TiO2 Electron Transport Layer Research Articles

TiO2 Electron Transport Layer with p–n Homojunctions for Efficient and Stable Perovskite Solar Cells

HighlightsDeveloping a universal strategy of the p–n homojunction engineering that could significantly boost electron mobility of electron transport layer (ETL) by two orders of magnitude.Proposing a new mechanism based on p–n homojunction to explain inhibited carrier loss at buried interface.Setting a new performance benchmark as high as 25.50% for planar perovskite solar cells employing TiO2 as ETLs.

Improved charge kinetics of BiVO4/MoS2 photoanode by an TiO2 electron transport layer for photocatalytic fuel cell photodegradation and electricity generation

The poor contact between the photocatalyst and the FTO substrate are the main factors lead to the low performance of photocatalytic fuel cell (PFC). Herein, a FTO pre-treated with a TiO2 electron transport layer was used as a substrate for the synthesis of the MoS2/BiVO4/pre-FTO photoanode. The proposed MBV-4/pre-FTO photoanode with its enhances the visible light absorption and effectively delays the recombination of the photoexcited charge. The MBV-4/pre-FTO composite photoanode (6.02 mA/cm2) exhibited a photocurrent density that was 2.2 times higher than that of the BiVO4 photoanode (2.78 mA/cm2). This is attributed to the short charge migration length of the thin MoS2 layer, the fast photoexcited electron transport effect of the TiO2 seed layer, and the heterojunction structure of the proposed photoanode. The DFT calculation result indicated that the TiO2 electron transport layer showed an outstanding photoelectron attractive and transporting effect. The MoS2/Ni foam was employed as the photocathode to establish a mismatched Fermi level for driving PFC. The short-circuit current, open-circuit voltage, and maximum power density of the PFC were 0.578 mA/cm2, 0.632 V, and 0.125 mW/cm2, respectively. The main photodegradation active species are the superoxide anion (∙O2–) and the photoexcited hole (h+), and the degradation efficiency is 61.97 %.

Enhanced photovoltaic performance of dye sensitized solar cells using cesium bromide modified TiO2 electron transport layer

TiO2 is one of the most widely explored materials as an electron transport layer (ETL) in dye sensitized solar cells (DSSCs) due to its excellent physical and chemical properties. However, recombination at the device's interface slackens the charge carrier movement, adversely affecting their device performance. Rapid extraction of photogenerated charge carriers plays a vital role in developing high efficiency DSSCs. The conduction band alignment of TiO2 ETL and N719 dye light absorber plays a crucial role in charge carrier dynamics of DSSCs. Herein, the band structure of TiO2 ETL is finely tuned by the incorporation of cesium bromide (CsBr). At the optimal concentration (0.4 Wt. %), DSSCs achieved the best power conversion efficiency (PCE) of 9.28 % compared to 7.61 % for pristine TiO2. The modified TiO2–CsBr ETL induced a negative shift in flat band potential (Vfb) from −0.46 to −0.50 V, which improved the open circuit voltage (VOC), its work function (ɸ) from −4.71 to −3.75 eV and increased conduction band minimum (CBM) from −3.58 to −2.42 eV. CsBr incorporation increased electron density in TiO2 matrix, indicating the suppression of trap state and significantly improved the overall photovoltaic performance of DSSCs.

Tailoring interface and morphology of TiO2 electron transport layer with potassium bitartrate for high-performance perovskite solar cells

The performance of perovskite solar cells (PSCs) has rapidly improved, largely due to advancements in mitigating inherent defects and enhancing interface carrier transport properties. Herein, we provide a facile method to improve the morphology of TiO2 ETLs, suppress defects at interface, and tailor energy level alignment to enhance carrier separation and extraction efficiency by introducing potassium bitartrate (KBT) into the TiO2 electron transport layers (ETLs), achieving high-efficiency and stable PSCs. KBT molecules can enhance the surface smoothness of TiO2 ETLs, resulting in denser and more uniform perovskite films. In addition, the carboxyl groups, hydroxyl groups, and potassium cations containing in KBT improve charge transport efficiency at TiO2/perovskite interface by reducing non-radiative recombination centers in TiO2 and perovskite bottom as well as improving energy level matching. As a result, the target PSC exhibits an obvious improvement in performance with a champion efficiency of 23.35 %, which is greatly improved relative to the control (21.66 %). The long-term operational stability is also remarkably enhanced, after 800 h MPPT, PSCs with KBT remain over 80 % of its initial efficiency. PSCs with KBT-doped ETLs exhibit increased efficiency and stability, highlighting potential of KBT as an interface engineering tool for enhancing PSCs performance.

Record-Efficiency Printable Hole-Conductor-Free Mesoscopic Perovskite Solar Cells Enabled by the Multifunctional Schiff Base Derivative.

Tailoring multifunctional additives for performing interfacial modifications, improving crystallization, and passivating defects is instrumental for the fabrication of efficient and stable perovskite solar cells (PSCs). Here, a Schiff base derivative, (chloromethylene) dimethyliminium chloride (CDCl), is introduced as an additive to modify the interface between the mesoporous TiO2 electron transport layer and the MAPbI3 light absorber during the annealing process. CDCl chemically links to TiO2 and MAPbI3 through coordination and hydrogen bonding, respectively, and results in the construction of fast electron extraction channels. CDCl also optimizes the energy-level alignment of the TiO2/MAPbI3 heterojunction and improves the pore-filling and crystallization of MAPbI3 in the mesoscopic scaffold, which inhibits nonradiative recombination and eliminates open-circuit voltage losses. As a result, an impressive power conversion efficiency of 19.74%, which is the best one ever reported, is obtained for printable carbon-based hole-conductor-free PSCs based on MAPbI3.

Bottom-up multi-interface modification boosts the performance of carbon-based HTL-free all-inorganic CsPbI2Br perovskite solar cells

The inferior interface quality between CsPbI2Br perovskite and the electron transport layer (ETL) as well as carbon electrode limits the stability and power conversion efficiency (PCE) of hole transport layer (HTL) free carbon-based all-inorganic CsPbI2Br perovskite solar cells (C-IPSCs). Herein, perfluoropropionic acid (PFPA) is designed as a bottom-up multiple surface defect passivator that can simultaneously passivate perovskite/TiO2 interface and perovskite/carbon electrode interface. The comprehensive experiments demonstrate that PFPA can not only optimize the electron mobility, conductivity, and band structure of the TiO2 ETL through passivating oxygen vacancies (VO), but also diffuse to the upper surface of perovskite film through grain boundaries to passivate the surface lead defects, thereby facilitating the gradient alignment of the perovskite surface energy levels with the carbon electrode. At the same time, PFPA can effectively release the tensile stress at the interface of perovskite and reduce the delocalization state of the band tail caused by lattice distortion, so as to prepare high-quality perovskite films. As a result of the above interaction, the PCE of HTL-free CsPbI2Br C-IPSCs after PFPA modification is increased from 12.24% (control device) to 14.15%. In addition, the modified unencapsulated devices show superior long-term stability and thermal stability.

Enhancing the stability and efficiency of carbon-based perovskite solar cell performance with ZrO2-decorated rGO nanosheets in a mesoporous TiO2 electron-transport layer.

Improving the role of electron-transport layers (ETLs) in carbon-based perovskite solar cells (CPSCs) is a promising method to increase their photovoltaic efficiency. Herein, we employed rGO sheets decorated with ZrO2 nanoparticles to increase the electron transport capability of mesoporous TiO2 ETLs. We found that the rGO/ZrO2 dopant enhanced the conductivity of the ETL, reducing the charge-transfer resistance at the ETL/perovskite interface and reducing charge recombination in the corresponding CPSCs. Notably, this dopant did not effectively change the transparency of ETLs, while increasing the light-harvesting ability of their own top perovskite layer by improving the crystallinity of the perovskite layer. The rGO/ZrO2-containing ETLs produced a champion efficiency of 15.21%, while devices with a net ETL recorded a maximum efficiency of 11.88%. In addition, the modified devices showed a higher stability behavior against ambient air than the net devices, which was linked to the passivated grain boundaries of the modified perovskite layers along with the improved hydrophobicity.

Extending the Success of Halide Perovskites from Solar Cells to Photoelectrodes and Photocatalysts

Photoelectrochemical and photocatalytic conversion of water and carbon dioxide using solar energy offers a clean and sustainable solution to meet the world’s energy requirements. Achieving their full potential depends on developing inexpensive photoelectrodes and photocatalysts that can efficiently absorb solar light and drive photoinduced charges to react with water and carbon dioxide. In this talk, I will present the recent developments of our group in the preparation of inexpensive photoanodes and photocatalysts made of halide perovskites such as CsPbBr3. These materials are revolutionizing the photovoltaics field due to their high absorption coefficient and excellent optoelectronic properties, and now offer an opportunity to revolutionize photoelectrochemistry and photocatalysis if their instability in aqueous environments is addressed. We have found novel strategies to protect halide perovskites with printed carbon layers and graphite sheets functionalized with NiFeOOH water-oxidation electrocatalyst, achieving photoanodes with low onset potential (+0.4 VRHE) for solar water oxidation. We have also managed to boost charge separation in these photoanodes by engineering the CsPbBr3 phase to a 3D one that achieves enhanced energetics and better band alignment to the TiO2 electron transport layer and printed carbon electrode layer, achieving photocurrents around 8 mA cm-2 at 1.23 VRHE for water oxidation. Moreover, our carbon/graphite protection and NiFeOOH functionalization methods impart days of stability to the photoanodes, easily extended to weeks, compared with seconds in the absence of protection. Regarding photocatalysts made of halide perovskite, we have found novel approaches based on mechanochemical syntheses and antisolvent crystallization to prepare different composites of CsPbBr3 and other perovskites, including Cs2AgBiBr3/bismuthene and Cs3Bi2Br9/g-C3N4, all photocatalytically active in the reduction of CO2. An extended characterization allows us to relate their physical and charge-transfer properties to their performance, providing guidance in their rational design for their optimization and future application.

Optical and electrical characteristics of perovskite solar cells incorporating MoO3 as an active layer

Perovskite-based solar cell technologies have sparked much interest in recent decades. A solar cell’s efficiency is an essential factor in developing a highly efficient device. The power conversion efficiency (PCE) of Perovskite-based solar cells can be enhanced by adding new materials to the photon-absorbing layer and altering the electron and hole transport layers. Titanium dioxide (TiO2) is commonly used in electron transport layers (ETLs), but it has been shown that replacing TiO2 with molybdenum trioxide (MoO3) improves PCE. We use the OghmaNano software to simulate a perovskite-based solar cell and investigate the PCE for TiO2 and MoO3 ETL layers by altering their thickness. The influence of electron and hole drift diffusion, carrier continuity equations in the position space to describe charge flow within the device, Poisson’s equation, and charge carrier recombination have all been investigated in the context of solar cell simulation. It was observed that by substituting the ETL layer of TiO2 with MoO3 in the device, the PCE significantly increases.

Optimal TiO2 Nanoparticles Electron Transporting Layer for Highly Efficient Ambient-atmosphere Fabricated Carbon-based Perovskite Solar Cells

T he electron transporting layer (ETL) is a critical component for carbon-based planar Cs0.17FA0.83Pb(I0.83Br0.17)3 perovskite solar cells (C-PSCs), as it facilitates efficient charge transport between the perovskite material and the cathode. The low temperature processed TiO2 nanoparticles (TiO2 NPs) ETL (150°C) are widely employed in C-PSCs. However, the dispersion of commercial TiO2 NPs in colloid solution is often unstable, leading to particle agglomeration and sedimentation, which negatively affects the performance of C-PSCs. Therefore, it is crucial to achieve stable dispersion of TiO2 NPs in colloid solution before their application as ETL in C-PSCs. Furthermore, the surface properties of the TiO2 ETL such as the uniformity of film significantly impact the overall performance of C-PSCs. The objective of this study was to optimize the TiO2 ETL by investigating the dispersion of TiO2 NPs and varying their concentration in the solution for applying in ambient-atmosphere fabricated C-PSCs. The TiO2 NPs were dispersed in different solvents, including isopropanol, ethanol, and water. As a result, ethanol was the most effective solvent for dispersing TiO2 NPs, demonstrating the best dispersion stability. The concentration of TiO2 NPs in ethanol was then varied between 10-70 mg/ml. The results showed that the optimal concentration was 50 mg/ml, as it produced a high-quality ETL with a more uniform TiO2 film. This optimized TiO2 ETL in C-PSCs resulted in the highest power conversion efficiency (PCE) of 13.10% with FF, VOC, and JSC values of 65.50%, 1.02 V, and 19.52 mA/cm2, respectively.

Simultaneous Enhancement of Efficiency and Operational-Stability of Mesoscopic Perovskite Solar Cells via Interfacial Toughening.

The combined effects of compact TiO2 (c-TiO2 ) electron-transport layer (ETL) are investigated without and with mesoscopic TiO2 (m-TiO2 ) on top, and without and with an iodine-terminated silane self-assembled monolayer (SAM), on the mechanical behavior, opto-electronic properties, photovoltaic (PV) performance, and operational-stability of solar cells based on metal-halide perovskites (MHPs). The interfacial toughness increases almost threefold in going from c-TiO2 without SAM to m-TiO2 with SAM. This is attributed to the synergistic effect of the m-TiO2 /MHP nanocomposite at the interface and the enhanced adhesion afforded by the iodine-terminated silane SAM. The combination of m-TiO2 and SAM also offers a significant beneficial effect on the photocarriers extraction at the ETL/MHP interface, resulting in perovskite solar cells (PSCs) with power-conversion efficiency (PCE) of over 24% and 20% for 0.1 and 1cm2 active areas, respectively. These PSCs also have exceptionally long operational-stability lives: extrapolated T80 (duration at 80% initial PCE retained) is ≈18000 and 10000h for 0.1 and 1cm2 active areas, respectively. Postmortem characterization and analyses of the operational-stability-tested PSCs are performed to elucidate the possible mechanisms responsible for the long operational-stability.

Surface Energy Engineering of Buried Interface for Highly Stable Perovskite Solar Cells with Efficiency Over 25.

The abundant oxygen-related defects (e.g., O vacancies, O-H) in the TiO2 electron transport layer results in high surface energy, which is detrimental to effective carrier extraction and seriously impairs the photovoltaic performance and stability of perovskite solar cells. Here, novel surface energy engineering (SEE) is developed by applying a surfactant of heptadecafluorooctanesulfonate tetraethylammonium (HFSTA) on the surface of the TiO2 . Theoretical calculations show that the HFSTA-TiO2 is less prone to form O vacancies, leading to lower surface energy, thus improving the carrier-extraction efficiency. The experimental results show that superior perovskite film is obtained due to the reduced heterogeneous nucleation sites and improved crystallization process on the modified TiO2 . Furthermore, the flexible long alkyl chains in HFSTA considerably relieve the compressive stresses at the buried interface. By combining the passivation of TiO2 , crystallization process modulation, and stress relief, a champion PCE up to 25.03% is achieved. The device without encapsulation sustains 92.2% of its initial PCE after more than 2500h storage under air ambient with relative humidity of 25-30%. The SEE of a buried interface paves a new way toward high-efficiency, stable perovskite solar cells.

Improved performances in Sb2Se3 solar cells based on CdS buffered TiO2 electron transport layer

Improved performances in Sb2Se3 solar cells based on CdS buffered TiO2 electron transport layer

Preliminary exploration of the influence of N+/NHx+ ions/groups bombardment at TiO2 ETLs on performance of MAPbI3 perovskite solar cells

The service stability of organic–inorganic hybrid metal halide perovskite solar cells (PSCs) is one of most important factors, which is seriously influenced by the decomposition of perovskite layer. Especially, the decomposition of perovskite layer could deteriorate the interface between perovskite layer and TiO2 electron transport layer (ETL). In this work, TiO2 ETLs are prepared by the sputtering technique and traditional spin-coating technique. Then, TiO2 ETLs are bombarded by N+/NHx+ ions/groups. PSCs with all TiO2 ETLs are prepared and measured. The results show that after bombardment, N+/NHx+ ions/groups could chemically react with Ti/O ions at surface of TiO2 ETLs. As a result, the conduction band minimum and transfer resistance of TiO2 ETLs both deteriorate, which decrease the power conversion efficiency of PSCs seriously. While, because anatase TiO2 (001) crystal face consists of saturated O/Ti ions and displays the highest surface free energy, TiO2 ETLs with anatase (001) preferred orientation displays the optimal restraint on deterioration of power conversion efficiency caused by N+/NHx+ ions/groups bombardment. Based on above results, TiO2 ETLs with anatase (001) preferred orientation should be the optimal one for PSCs, which could improve the service stability obviously.

Effect of addition of indium oxide layer on all-inorganic perovskite solar cells

In perovskite solar cells, the interface plays a crucial role in photovoltaic performance because excitons dissociate and compound at the interface. In this paper, the optical absorption layer of In2O3 planar perovskite solar cells is studied, which is an efficient intermediate layer between the TiO2 electron transport layer and perovskite. The modification of the In2O3 interlayer increases the average power conversion efficiency from 6.74% to 10.68%. Based on this background, some other feature descriptions are also carried out. The results show that the photovoltaic performance can be improved by depositing the In2O3 interlayer, mainly due to the improved film morphology, reduced recombination center, bulk carrier concentration and Hall mobility. It has been shown that In2O3 can be used as an efficient interface material on all-inorganic perovskite solar cells.

Low-cost lead-free perovskite solar cell with graphene oxide as hole transport layer and carbon as back contact

In this work, an innovative design for environmentally benign perovskite solar cells (PSCs) is introduced by incorporating graphene oxide (GO) as the hole transport layer (HTL) and utilizing carbon for the back contact. Eschewing the traditionally used CH3NH3PbI3, which raises environmental concerns due to lead content, the proposed design features the eco-friendly CH3NH3SnI3 as the absorber layer. The strategic inclusion of GO as the HTL amplifies the PSC's operational efficiency, owing to its superior exciton dissociation and charge transport properties, while simultaneously offering an economical fabrication strategy. Together with the carbon back contact, this configuration promises a sustainable and cost-efficient PSC solution. The proposed PSC architecture comprises FTO (window layer)/TiO2 (electron transport layer)/CH3NH3SnI3 (absorber layer)/GO (HTL)/C (back contact). Through rigorous optimization processes – encompassing parameters like layer thicknesses, interfacial defects, and doping levels – a commendable enhancement in PSC's performance metrics is achieved. The resultant design registered a power conversion efficiency (PCE) of 21.40% and a fill factor (FF) of 83.98%. Furthermore, thermal evaluation from 300 K to 400 K revealed the PSC's exceptional thermal resilience, underscoring its suitability for commercial deployment. All simulations and analyses are conducted using the SCAPS-1D software.

Recent Advances of Doped SnO2 as Electron Transport Layer for High-Performance Perovskite Solar Cells.

Perovskite solar cells (PSCs) have garnered considerable attention over the past decade owing to their low cost and proven high power conversion efficiency of over 25%. In the planar heterojunction PSC structure, tin oxide was utilized as a substitute material for the TiO2 electron transport layer (ETL) owing to its similar physical properties and high mobility, which is suitable for electron mining. Nevertheless, the defects and morphology significantly changed the performance of SnO2 according to the different deposition techniques, resulting in the poor performance of PSCs. In this review, we provide a comprehensive insight into the factors that specifically influence the ETL in PSC. The properties of the SnO2 materials are briefly introduced. In particular, the general operating principles, as well as the suitability level of doping in SnO2, are elucidated along with the details of the obtained results. Subsequently, the potential for doping is evaluated from the obtained results to achieve better results in PSCs. This review aims to provide a systematic and comprehensive understanding of the effects of different types of doping on the performance of ETL SnO2 and potentially instigate further development of PSCs with an extension to SnO2-based PSCs.

Low-temperature preparation of titanium dioxide thin layer for highly efficient CsPbI3 perovskite solar cells

All-inorganic CsPbI3 perovskite solar cells (PSCs) are the focus of the photovoltaic field due to their great thermal stability and potential in tandem devices. However, the common titanium dioxide (TiO2) electron transport layer (ETL) is manufactured at high temperature and is challenging to regulate the thickness. Here, we propose a unique strategy to fabricate thin TiO2 at low temperatures using atomic layer deposition (ALD) and a low-concentration Titanium tetrachloride/isopropanol (TiCl4/IPA) solution method. The ultra-thin compact ALD-TiO2 (A-TiO2) is employed to minimize the leakage channels and suppress the recombination rate at the tips of rough fluorine-doped tin oxide (FTO) substrates. Subsequently, the solution-TiO2 (S–TiO2) regulates the work function to improve the energy level alignment. The A-TiO2/S–TiO2 composite facilitates carrier charge extraction and transport at the interface between ETL and perovskite layer. As a result, the device-based A-TiO2/S–TiO2 ETL delivers a champion efficiency of 19.6% and outstanding stability under continuous illumination in ambient air. This study demonstrates a simple and cost-effective method for fabricating CsPbI3 PSC and promoting their potential for commercialization.

One‐Step Construction of a Perovskite/TiO2 Heterojunction toward Highly Stable Inverted All‐Layer‐Inorganic CsPbI2Br Perovskite Solar Cells with 17.1% Efficiency

AbstractAll‐layer‐inorganic perovskite solar cells (PSCs) are prized for their remarkable thermal stability and low cost. However, “imperfect contact” at the perovskite heterojunction hinders charge transport and causes photochemical deterioration, restricting photovoltaic performance, and operational stability. Herein, an efficient perovskite/TiO2 heterojunction is constructed, produced by adding TiO2 to an antisolvent to concurrently form a CsPbI2Br perovskite layer and a top TiO2 electron transport layer in one step, which significantly improves the interfacial contact and thus facilitates charge transport at the heterojunction. The resultant inverted all‐layer‐inorganic PSCs exhibit a superior efficiency of 17.1%. Moreover, given the high‐quality perovskite/TiO2 heterojunction and low interface defects, the encapsulated PSCs retain 91% or 92% of their initial efficiency for 1000 h under maximum power point tracking or damp‐heat conditions (85 °C and 85% relative humidity), respectively. Surprisingly, the unencapsulated PSCs maintain an initial efficiency of 86% during aging, even at 200 °C for 200 h.

C60-CN: A bifunctional interface modification material for perovskite solar cells

Titanium dioxide (TiO2) is regularly used as an electron transport material in n-i-p perovskite solar cells (PSCs). However, massive defects exist on the TiO2 surface, which will lead to serious hysteresis and interface charge recombination of the device, thus affecting the device’s efficiency. In this study, a cyano fullerene pyrrolidine derivative (C60-CN) was synthesized and applied to PSCs for the first time to modify the TiO2 electron transport layer. Systematic studies have shown that the addition of the C60-CN modification layer on the TiO2 surface will enlargement the perovskite grain size, improve the perovskite film quality, enhance electron transport, and reduce charge recombination. The C60-CN layer can significantly reduce the density of trap states in the perovskite solar cells. As a result, the PSCs based on C60-CN/TiO2 obtained a power conversion efficiency (PCE) of 18.60%, suppressing the hysteresis and improving the stability, whereas the PCE of the control device using the original TiO2 ETL was lower, 17.19%.