MgO Nanoparticle Modified Anode for Highly Efficient SnO2-Based Planar Perovskite Solar Cells.
ABSTRACT: Reducing the energy loss and retarding the carrier recombination at the interface are crucial to improve the performance of the perovskite solar cell (PSCs). However, little is known about the recombination mechanism at the interface of anode and SnO2 electron transfer layer (ETL). In this work, an ultrathin wide bandgap dielectric MgO nanolayer is incorporated between SnO2:F (FTO) electrode and SnO2 ETL of planar PSCs, realizing enhanced electron transporting and hole blocking properties. With the use of this electrode modifier, a power conversion efficiency of 18.23% is demonstrated, an 11% increment compared with that without MgO modifier. These improvements are attributed to the better properties of MgO-modified FTO/SnO2 as compared to FTO/SnO2, such as smoother surface, less FTO surface defects due to MgO passivation, and suppressed electron-hole recombinations. Also, MgO nanolayer with lower valance band minimum level played a better role in hole blocking. When FTO is replaced with Sn-doped In2O3 (ITO), a higher power conversion efficiency of 18.82% is demonstrated. As a result, the device with the MgO hole-blocking layer exhibits a remarkable improvement of all J-V parameters. This work presents a new direction to improve the performance of the PSCs based on SnO2 ETL by transparent conductive electrode surface modification.
Project description:We report amorphous tin-indium-oxide (TIO, Sn fraction: >50 atomic percentage (at%)) thin films as a new electron transport layer (ETL) of perovskite solar cells (PSCs). TIO thin films with Sn fraction of 52, 77, 83, 92, and 100 at% were grown on crystalline indium-tin-oxide (ITO, Sn fraction: ~10 at%) thin films, a common transparent conducting oxide, by co-sputtering In<sub>2</sub>O<sub>3</sub> and SnO<sub>2</sub> at room temperature. The energy band structures of the amorphous TIO thin films were determined from the optical absorbance and the ultraviolet photoelectron spectra. All the examined compositions are characterized by a conduction band edge lying between that of ITO and that of perovskite (here, methylammonium lead triiodide), indicating that TIO is a potentially viable ETL of PSCs. The photovoltaic characteristics of the TIO-based PSCs were evaluated. Owing mainly to the highest fill factor and open circuit voltage, the optimal power conversion efficiency was obtained for the 77 at%-Sn TIO ETL with TiCl<sub>4</sub> treatment. The fill factor and the open circuit voltage changes with varying the Sn fraction, despite similar conduction band edges. We attribute these differences to the considerable changes in the electrical resistivity of the TIO ETL. This would have a significant effect on the shunt and/or the series resistances. The TIO ETL can be continuously grown on an ITO TCO in a chamber, as ITO and TIO are composed of identical elements, which would help to reduce production time and costs.
Project description:Incorporation of as prepared single-walled carbon nanotubes (SWCNTs) into the electron transporting layer (ETL) is an effective strategy to enhance the photovoltaic performance of perovskite solar cells (PSCs). However, the fundamental role of the SWCNT electrical types in the PSCs is not well understood. Herein, we prepared semiconducting (s-) and metallic (m-) SWCNT families and integrated them into TiO<sub>2</sub> photoelectrodes of the PSCs. Based on experimental and theoretical studies, we found that the electrical type of the nanotubes plays an important role in the devices. In particular, the mixture of s-SWCNTs and m-SWCNTs (2:1 w/w)-based PSCs exhibited a remarkable efficiency of up to 19.35%, which was significantly higher than that of the best control cell (17.04%). In this class of PSCs, semiconducting properties of s-SWCNTs play a critical role in extracting and transporting electrons, whereas m-SWCNTs provide high conductance throughout the electrode.
Project description:Efficient electron transport layer-free perovskite solar cells (ETL-free PSCs) with cost-effective and simplified design can greatly promote the large area flexible application of PSCs. However, the absence of ETL usually leads to the mismatched indium tin oxide (ITO)/perovskite interface energy levels, which limits charge transfer and collection, and results in severe energy loss and poor device performance. To address this, a polar nonconjugated small-molecule modifier is introduced to lower the work function of ITO and optimize interface energy level alignment by virtue of an inherent dipole, as verified by photoemission spectroscopy and Kelvin probe force microscopy measurements. The resultant barrier-free ITO/perovskite contact favors efficient charge transfer and suppresses nonradiative recombination, endowing the device with enhanced open circuit voltage, short circuit current density, and fill factor, simultaneously. Accordingly, power conversion efficiency increases greatly from 12.81% to a record breaking 20.55%, comparable to state-of-the-art PSCs with a sophisticated ETL. Also, the stability is enhanced with decreased hysteresis effect due to interface defect passivation and inhibited interface charge accumulation. This work facilitates the further development of highly efficient, flexible, and recyclable ETL-free PSCs with simplified design and low cost by interface electronic structure engineering through facile electrode modification.
Project description:In this study, a new, simple, and novel oblique electrostatic inkjet (OEI) technique is developed to deposit a titanium oxide (TiO2) compact layer (CL) on fluorine-doped tin oxide (FTO) substrate without the need for a vacuum environment for the first time. The TiO2 is used as electron transport layers (ETL) in planar perovskite solar cells (PSCs). This bottom-up OEI technique enables the control of the surface morphology and thickness of the TiO2 CL by simply manipulating the coating time. The OEI-fabricated TiO2 is characterized tested and the results are compared with that of TiO2 CLs produced by spin-coating and spray pyrolysis. The OEI-deposited TiO2 CL exhibits satisfactory surface coverage and smooth morphology, conducive for the ETLs in PSCs. The power-conversion efficiencies of PSCs with OEI-deposited TiO2 CL as the ETL were as high as 13.19%. Therefore, the present study provides an important advance in the effort to develop simple, low-cost, and easily scaled-up techniques. OEI may be a new candidate for depositing TiO2 CL ETLs for highly efficient planar PSCs, thus potentially contributing to future mass production.
Project description:Recently, reported perovskite solar cells (PSCs) with high power conversion efficiency (PCE) are mostly based on mesoporous structures containing mesoporous titanium oxide (TiO<sub>2</sub>) which is the main factor to reduce the overall hysteresis. However, existing fabrication approaches for mesoporous TiO<sub>2</sub> generally require a high-temperature annealing process. Moreover, there is still a long way to go for improvement in terms of increasing the electron conductivity and reducing the carrier recombination. Herein, a facile one-step, in situ, and low-temperature method was developed to prepare an Nb:TiO<sub>2</sub> compact-mesoporous layer which served as both scaffold and electron transport layer (ETL) for PSCs. The Nb:TiO<sub>2</sub> compact-mesoporous ETL-based PSCs exhibit suppressed hysteresis, which is attributed to the synergistic effect of the increased interface surface area caused by nano-pin morphology and the improved carrier transportation caused by Nb doping. Such a high-quality compact-mesoporous layer allows the PSCs assembled using optimized 2% Nb-doped TiO<sub>2</sub> to achieve a remarkable PCE of 19.74%. This work promises an effective approach for creating hysteresis-less and high-efficiency PSCs based on compact-mesoporous structures with lower energy consumption and cost.
Project description:Landmark power conversion efficiency (PCE) over 14% has been accomplished for single-junction polymer solar cells (PSCs). However, the inevitable fracture of inorganic transporting layers and deficient interlayer adhesion are critical challenges to achieving the goal of flexible PSCs. Here, a bendable and thickness-insensitive Al-doped ZnO (AZO) modified by polydopamine (PDA) has emerged as a promising electron transporting layer (ETL) in PSCs. It has special ductility and adhesion to the active layer for improving the mechanical durability of the device. Nonfullerenes PSCs based on PBDB-T-2F:IT-4F with AZO:1.5% PDA (80 nm) ETL yield the best PCE of 12.7%. More importantly, a prominent PCE, approaching 11.5%, is reached for the fully flexible device based on Ag-mesh flexible electrode, and the device retains >91% of its initial PCE after bending for 1500 cycles. Such thickness insensitivity, mechanical durability, and interfacial adhesion properties for the inorganic ETLs are desired for the development of flexible and wearable PSCs with reliable photovoltaic performance and large-area roll-to-roll printing manufacture.
Project description:The mesoporous TiO<sub>2</sub> nanoparticle-based scaffold structure is the best electron transport layer (ETL) for perovskite solar cells (PSCs) and is still used in most PSCs with optimal photovoltaic characteristics. However, the high sintering temperature of TiO<sub>2</sub> nanoparticles required to remove binders from the TiO<sub>2</sub> paste limits PSC application to flexible electronics. In this study, a simple interface modification process involving ethanol rinsing is developed to enhance the photovoltaic characteristics of low-temperature processed PSCs. This easy and fast technique could enable remarkable performance by PSCs by significantly increasing the fill factor and current density, leading to a power conversion efficiency more than four times that of untreated solar cells.
Project description:Low-work-function poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PSS) modified with polyethylenimine (PEIE) was used as an electron transport layer (ETL) for polymer solar cells (PSCs). A thin layer of PEIE film was spin-coated onto the surface on thePSS films, thus substantially changing their charge selectivity from supporting hole transport to supporting electron transport. It was also found that thePSS/PEIE ETL exhibited higher interfacial contact, a more favorable active morphology, and improved charge mobility. By virtue of these beneficial properties, inverted PSCs based on low-bandgap semiconducting photoactive layers achieved a notably improved power conversion efficiency (PCE) of 7.94%, superior even to the corresponding performance of devices with only a ZnO layer. Surpassing our expectations, compared with the extreme degradation of device stability observed when purePSS is used, PEIE-modifiedPSS can considerably suppress device degradation because of the hydrophobic and alkaline nature of PEIE, which not only reduces the hygroscopicity of thePSS but also neutralizes the acidicPSS and thus prevents the corrosion of the ITO cathode. These results demonstrate the potential of PEIE-modifiedPSS for use as an efficient ETL in commercial printed electronic devices.
Project description:Over the past five years, perovskite solar cells (PSCs) have gained intense worldwide attention in the photovoltaic community due to their low cost and high power conversion efficiencies (PCEs). One of the most significant issues in achieving high PCEs of PSCs is the development of suitable low-cost hole-transporting materials (HTMs). Here, we put forward a new concept of HTMs for PSCs: a 3D structure with a core of coplanar quinolizino acridine, derived from the conventional concept of 2D triphenylamine HTMs. A cheaper Ag nanolayer was utilized to replace Au as the counter electrodes, and the title HTM TDT-OMeTAD was synthesized via an easy four-step synthesis (total yield: 61%) to achieve the low cost and convenient manufacture of PSCs. Compared with the conventional 2D triphenylamine HTM, TTPA-OMeTPA, PSC devices based on the 3D HTM TDT-OMeTPA showed a significant improvement in PCE from 10.8% to 16.4%, even outperforming Spiro-OMeTAD (14.8%). TDT-OMeTAD's highest PCE mainly results from it having the highest open-circuit voltage (Voc) of 1.01 V in this work, which is proven to be due to the higher hole mobility, matching energy levels, higher hydrophobicity and the smaller dark current. Moreover, an incident photon-current conversion efficiency (IPCE) test and time-resolved photoluminescence (TRPL) have been carried out to observe the better hole injecting efficiency and photoelectric conversion capability of TDT-OMeTPA based PSCs than Spiro-OMeTAD. The TDT-OMeTPA based PSCs exhibited >75% reproducibility (PCE > 15%) and retained 93.2% of the initial PCE after >500 hours.
Project description:The possibility to manufacture perovskite solar cells (PSCs) at low temperatures paves the way to flexible and lightweight photovoltaic (PV) devices manufactured via high-throughput roll-to-roll processes. In order to achieve higher power conversion efficiencies, it is necessary to approach the radiative limit via suppression of non-radiative recombination losses. Herein, we performed a systematic voltage loss analysis for a typical low-temperature processed, flexible PSC in n-i-p configuration using vacuum deposited C60 as electron transport layer (ETL) and two-step hybrid vacuum-solution deposition for CH3NH3PbI3 perovskite absorber. We identified the ETL/absorber interface as a bottleneck in relation to non-radiative recombination losses, the quasi-Fermi level splitting (QFLS) decreases from ~1.23 eV for the bare absorber, just ~90 meV below the radiative limit, to ~1.10 eV when C60 is used as ETL. To effectively mitigate these voltage losses, we investigated different interfacial modifications via vacuum deposited interlayers (BCP, B4PyMPM, 3TPYMB, and LiF). An improvement in QFLS of ~30-40 meV is observed after interlayer deposition and confirmed by comparable improvements in the open-circuit voltage after implementation of these interfacial modifications in flexible PSCs. Further investigations on absorber/hole transport layer (HTL) interface point out the detrimental role of dopants in Spiro-OMeTAD film (widely employed HTL in the community) as recombination centers upon oxidation and light exposure.