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

Enhanced Carrier Transport Distance in Colloidal PbS Quantum-Dot-Based Solar Cells Using ZnO Nanowires

Nanostructured solar cells are a promising area of research for the production of low cost devices that may eventually be capable of complementing or even replacing present technologies in the field of solar power generation. The use of quantum dots (QDs) in solar cells has evolved from being simple absorbers in dye-sensitized solar cells to sustaining the double functions of absorbers and carrier transporters in full solid state devices. In this work, we use both optical and electrical measurements to explore the diffusion limitations of carrier transport in cells made of a heterostructure combining lead sulfide (PbS) QDs as absorbers and hole carrier and zinc oxide nanowires as electron carrier material. The results show efficient charge collection along the PbS-QD/ZnO nanowire (NW) hybrid structure. This is because of the formation of band bending in the ZnO collector, allowing efficient charge separation and spatially well-separated carrier pathways, yielding a hole transportation of over 1 μm. We have also found a limitation in open-circuit voltage (Voc) associated with band bending in the ZnO collector.This research is supported by the Japan Science and Technology Agency (JST) thorough its “Funding Program for Core Research for Evolutional Science and Technology (339-5 CREST)” and New Energy and Industrial Technology Development Organization (0520002 NEDO) and the Ministry of Economy, Trade and Industry (METI), Japan. The work is also supported by Generalitat Valenciana (ISIC/2012/008 Institute of Nanotechnologies for Clean Energies, PROMETEO/2014/020). This work is partly supported by JX Nippon Oil & Energy Corporation. Cordial thanks are due to Toyo Corporation for the use of the ModuLab system (Solartron) for obtaining IMPS data

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

Temperature Effects on the Photovoltaic Performance of Planar Structure Perovskite Solar Cells

[EN] Temperature effects of CH3NH3PbI3 perovskite solar cells having simple planar architecture were investigated on the crystal structure and photovoltaic performance. The obvious changes in the CH3NH3PbI3 crystal structure were found by varying the temperature as a consequence to the augmentation in lattice parameters and expansion of the unit cell. The expansion of the crystal gave a serious influence on the performance of the solar cells, where the differences in the coefficients of the thermal expansion (CTEs) together with the lattice mismatch between TiO2 and perovskite materials might cause interfacial defects responsible for the deterioration in the photovoltaic performance. Interestingly, the hysteresis in the cubic phase is very small because of the less distorted angles of the CH3NH3PbI3 structure against the temperature fluctuation.The present work has been supported by New Energy and Industrial Technology Development Organization (NEDO, Japan) and Japan Society for the Promotion of Science (JSPS) for Overseas Researchers. The authors acknowledge Ajay Kumar Jena for his help.Cojocaru, L.; Uchida, S.; Sanehira, Y.; González-Pedro, V.; Bisquert, J.; Nakazald, J.; Kubo, T.... (2015). Temperature Effects on the Photovoltaic Performance of Planar Structure Perovskite Solar Cells. Chemistry Letters. 44(11):1557-1559. https://doi.org/10.1246/cl.150781S15571559441

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

Controlled Crystal Grain Growth in Mixed Cation–Halide Perovskite by Evaporated Solvent Vapor Recycling Method for High Efficiency Solar Cells

We developed a new and simple solvent vapor-assisted thermal annealing (VA) procedure which can reduce grain boundaries in a perovskite film for fabricating highly efficient perovskite solar cells (PSCs). By recycling of solvent molecules evaporated from an as-prepared perovskite film as a VA vapor source, named the pot-roast VA (PR-VA) method, finely controlled and reproducible device fabrication was achieved for formamidinium (FA) and methylammonium (MA) mixed cation–halide perovskite (FAPbI₃)_0.85(MAPbBr₃)_0.15. The mixed perovskite was crystallized on a low-temperature prepared brookite TiO₂ mesoporous scaffold. When exposed to very dilute solvent vapor, small grains in the perovskite film gradually unified into large grains, resulting in grain boundaries which were highly reduced and improvement of photovoltaic performance in PSC. PR-VA-treated large grain perovskite absorbers exhibited stable photocurrent–voltage performance with high fill factor and suppressed hysteresis, achieving the best conversion efficiency of 18.5% for a 5 × 5 mm² device and 15.2% for a 1.0 × 1.0 cm² device

A Switchable High-Sensitivity Photodetecting and Photovoltaic Device with Perovskite Absorber

Amplified photocurrent gain has been obtained by photodiodes of inorganic semiconductors such as GaAs and Si. The avalanche photodiode, developed for high-sensitivity photodetectors, requires an expensive vapor-phase epitaxy manufacture process and high driving voltage (50–150 V). Here, we show that a low-cost solution-processed device using a planar-structured ferroelectric organo-lead triiodide perovskite enables light detection in a large dynamic range of incident power (10^–7–10^–1 W cm^–2) by switching with small voltage (−0.9 to +0.5 V). The device achieves significantly high external quantum conversion efficiency (EQE) up to 2.4 × 10⁵% (gain value of 2400) under weak monochromatic light. On a single dual-functional device, incident small power (0.2–100 μW cm^–2) and medium to large power (>0.1 mW cm^–2) are captured by reverse bias and forward bias modes, respectively, with linear responsivity of current. For weak light detection, the device works with a high responsivity value up to 620 A W^–1

Lead-free perovskite solar cells using Sb and Bi-based A3B2X9 and A3BX6 crystals with normal and inverse cell structures

Abstract Research of CH3NH3PbI3 perovskite solar cells had significant attention as the candidate of new future energy. Due to the toxicity, however, lead (Pb) free photon harvesting layer should be discovered to replace the present CH3NH3PbI3 perovskite. In place of lead, we have tried antimony (Sb) and bismuth (Bi) with organic and metal monovalent cations (CH3NH3 +, Ag+ and Cu+). Therefore, in this work, lead-free photo-absorber layers of (CH3NH3)3Bi2I9, (CH3NH3)3Sb2I9, (CH3NH3)3SbBiI9, Ag3BiI6, Ag3BiI3(SCN)3 and Cu3BiI6 were processed by solution deposition way to be solar cells. About the structure of solar cells, we have compared the normal (n-i-p: TiO2-perovskite-spiro OMeTAD) and inverted (p-i-n: NiO-perovskite-PCBM) structures. The normal (n-i-p)-structured solar cells performed better conversion efficiencies, basically. But, these environmental friendly photon absorber layers showed the uneven surface morphology with a particular grow pattern depend on the substrate (TiO2 or NiO). We have considered that the unevenness of surface morphology can deteriorate the photovoltaic performance and can hinder future prospect of these lead-free photon harvesting layers. However, we found new interesting finding about the progress of devices by the interface of NiO/Sb3+ and TiO2/Cu3BiI6, which should be addressed in the future study

Enhanced Carrier Transport Distance in Colloidal PbS Quantum-Dot-Based Solar Cells Using ZnO Nanowires

Nanostructured solar cells are a promising area of research for the production of low cost devices that may eventually be capable of complementing or even replacing present technologies in the field of solar power generation. The use of quantum dots (QDs) in solar cells has evolved from being simple absorbers in dye-sensitized solar cells to sustaining the double functions of absorbers and carrier transporters in full solid state devices. In this work, we use both optical and electrical measurements to explore the diffusion limitations of carrier transport in cells made of a heterostructure combining lead sulfide (PbS) QDs as absorbers and hole carrier and zinc oxide nanowires as electron carrier material. The results show efficient charge collection along the PbS-QD/ZnO nanowire (NW) hybrid structure. This is because of the formation of band bending in the ZnO collector, allowing efficient charge separation and spatially well-separated carrier pathways, yielding a hole transportation of over 1 μm. We have also found a limitation in open-circuit voltage (<i>V</i>_oc) associated with band bending in the ZnO collector