,29‐bisthiophene)} (P(NDI2OD‐T2)) when it is blended with an increasing proportion by weight of poly(2‐vinylpyridine) (P2VP) is reported. The simple synthesis of P2VP also makes it an ideal candidate material for large‐scale applications. Concentrations as low as 0.1% P2VP incorporated into the P(NDI2OD‐T2) blends provided an immediate stabilization effect, and at 10% and 50%, longer‐term stability after one week is observed

Anharmonicity in Hybrid and Inorganic Perovskite Materials used for Photovoltaics Applications References

International audienceHybrid organic-inorganic perovskite materials have emerged over the past five years as absorber layers for new high-efficiency yet low-cost solar cells that combine the advantages of organic and inorganic semiconductors. Despite this sky rocketing evolution, the physics behind the electronic transport in these materials is still poorly understood. Here, employing the linear response (DFPT) approach of Density Functional Theory (DFT) and frozen phonon calculations, we reveal strong anharmonic effects in the inorganic CsPbI$_3$ perovskite structure compared to the hybrid CH$_3$ NH$_3$ PbI$_3$ (MAPbI$_3$) material, and found a double-well instability at the center of the Brillouin Zone. We show that previously reported soft modes are stabilized at the actual lower symmetry equilibrium structure, which occurs in a very flat energy landscape. These findings highlight the crucial role played by temperature in these materials, showing that this perovskite structure can oscillate between two equilibrium states at room temperature. Taking into account these low energy-highly occupied phonon states into the models used for electron-phonon interactions and band gap calculations could lead to a better understanding of the electrical transport properties of perovskite solar cells

Metal halide perovskite layers studied by scanning transmission X-ray microscopy

International audienceWe describe the investigation of metal halide perovskite layers, particularly CH3NH3PbI3 used in photovoltaic applications, by soft X-ray scanning transmission X-ray microscopy (STXM). Relevant reference spectra were used to fit the experimental data using singular value decomposition. The distribution of key elements Pb, I, and O was determined throughout the layer stack of two samples prepared by wet process. One sample was chosen to undergo electrical biasing. Spectral data shows the ability of STXM to provide relevant chemical information for these samples. We found the results to be in good agreement with the sample history, both regarding the deposition sequence and the degradation of the perovskite material