Yoshikazu Furumoto

Ionic liquid-assisted growth of methylammonium lead iodide spherical nanoparticles by a simple spin-coating method and photovoltaic properties of perovskite solar cells

Hybrid organometal halide perovskites such as methylammonium lead iodide (MAPbI3) are a promising class of cost- and energy-efficient light absorption materials for thin-film photovoltaics. In this work, the preparation and characterization of MAPbI3 nanoparticles (NPs) on TiOx/indium tin oxide glass substrates using a simple spin-coating technique have been investigated. The NPs were prepared by spin-coating solutions of MAPbI3 and the ionic liquid (IL) 1-hexyl-3-methylimidazolium chloride in N,N-dimethylformamide. Analysis of the resulting spin-coated films revealed that uniform spherical MAPbI3 NPs with an average diameter of 540 nm were homogeneously distributed on the TiOx substrates. MAPbI3 films with similar crystallinity were observed irrespective of the inclusion of IL, as evident from the X-ray diffraction patterns of the films. However, addition of IL to the spin-coating solution facilitated the formation of homogenous nucleation sites and prevented rapid crystal formation of MAPbI3. Therefore, the presence of an IL resulted in uniform thin films with good morphology.

Annealing effects on CsPbI3-based planar heterojunction perovskite solar cells formed by vacuum deposition method

Cesium iodide (CsI) is attracting attention as a substitute for organic materials such as CH3NH3I. In this work, we fabricated sequential-vacuum-deposited planar heterojunction (PHJ) cesium lead iodide (CsPbI3) perovskite solar cells with enhanced efficiencies by varying the annealing time (0.5, 1, 5, and 10 min). The effect of performance enhancement was investigated as a function of varying annealing time at 350 °C employing a hot plate. The best-performing device was obtained with an annealing time of 1 min, delivered photocurrent density (J SC) of 12.06 mA/cm2, voltage (V OC) of 0.71 V, and fill factor (FF) of 0.67, leading to a power conversion efficiency (PCE) of 5.71% at standard AM 1.5G solar illumination.

Degradation mechanism for planar heterojunction perovskite solar cells

Organic–inorganic hybrid perovskite materials have recently emerged as a promising cost- and energy-efficient light absorber material for photovoltaic applications. Unfortunately, perovskite solar cells have a problem with decreasing power conversion efficiency owing to their degradation in air. To clarify the cause of the degradation of perovskite solar cells, we exposed deposited CH3NH3PbI3 and HC(NH2)2PbI3 films to an O2 or (H2O+N2) atmosphere condition. Analysis of these films revealed that a large energy band gap was observed as a result of the influence of the H2O molecule in CH3NH3PbI3 and HC(NH2)2PbI3. Under the (H2O+N2) atmosphere condition, the existence of CH3NH3I and HC(NH2)2I molecules was found to affect the morphology and as well as the crystalline diffraction peak. The resultant perovskite crystalline structure was degraded by H2O molecules under the air exposure condition.

Shape-controlled CH3NH3PbI3 nanoparticles for planar heterojunction perovskite solar cells

Hybrid organic/inorganic perovskites such as methylammonium lead iodide (CH3NH3PbI3) are potential candidates for thin-film photovoltaics because of their excellent cost- and energy-efficient light absorption. In this work, we have prepared CH3NH3PbI3 nanoparticles (NPs) on the TiOx/ITO glass substrates by a simple spin-coating method to control the size and shape of NPs. The effect of varying the weight percentage (wt %) of ionic liquid (IL) has also been investigated. Analysis of the films revealed spherical NP morphology in the presence of 1, 3, and 7 wt % IL with respective diameters of 540, 350, and 600 nm. Conversely, 10 wt % IL resulted in irregular aggregation of NP blocks. The power conversion efficiency (PCE) changed upon varying the NP size, shape, and morphology. The optimization of the concentration with 3 wt % IL yielded NPs with the most uniform shape, size, and morphology and, consequently, the maximum PCE.

Planar heterojunction type perovskite solar cells based on TiOx compact layer fabricated by chemical bath deposition

Perovskite (CH3NH3PbI3) solar cell (PSC) have been recently emerged as a promising cost and energy efficient light absorber material for photovoltaic applications. In this paper, we fabricated planar heterojunction (PHJ) perovskite solar cells using chemical bath deposited low temperature titanium oxide (TiOx) compact layer as an electron collection layer. The devices modified by fullerene (C60) with the thickness of 7nm show very significant improvement in photovoltaic performances compared to without modified devices leading to efficiencies as high as 9.0%. This is due to enhanced electrons more efficiently at the CH3NH3PbI3 /compact-TiOx interface from the C60 leading to improved photocurrent densities and fill factors.

Planar heterojunction perovskite solar cells fabricated by wet process

Organic-inorganic hybrid perovskite materials have been recently emerged as a promising cost- and energy efficient light absorber material for photovoltaic applications. Unfortunately, perovskite solar cells have a problem with decreacement of power conversion efficiency due to degradation in the air. To detect the reason of degradation on perovskite solar cells, we exposed deposited CH3NH3PbI3 and HC(NH2)2PbI3 films to the O2 or (H2O+N2) atmosphere condition. Analysis of the film revealed that the large energy band gap was shown due to influence of H2O molecule in CH3NH3PbI3 and HC(NH2)2PbI3. In (H2O+N2) atmosphere conditions, the existence of CH3NH3I and HC(NH2)2I molecule has found to affect the morphology, absorption and as well as crystalline diffraction peak. The resultant perovskite crystalline structure was degraded by H2O molecules in the air exposure condition.