We used a two-step process to fabricate planar perovskite solar cells (PSCs) in which CH3NH3I (MAI) molecules intercalated into a PbI2 film. The crystal growth of PbI2 is particularly important to ...achieve perovskite films with high PSC performance. Herein, we attempted to control the crystal growth of PbI2 films through a simple spin-coating method at annealing temperatures of 70, 150, 250, and 350 °C and times of 1, 5, 10, and 30 min. We investigate the effects of the high-crystallite host PbI2 film on the crystallinity, film quality, and absorption of the resulting MAPbI3 perovskite film as well as the resulting performance of the planar PSCs. Under the optimal annealing conditions, a highly crystalline PbI2 film was reproducibly achieved at 250 °C for 30 min. Precise intercalation of MAI molecules into the PbI2 film contributed to a smooth perovskite film and good PSC performance. This work develops a fundamental understanding of the thermally induced controlled crystal growth of the parent PbI2 film, which influenced the bridging and intercalation with MAI, resulting in a high-quality perovskite film. This study will guide further development based on two-step processes of perovskite films that have optimal crystallinities and morphologies that contribute to high PSC performance.
The insufficient stability of CH3NH3PbI3 (MAPbI3)-based perovskite solar cells (PSCs) remains a significant concern in this field of research, so a device engineering approach is required to obtain ...efficient, stable PSCs. The present work used a sequential deposition process to alternately fabricate thin MAPbI3-based perovskite and cesium iodide (CsI) layers with precise control over the CsI intercalation, producing high quality cesium containing perovskite films. The optimal CsI film thickness when applied to either the up, down or both layers of the MAPbI3 perovskite film was also assessed. Interestingly, the application of a double layer CsI layer greatly altered the perovskite morphology to produce large grain sizes, as a result of the precise intercalation of the CsI molecules into the host MAPbI3. Furthermore, PSCs made with double layer CsI intercalation exhibited power conversion efficiencies as high as 18.43%. These exceeded the values obtained from devices made with pristine MAPbI3, or with CsI intercalation on either the bottom or top of the perovskite (16.14%, 17.92% and 17.26%, respectively). A double layer CsI intercalation device was stored in the dark at relative humidities of 40–50% for more than 4000 h and retained over 83% of its initial efficiency.
Sequential deposition technique was used to alternately fabricate CH3NH3PbI3 (MAPbI3) and cesium iodide (CsI) thin layers with precise control over the CsI intercalation, producing large grain size, and high-quality cesium containing perovskite films. When the CsI double-layer intercalate into the MAPbI3 framework effectively improves the efficiency and long-term stability of the perovskite solar cells. Display omitted
•Double layer CsI intercalation greatly altered the perovskite morphology.•The optimal CsI film thickness when applied to either the up, down or double layers of the MAPbI3 film were assessed.•Double layer CsI intercalation significantly improve the long-term stability of perovskite solar cells.
Hybrid organometal halide perovskites such as methylammonium lead iodide (MAPbI
3
) are a promising class of cost- and energy-efficient light absorption materials for thin-film photovoltaics. In this ...work, the preparation and characterization of MAPbI
3
nanoparticles (NPs) on TiO
x
/indium tin oxide glass substrates using a simple spin-coating technique have been investigated. The NPs were prepared by spin-coating solutions of MAPbI
3
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 MAPbI
3
NPs with an average diameter of 540 nm were homogeneously distributed on the TiO
x
substrates. MAPbI
3
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 MAPbI
3
. Therefore, the presence of an IL resulted in uniform thin films with good morphology.
In photovoltaic cells, increasing the light absorption coefficient enhances the photocurrent and quantum efficiency of the cell. Here, we report an efficient approach that enhances light absorption ...by changing the crystal phase of an evaporated ZnPc film on indium tin oxide (ITO) substrates. Under thermal treatment (>200 °C), the crystal phase of ZnPc changed from metastable α-ZnPc to stable β-ZnPc. We tested and compared the effects of this phase transition on the donor film of organic photovoltaic (OPV) cells. After treating the β-ZnPc film at 220 °C, the short-circuit current of the OPV was improved from 2.58 to 3.40 mA/cm2, and the quantum efficiency was improved from 650 to 750 nm. Moreover, on a copper iodide (CuI)–ITO substrate, the ZnPc molecules were precisely controlled in the lying-down orientation. With their lying-down orientations, the light absorbance capacities of the metastable α-ZnPc phase and stable β-ZnPc phase (annealed at 300 °C) were 1.3- and 1.5-fold higher, respectively, than that of metastable α-ZnPc standing upright on the ITO substrate. This work provides a fundamental understanding of the crystal phases and orientation changes of the ZnPc molecules, enabling maximization of the light absorption coefficient and the design of efficient small-molecule OPV cells.
In the blended solid of poly(3-hexylthiophene-2,5-diyl) (P3HT) and porphyrin (TPP)/TiO2 p-n hetero-junction solar cells, a photo-induced charge transfer between P3HT and TPP accelerated the charge ...separation in the depletion layer formed at the P3HT+TPP/TiO2 interface, enhancing the photovoltaic properties. For the blended cell containing zinc porphyrin as TPP, the energy conversion yield of 0DDT26% was obtained under the illumination of solar simulated light AM1DDT5-100mW/cm2.
Herein, we report an efficient approach to control the crystalline polymorph of evaporated α-sexithiophene (6T) thin films by keeping them overnight (12 h) under vacuum. Further, we investigated the ...effects on the performance of organic photovoltaic devices of controlling the 6T polymorph via this vacuum technique so that the films take on the low-temperature (LT) polymorph (in which the backbones of the 6T molecules lie flatter on the substratethe so-called “lying-down” orientation). Our results revealed that when the organic layer was deposited directly onto a copper(I) iodide interlayer, the angle between the organic backbone and the substrate was reduced in the LT polymorph compared with the high-temperature (HT) polymorph. The power conversion efficiency of solar cells could thus be enhanced from 0.58 to 1.77% via a change in the crystal polymorph of the 6T layer from HT to LT by simply keeping the films in vacuum for 12 h.
In a glass–indium tin oxide (ITO)/amine/regioregular poly(3-hexylthiophene) (P3HT):6,6-phenyl C61 butyric acid methyl ester (PCBM)/poly(3,4-ethylenedioxylenethiophene):poly(4-styrene sulfonic acid) ...(PEDOT:PSS)/Au cell, which uses small molecule amine-modified ITO as the electron collection electrode, a light-soaking effect under irradiation of simulated sunlight was restrained considerably compared with in an ITO/P3HT:PCBM/PEDOT:PSS/Au cell containing bare ITO. That is, the time taken to arrive at a saturated Voc from the initial Voc became short when the ionization potential (IP) of ITO reduced by the amine modification, and consequently both of its saturated Voc and power conversion efficiency (PCE) improved. The IP decreased with an increase in the number (N) of amino groups in a single amine molecule, because the basic amino groups can efficiently neutralize any acidic hydroxyl groups on ITO through a multipoint interaction. The superior performance of the cell containing the amine-modified electrode with large N was perhaps because the energy mismatch formed by a contact between ITO and acceptor PCBM reduced, and consequently the rate of electron collection at ITO increased.
•Surface-modification of ITO electrode with low molecular weight amines•Ionization potential of ITO was decreased by forming an electrical double layer.•Light-soaking effect has been observed by irradiating white light.•The light-soaking effect mainly improved the open-circuit photovoltage.•Open-circuit photovoltage was limited by ionization potential of amine-modified ITO.
A precise control of the morphology and crystallization of perovskite thin-films is well-correlated to higher perovskite solar cells performances. Ionic liquids (ILs) can retard perovskite ...crystallization to aid the formation of films with uniform morphology to realize highly efficient perovskite solar cells. Herein, we attempt to control the nanostructural growth of CH3NH3PbI3 thin films by adding ILs to the perovskite spin-coating solution and investigate the effect of IL viscosity on the resulting CH3NH3PbI3 nanoparticle (NP) thin films. NPs with desirable morphology were obtained using ILs with a low viscosity that completely dissolved in the CH3NH3PbI3 solution. In particular, the IL tetrabutylammonium chloride yielded NPs with a diameter of 500 nm and controllable morphology, crystallinity, and absorption behavior, which led to improved photovoltaic performance compared with that of solar cells containing NPs produced using other ILs. Our findings revealed a pathway to obtain uniformly distributed CH3NH3PbI3 NP thin films for use in perovskite solar cells. The developed method is well suited for large-scale production of perovskite thin films on flexible substrates.
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•Solutions of CH3NH3PbI3 and an ionic liquid (IL) were spin-coated to form nano-structure control thin films morphology.•The effects of IL viscosity on CH3NH3PbI3 film formation were investigated.•Tetrabutylammonium chloride gave films with controlled morphology and crystallinity.•The photovoltaic performance of the CH3NH3PbI3 thin films depended on IL viscosity.
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