Planar CH3NH3PbI3 Perovskite Solar Cells Research Articles

Influence of Charge Transport Layers on Capacitance Measured in Halide Perovskite Solar Cells

Summary Capacitance-based techniques have been used to measure the electrical properties of halide perovskite solar cells (PSCs) such as defect activation energy and density, carrier concentration, and dielectric constant, which provide key information for evaluating the device performance. Here, we show that capacitance-based techniques cannot be used to reliably analyze the properties of defects in the perovskite layer or at its interface, because the high-frequency capacitance signature is due to the response of charge carriers in the hole-transport layer (HTL). For HTL-free PSCs, high-frequency capacitance can be considered as the geometric capacitance for analyzing the dielectric constant of the perovskite layer because there is no trapping and de-trapping of charge carriers in the perovskite layer. We further find that the low-frequency capacitance signature can be used to calculate the activation energy of the ionic conductivity of the perovskite layer, but the overlapping effects with charge transport materials must be avoided.

Study of inverted planar CH3NH3PbI3 perovskite solar cells fabricated under environmental conditions

Organic-inorganic inverted perovskite solar cells have been analyzed. This structure uses organic semiconductors as electron and hole selective electrodes and the perovskite as light harvesting layer. The anti-solvent deposition method is a frequently used techniques in the elaboration of conventional perovskite solar cells (FTO/TiO2/CH3NH3PbI3/Spiro-OMetad/Au). However, the anti-solvent method is seldom used in the inverted structure. In this work, we use the anti-solvent method to fabricate the perovskite film for solar cells in the ITO/PEDOT:PSS/CH3NH3PbI3/PC61BM/Ag configuration, systematically studying the effect of the anti-solvent dripping time and the relative humidity in cell fabrication and performance. The morphological, optical and photovoltaic analyses indicate that the right combination of these two parameters will result in a preferential crystal growth in the (1 1 0) orientation. This allows the formation of homogeneous pinhole-free films that enhance light harvesting and reduce charge-carrier leakage, hence increasing short circuit current and fill factor to obtain a photo-conversion efficiency of about ∼10%.

Photovoltaic performance of planar CH3NH3PbI3 perovskite solar cells based on CdS and high transmittance Cd(S,O) electron transport layers stacked with ZnO hole blocking layer

The chemical bath deposited n-type CdS and Cd(S,O) layer were implemented as electron transport (ET) layers integrated with ZnO hole blocking (HB) layer in the fabrication of planar CH3NH3PbI3 (MAPbI3) perovskite solar cells (PSC). The bonding environment and native defect structure of CdS and Cd(S,O) ET layers were established by Raman and photoluminescence spectral analysis. Optical studies showed that Cd(S,O) has higher UV–Vis transmittance and band edge threshold relative to CdS of similar thickness. The photovoltaic performance of the solar cells evaluated with CdS and Cd(S,O) ET layers of different 40-, 55-, and 80-nm thickness shows the effect of light intensity at the MAPbI3 photoabsorber and establishes the importance of native defects in electron extraction and transport in determining photoconversion efficiency (PCE). The effect of defect states in CdS and Cd(S,O) over corresponding J–V curves and fill factor of PSC device are described in terms of an energy band model. For 40-nm-thick Cd(S,O)/ZnO (ET/HB) layer, a PCE of 11.1% was achieved and compared with 9.18% for the CdS/ZnO (ET/HB) layer.

Aerosol assisted chemical vapour deposition of conformal ZnO compact layers for efficient electron transport in perovskite solar cells

Ultrathin and compact ZnO films were firstly deposited on textured fluorine-doped tin oxide (FTO) electrodes via aerosol assisted chemical vapour deposition (AACVD). Planar CH3NH3PbI3 perovskite solar cells (PSCs) were fabricated under ambient conditions and a best power conversion efficiency (PCE) of 11.75% was achieved.

Planar perovskite solar cells employing copper(I) thiocyanate/N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine bilayer structure as hole transport layers

Organic hole transport materials, such as N2,N2,N2′,N2′,N7,N7,N7′,N7′-octakis(4-methoxyphenyl)-9,9′-spirobi[9H-fluorene]-2,2′,7,7′-tetramine (Spiro-OMeTAD), are commonly used as the hole transport materials in efficient perovskite solar cells, but the chemical synthetic procedure may increase the cost of the photovoltaic devices. On the other hand, inorganic hole transport materials, such as copper(I) thiocyanate (CuSCN) or copper(I) iodide (CuI), have potential for the manufacture of efficient and low-cost perovskite solar cells, but the performance of these devices is still imperfect. In this study, we demonstrate the use of an inorganic CuSCN and organic N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) hybrid bilayer as an alternative hole transport layer for planar CH3NH3PbI3 perovskite solar cells. The electronic behavior of the bilayer and the performance of the corresponding devices were discussed. As a result, the power conversion efficiency (PCE) for the best cells at AM1.5G illumination with a shadow mask was 12.3%.

Scalable synthesis of Ti-doped MoO2 nanoparticle-hole-transporting-material with high moisture stability for CH3NH3PbI3 perovskite solar cells

Ti doped MoO2 nanoparticles with high BET surface area of 135m2/g were synthesized via scalable solvothermal cracking of polycrystalline MoO3 microparticles prepared by ultrasonic spray pyrolysis. The pristine MoO2 and Ti doped MoO2 nanoparticles showed metallic conductivity, whereas the MoO3 microparticles had semi-conducting behavior. In addition, the Ti doping in MoO2 nanoparticles formed stronger MoO bond than the pristine MoO2 and consequently exhibited improved stability against humidity. Accordingly, the p-i-n type planar CH3NH3PbI3 perovskite solar cells with Ti doped MoO2 inorganic hole transporting material showed 15.8% of power conversion efficiency at 1 Sun condition (100mW/cm2) and significantly improved humidity stability.

Device pre‐conditioning and steady‐state temperature dependence of CH3NH3PbI3 perovskite solar cells

AbstractThe recent rise in power conversion efficiencies reported for perovskite solar cells has been a remarkable development in photovoltaics research. It is now pressing that the technology transitions from a research phenomenon to a real‐world deployable device: this will require both robust methods for efficiency measurement, and accurate models for performance variation at different conditions. However, the generally slow response of perovskite solar cells to changes in voltage bias and irradiance, and the susceptibility of these cells to degradation, presents significant challenges. In this paper, we investigate current and voltage stabilisation of planar CH3NH3PbI3 perovskite solar cells and observe remarkably large variations in stabilisation time depending on exposure history. To address this, we demonstrate a dynamic approach that continues device pre‐conditioning until pre‐determined stability criteria are met. This approach is then employed to obtain measurements of short‐circuit current and open‐circuit voltage temperature coefficients under quasi‐steady‐state conditions for perovskite devices and a control monocrystalline silicon cell. The obtained open‐circuit voltage temperature coefficient for the perovskite is −2700 ppm/°C, which interestingly, is similar to typically reported values for crystalline silicon devices. It is shown that the implemented approach can successfully differentiate between transient responses to the onset of illumination and true temperature related changes. We also find new manifestations of the complex transient processes that occur in perovskite devices. These observations highlight the importance of sophisticated characterisation approaches for correct characterisation of the performance of perovskite solar cells. Copyright © 2016 John Wiley & Sons, Ltd.

Efficient inverted-type perovskite solar cells using UV-ozone treated MoOx and WOx as hole transporting layers

Inverted-type perovskite solar cells offer the potential of fabrication by low-temperature solution processing as an alternative to conventional-type perovskite solar cells. PEDOT:PSS is commonly used as the hole transport layer (HTL), but its acidic nature may damage the reliability and stability of the photovoltaic device. In this study, we demonstrate the use of MoOx and WOx HTLs as an alternative to PEDOT:PSS for planar CH3NH3PbI3 perovskite solar cells. Furthermore, the MoOx and WOx HTLs are treated using a UV-ozone treatment to improve the surface coverage of the perovskite layer. The resultant conversion efficiency (PCE) for the best cells at AM1.5G illumination with a shadow mask was 13.1%.

Facile scalable synthesis of MoO2 nanoparticles by new solvothermal cracking process and their application to hole transporting layer for CH3NH3PbI3 planar perovskite solar cells

∼10nm sized MoO2 nanoparticles with high BET surface area of 170.14m2/g were synthesized via scalable new process of combining the ultrasonic spray pyrolysis and solvothermal cracking process. Initially, we synthesized polycrystalline MoO3 microparticles by the ultrasonic spray pyrolysis at 500°C or 600°C. Then the MoO3 microparticles were disassembled into crystalline grains and the grains were subsequently shattered to small MoO2 nanoparticles through the solvothermal polyol reduction process because the polycrystalline MoO3 microparticles are disassembled by thermal expansion and the crystalline MoO3 grains are shattered by volume shrinkage due to phase transition from MoO3 to MoO2. Finally, we applied the MoO2 nanoparticles/toluene solution to new inorganic hole transporting material for planar CH3NH3PbI3 perovskite solar cells. The planar type CH3NH3PbI3 perovskite solar cells exhibited stable efficiency of 14.8% for forward scan condition and 15.5% for reverse scan condition under illumination of 1 Sun (100mW/cm2).

Fatigue behavior of planar CH3NH3PbI3 perovskite solar cells revealed by light on/off diurnal cycling

Long-term stability represents a major challenge for the commercial deployment of hybrid perovskite solar cells (PSCs). The stability of solar cells is commonly tested under continuous illumination over extended periods of time, for example, 1000h. We have found that such a method does not adequately reflect the long-term performance of perovskite solar cells under the diurnal solar irradiation cycles experienced in real-world applications. We report a new characterization protocol of multiple 12-h cycles of darkness and illumination, uncovering a unique ‘fatigue’ behavior of PSCs. The PSC efficiency was found to decrease to 50% or less of its maximum value after storage in the dark for 12h under open circuit conditions. The solar cell performance was capable of recovering to its maximum value in the subsequent 12-h illumination period, but the recovery rate slowed significantly with successive illumination/darkness cycles. This fatigue mechanism was strongly dependent on the cell temperature. The identification of this fatigue behavior renders our proposed characterization protocol an essential component of perovskite solar cell testing.

Null current hysteresis for acetylacetonate electron extraction layer in perovskite solar cells.

Solution processed zirconium acetylacetonate (Zr(acac)) is successfully employed as an electron extraction layer, replacing conventional titanium oxide, in planar CH3NH3PbI3 perovskite solar cells. The as-prepared Zr(acac) film possesses high transparency, high conductivity, a smooth morphology, high wettability, compatibility with PbI2 DMF solution, and an energy level matching that of CH3NH3PbI3 perovskite material. An average power conversion efficiency of about 11.93%, along with a high fill factor of 74.36%, an open circuit voltage of 1.03 V, and a short-circuit current density of 15.58 mA cm(-2) is achieved. The overall performance of the devices is slight better than that of cells using ruthenium acetylacetonate (Ru(acac)). The differences between solar cells with different electron extraction layers in charge recombination, charge transport and transfer and lifetime are further explored and it is demonstrate that Zr(acac) is a more effective and promising electron extraction layer. This work provides a simple, and cost effective route for the preparation of an effective hole extraction layer.

Surface optimization to eliminate hysteresis for record efficiency planar perovskite solar cells

The efficiency of planar CH3NH3PbI3 perovskite solar cells has been improved up to 19.62% using an ionic liquid to modify the TiO2 electron transport layer, and the J–V hysteresis is completely eliminated.

Improving the Extraction of Photogenerated Electrons with SnO2 Nanocolloids for Efficient Planar Perovskite Solar Cells

Great attention to cost‐effective high‐efficiency solar power conversion of trihalide perovskite solar cells (PSCs) has been hovering at high levels in the recent 5 years. Among PSC devices, admittedly, TiO2 is the most widely used electron transport layer (ETL); however, its low mobility which is even less than that of CH3NH3PbI3 makes it not an ideal material. In principle, SnO2 with higher electron mobility can be regarded as a positive alternative. Herein, a SnO2 nanocolloid sol with ≈3 nm in size synthesized at 60 °C was spin‐coated onto the fuorine‐doped tin oxide (FTO) glass as the ETL of planar CH3NH3PbI3 perovskite solar cells. TiCl4 treatment of SnO2‐coated FTO is found to improve crystallization and increase the surface coverage of perovskites, which plays a pivotal role in improving the power conversion efficiency (PCE). In this report, a champion efficiency of 14.69% (Jsc = 21.19 mA cm−2, Voc = 1023 mV, and FF = 0.678) is obtained with a metal mask at one sun illumination (AM 1.5G, 100 mW cm−2). Compared to the typical TiO2, the SnO2 ETL efficiently facilitates the separation and transportation of photogenerated electrons/holes from the perovskite absorber, which results in a significant enhancement of photocurrent and PCE.

Planar CH3NH3PbI3 Perovskite Solar Cells with Constant 17.2% Average Power Conversion Efficiency Irrespective of the Scan Rate.

Planar CH3NH3PbI3 perovskite solar cells with constant 17.2% average power conversion efficiency irrespective of the scan rate are described. These properties are attributed to the formation of a pure CH3 NH3 PbI3 thin film by the introduction of a HI solution. Thereby, charge-injection/separation efficiency, charge-collection efficiency, diffusion coefficient, carrier lifetime, and traps are improved. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Lead-Halide Perovskite Solar Cells by CH3NH3I Dripping on PbI2-CH3NH3I-DMSO Precursor Layer for Planar and Porous Structures Using CuSCN Hole-Transporting Material.

The sequential fabrication scheme of the CH3NH3PbI3 layer has been improved to fabricate planar-structure CH3NH3PbI3 perovskite solar cells using CuSCN hole-transporting material (HTM). In the PbI2 layer fabricated by the spin-coating method, at first, small amounts of CH3NH3I (MAI) and DMSO were incorporated as the first-drip precursor layer on a flat TiO2 layer. On the first-drip precursor layers, an MAI solution was applied by either soaking (MAI-soaking method) or dripping using successive spin coating (MAI-dripping). The morphology and crystal transformations were observed by SEM and XRD, respectively. Using the normal sequential MAI-soaking method, we were unable to fabricate planar CH3NH3PbI3 perovskite solar cells with CuSCN HTM. Using the MAI-dripping method, however, a significant photovoltaic effect has been observed to be planar <TiO2/CH3NH3PbI3 perovskite/CuSCN> solar cells.