Halide Perovskites for Indoor Photovoltaics: The Next Possibility

Halide Perovskites for Indoor Photovoltaics: The Next Possibilit

Impacts of Heterogeneous TiO₂ and Al₂O₃ Composite Mesoporous Scaffold on Formamidinium Lead Trihalide Perovskite Solar Cells

Heterogeneous TiO₂ and Al₂O₃ composites were employed as a mesoporous scaffold in formamidinium lead trihalide (FAPbI_3–<i>x</i>Cl_<i>x</i>)-based perovskite solar cells to modify surface properties of a mesoporous layer. It was found that the quality and morphology of the perovskite film were strongly affected by the TiO₂/Al₂O₃ ratio in the mesoporous film. The conversion efficiency of the perovskite solar cell was improved by using a composite of TiO₂ and Al₂O₃ in comparison with TiO₂- and Al₂O₃-based cells, yielding 11.0% for a cell with a 7:3 TiO₂/Al₂O₃ composite. Our investigation shows a change of electron transport path depending on a composition ratio of insulating Al₂O₃ to n-type semiconducting TiO₂ in a mesoporous layer

Efficiency Enhancement of ZnO-Based Dye-Sensitized Solar Cells by Low-Temperature TiCl₄ Treatment and Dye Optimization

ZnO is a promising candidate as a low-cost porous semiconductor material for photoelectrodes in dye-sensitized solar cells (DSSCs). However, ZnO-based DSSCs tend to exhibit lower energy conversion efficiencies than do those based on TiO₂. In this study, the performance of ZnO porous electrodes was enhanced using a surface treatment carried out by immersion in cold aqueous TiCl₄ solution that resulted in TiO₂-coated ZnO (<i>Z</i>/<i>T</i>) electrodes. The <i>Z</i>/<i>T</i> electrodes were sensitized with either the Ru complex dye N719 or the organic indoline dye D149. For each dye, the DSSCs with the <i>Z</i>/<i>T</i> photoelectrodes showed the highest open-circuit voltage (<i>V</i>_oc), short circuit current (<i>J</i>_sc), and power conversion efficiency compared to those with ZnO, TiO₂, or TiO₂-coated TiO₂ (<i>T</i>/<i>T</i>) electrodes. To study the effects of the TiCl₄ treatment, the relationships between the electron lifetime (τ), cell voltage, and electron density (<i>n</i>) of the cells prepared with each electrode, with each of the two dyes, or without either dye were assessed. It was found that the TiCl₄ treatment negatively shifted the conduction band edge (CBE) potential of the ZnO electrodes by more than 100 mV for both dyes and also in the absence of a dye. In addition, τ increased with the use of the organic D149 and in the absence of a dye. The DSSC with a D149-sensitized <i>Z</i>/<i>T</i> layer showed the highest efficiency of 4.89% under 100 mW cm^–2 irradiation

Severe Morphological Deformation of Spiro-OMeTAD in (CH₃NH₃)PbI₃ Solar Cells at High Temperature

The hole transport material, spiro-OMeTAD, in MAPbI₃ perovskite solar cells undergoes severe morphological deformation at high temperature, showing big voids in the layer when the devices are heated at 80 °C and above. It is puzzling that the voids emerge only in the area where the spiro-OMeTAD is capped with Au film and only in the case where the HTM contains both LiTFSI and TBP as additives

Effect of Electron Transporting Layer on Bismuth-Based Lead-Free Perovskite (CH₃NH₃)₃ Bi₂I₉ for Photovoltaic Applications

Methylammonium iodo bismuthate ((CH₃NH₃)₃Bi₂I₉) (MBI) perovskite is a promising alternative to rapidly progressing hybrid organic–inorganic lead perovskites because of its better stability and low toxicity compared to lead-based perovskites. Solution-processed perovskite fabricated by single-step spin-coating and subsequent heating produced polycrystalline films of hybrid perovskite (CH₃NH₃)₃Bi₂I₉), whose morphology was influenced drastically by the nature of substrates. The optical measurements showed a strong absorption band around 500 nm. The devices made on anatase TiO₂ mesoporous layer showed good performance with current density over 0.8 mA cm^–2 while the devices on brookite TiO₂ layer and planar (free of porous layer) was inefficient. However, all the MBI devices were stable to ambient conditions for more than 10 weeks

Emergence of Hysteresis and Transient Ferroelectric Response in Organo-Lead Halide Perovskite Solar Cells

Although there has been rapid progress in the efficiency of perovskite-based solar cells, hysteresis in the current–voltage performance is not yet completely understood. Owing to its complex structure, it is not easy to attribute the hysteretic behavior to any one of different components, such as the bulk of the perovskite or different heterojunction interfaces. Among organo-lead halide perovskites, methylammonium lead iodide perovskite (CH₃NH₃PbI₃) is known to have a ferroelectric property. The present investigation reveals a strong correlation between transient ferroelectric polarization of CH₃NH₃PbI₃ induced by an external bias in the dark and hysteresis enhancement in photovoltaic characteristics. Our results demonstrate that the reverse bias poling (−0.3 to −1.1 V) of CH₃NH₃PbI₃ photovoltaic layers prior to the photocurrent–voltage measurement generates stronger hysteresis whose extent changes significantly by the cell architecture. The phenomenon is interpreted as the effect of remanent polarization in the perovskite film on the photocurrent, which is most enhanced in planar perovskite structures without mesoporous scaffolds

Amorphous Metal Oxide Blocking Layers for Highly Efficient Low-Temperature Brookite TiO₂‑Based Perovskite Solar Cells

A fully low-temperature-processed perovskite solar cell was fabricated with an ultrathin amorphous TiO_<i>x</i> hole-blocking layer in combination with brookite TiO₂ prepared at temperature <150 °C. Structured with TiO_<i>x</i>/brookite TiO₂ bilayer electron collector, the perovskite solar cells exhibit high efficiency up to 21.6% being supported by high open-circuit voltage and fill factor up to 1.18 V and 0.83, respectively. Compared to SnO_<i>x</i> hole-blocking layer, TiO_<i>x</i> has better electron band alignment with brookite TiO₂ and hence, results in higher efficiency

Solution-Processed Transparent Nickel-Mesh Counter Electrode with in-Situ Electrodeposited Platinum Nanoparticles for Full-Plastic Bifacial Dye-Sensitized Solar Cells

A new type of embedded metal-mesh transparent electrode (EMTE) with in-situ electrodeposited catalytic platinum nanoparticles (PtNPs) is developed as a high-performance counter electrode (CE) for lightweight flexible bifacial dye-sensitized solar cells (DSSCs). The thick but narrow nickel micromesh fully embedded in a plastic film provides superior electrical conductivity, optical transmittance, and mechanical stability to the novel electrode. PtNPs decorated selectively on the nickel micromesh surface provide catalytic function with minimum material cost and without interfering with optical transparency. Facile and fully solution-processed fabrication of the novel CE is demonstrated with potential for scalable and cost-effective production. Using this PtNP-decorated nickel EMTE as the CE and titanium foil as the photoanode, unifacial flexible DSSCs are fabricated with a power conversion efficiency (PCE) of 6.91%. By replacing the titanium foil with a transparent ITO-PEN photoanode, full-plastic bifacial DSSCs are fabricated and tested, demonstrating a remarkable PCE of 4.87% under rear-side illumination, which approaches 85% of the 5.67% PCE under front-side illumination, among the highest ratio in published results. These promising results reveal the enormous potential of this hybrid transparent CE in scalable production and commercialization of low-cost and efficient flexible DSSCs

Vapor Annealing Controlled Crystal Growth and Photovoltaic Performance of Bismuth Triiodide Embedded in Mesostructured Configurations

Low stability of organic–inorganic lead halide perovskite and toxicity of lead (Pb) still remain a concern. Therefore, there is a constant quest for alternative nontoxic and stable light-absorbing materials with promising optoelectronic properties. Herein, we report about nontoxic bismuth triiodide (BiI₃) photovoltaic device prepared using TiO₂ mesoporous film and spiro-OMeTAD as electron- and hole-transporting materials, respectively. Effect of annealing methods (e.g., thermal annealing (TA), solvent vapor annealing (SVA), and Petri dish covered recycled vapor annealing (PR-VA)) and different annealing temperatures (90, 120, 150, and 180 °C for PR-VA) on BiI₃ film morphology have been investigated. As found in the study, grain size increased and film uniformity improved as temperature was raised from 90 to 150 °C. The photovoltaic devices based on BiI₃ films processed at 150 °C with PR-VA treatment showed power conversion efficiency (PCE) of 0.5% with high reproducibility, which is, so far, the best PCE reported for BiI₃ photovoltaic device employing organic hole-transporting material (HTM), owing to the increase in grain size and uniform morphology of BiI₃ film. These devices showed stable performance even after 30 days of exposure to 50% relative humidity, and after 100 °C heat stress and 20 min light soaking test. More importantly, the study reveals many challenges and room (discussed in the details) for further development of the BiI₃ photovoltaic devices

The Interface between FTO and the TiO₂ Compact Layer Can Be One of the Origins to Hysteresis in Planar Heterojunction Perovskite Solar Cells

Organometal halide perovskite solar cells have shown rapid rise in power conversion efficiency, and therefore, they have gained enormous attention in the past few years. However, hysteretic photovoltaic characteristics, found in these solid-state devices, have been a major problem. Although it is being proposed that the ferroelectric property of perovskite causes hysteresis in the device, we observed hysteresis in a device made of nonferroelectric PbI₂ as a light absorber. This result evidently supports the fact that ferroelectric property cannot be the sole reason for hysteresis. The present study investigates the roles of some key interfaces in a planar heterojunction perovskite (CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i>) solar cell that can potentially cause hysteresis. The results confirm that the interface between fluorine doped tin oxide (FTO) substrate and the TiO₂ compact layer has a definite contribution to hysteresis. Although this interface is one of the origins to hysteresis, we think that other interfaces, especially the interface of the TiO₂ compact layer with perovskite, can also play major roles. Nevertheless, the results indicate that hysteresis in such devices can be reduced/eliminated by changing the interlayer between FTO and perovskite