Enhancing photovoltaic performance of carbon-based perovskite solar cells by introducing plasmonic Au NPs

In recent years, perovskite solar cells have obtained a rapid development due to their large light absorption coefficient, low-cost and high power conversion efficiency (PCE). In this study, the one-dimensional ordered ZnO nanorod arrays were prepared on FTO glasses by chemical bath deposition at low temperature. TiO2 nanoparticles from different kinds of solution were further spin-coated onto the ZnO nano arrays to form ZnO/TiO2 composite nano arrays, as the electron transfer layer in perovskite solar cells. The microstructure of different ZnO/TiO2 composite nano arrays and their corresponding photovoltaic performance of the solar cells were investigated. It was found that the cells based on ZnO nano arrays treated by TiO2 nanoparticle paste exhibit the highest PCE. The influence of TiO2 paste concentration on the photovoltaic performance of cells was further investigated. It indicated that the cell achieves best photovoltaic performance at TiO2 paste concentration of 0.1 mol/L: open circuit voltage ( V oc) of 0.93 V, short circuit current ( J sc) of 15.30 mA cm−2, filling factor ( FF ) of 43% and PCE of 6.07%. The treatment of TiO2 paste on ZnO nano arrays results in perovskite nanoparticles can effectively fill into the cracks between ZnO nanorods and a flat and compact perovskite layer can also form on the top of ZnO nano arrays. These effectively enhance the loading of perovskite and suppress the recombination between carriers in cells, resulting in an improved photovoltaic performance. A further treatment of ZnO/TiO2 paste arrays with TiCl4 aqueous solution can significantly improve the photovoltaic performance of the perovskite solar cells: V oc=0.99 V, J sc=19.09 mA cm−2, FF =58%, and PCE of 11%. The TiCl4 treatment of ZnO/TiO2 composite arrays introduces small TiO2 nanoparticles (~3 nm) into nano arrays. The small nanoparticles can fully fill the cracks between the nanorods and create better contact between perovskite (both in top layer and the arrays) and nano arrays. The photo induced carrers can rapidly transfer via ZnO nanorods to the conductive substrates. Furthermore, the introduce of small TiO2 nanoparticles also increases the surface area of electrode to absorb more perovskite, and hence improve the adsorption of light and result in an improved photovoltaic performance of the cells.

Multi-functional L-histidine self-assembled monolayers on SnO2 electron transport layer to boost photovoltaic performance of perovskite solar cells

The functional material-based interface and additive engineering are considered as valid approaches to enhance the photovoltaic performance of perovskite solar cells (PSCs). However, most of these materials have been reported to play only one role in PSCs. Herein, we applied versatile potassium acetate (KAc) as the cathode buffer layer (CBL), electron transporting layer (ETL), and perovskite additive in all-inorganic CsPbI2Br PSCs, respectively. All the KAc-incorporated devices yield higher efficiency than the control device. Especially, we achieve the interfacial and doping synergistic effects by introducing KAc CBL between SnO2 ETL and CsPbI2Br perovskite. For the interfacial effect, the KAc CBL can passivate the Sn-related defects and optimize the interfacial energy-level alignment at the SnO2/CsPbI2Br contact. For the doping effect, KAc is partially doped into CsPbI2Br during spin-coating of the perovskite precursor solution due to its good solubility in the solvent of perovskite precursor, which results in the passivation of uncoordinated Pb2+ in the perovskite layer. Owing to the interfacial and doping synergistic effect, the power conversion efficiency (PCE) increases noticeably from 12.91% to 15.71% after inserting KAc CBL. Furthermore, the device with KAc CBL exhibits superior long-term thermal stability. The findings offer a versatile material to simultaneously passivate interfacial and bulk defects and thus enhance the performance of all-inorganic PSCs.

Lead-free tin perovskite solar cells

Enhanced performance of CsPbBr3 perovskite solar cells by reducing the conduction band offsets via a Sr-modified TiO2 layer

Electron transport layer (ETL) is one of the most essential layers in determining photovoltaic (PV) performance of perovskite solar cells (PSCs). The role of the ETL is to facilitate the charge collection in the device. Studies have shown that the use of tin oxide (SnO2) as ETL could improve the efficiency and stability of PSCs while reducing their degradation. In this work, the Solar Cell Capacitance Simulator (SCAPS-1D) is utilized to investigate the performance of PSCs with SnO2 as the ETL. The device is composed of FTO (Contact)/SnO2 (ETL)/CH3NH3PbI3 (Perovskite)/Cu2O (HTL)/Au (Contact). The effects of thickness, dopant concentration, and defect density of the SnO2 ETL on the performance of PSCs have been investigated. From the results, the optimum parameters for the SnO2 ETL have been identified at thickness of 10 nm, dopant concentration of 1 ×1017 cm−3 and defect density of 1 ×1014 cm−3. With the optimized parameters, the final performance of the PSC demonstrates power conversion efficiency (PCE) of 18.31%.

Recently, it has been demonstrated that the use of SnO2 as the electron transport layer (ETL) of perovskite (PSK) solar cells (PSCs) yields high efficiency, which is comparable to that of the TiO2 layer with the same structure. At the same time, the SnO2-based PSCs show improved stability. Herein, the defects at the device interface are reduced and the efficiency of the planar PSCs is enhanced by improving the interface contact between the ETL and the perovskite (PSK) layer. As an essential amino acid, tyrosine (Tyr) is introduced into SnO2 to fill the oxygen vacancies in SnO2 films and improve the nucleation of PSK. From our analysis, it was found that the interface contact between the SnO2 ETL and the PSK layer was increased and the defects at the interface were reduced. In addition, it was demonstrated that the introduction of Tyr could effectively suppress the charge recombination and improve the electron extraction efficiency. As a result, a champion power conversion efficiency (PCE) of 22.17% was obtained from Tyr modified PSCs, owing to the enhanced PSK film quality and carrier extraction efficiency. On top of that, the Tyr-modified device still maintained 87% of the initial recorded PCE, which was stored in the ambient air (25 °C, 25% ± 5% RH) for 864 h without encapsulation.

Effect of doping engineering in TiO2 electron transport layer on photovoltaic performance of perovskite solar cells

Fabrication of gradient band tin oxide electron transport layer using self-separated dual-quantum dots for perovskite solar cells

Buried modification with tetramethylammonium chloride to enhance the performance of perovskite solar cells with n-i-p structure

Dual modification engineering enabled efficient perovskite solar cells with high open-voltage of 1.233 V

Boosting performance of perovskite solar cells with Graphene quantum dots decorated SnO2 electron transport layers

Organometal hybrid perovskite material has emerged as an attractive competitor in the field of photovoltaics due to its promising potential of low-cost and high-efficiency photovoltaic applications. Although organometal halide perovskite solar cell shows great potential to meet future energy needs, the degradation raises serious questions about its commercialization viability. At present, the stability of perovskite solar cells has been studied in various environmental conditions. Nonetheless, an understanding of the degradation and its performance of CH3NH3PbI3-xClx perovskite solar cell is limited. Herein, we report the mechanical and structural degradation of CH3NH3PbI3-xClx perovskite films at room temperature as a function of time and thermal instability of perovskite solar cells during the heating and cooling processes. For mechanical degradation measurement, we used nanoindentation for CH3NH3PbI3-xClx perovskite films fabricated on FTO/PEDOT:PSS substrate. The hardness and elastic modulus of perovskite films were measured as a function of time. In addition, the mechanical degradation of perovskite thin films was correlated with X-ray diffraction, steady-state and time-resolved photoluminescence (PL). We also investigated the thermal instability of perovskite thin films and the irreversible performance of perovskite solar cells. Particularly, the irreversible performance of CH3NH3PbI3-xClx was analyzed by measuring the development of crystallinity, charge trapping/detrapping, trap depth, and PbI- phase while varying the temperature of perovskite films and solar cells between room temperature and 82 °C. Surprisingly, we found that the degradation of both perovskite films and solar cells occurred at ~70°C. Remarkably, even after the perovskite solar cell temperature cooled down to room temperature, the performance of solar cells continuously degraded. The underlying mechanism of irreversibly degraded performance of perovskite films and solar cells were explained in terms of the development of phase separation, increased trapping rates and deep trap depth of defect states of perovskite films.

In recent years, organic-inorganic hybrid perovskite solar cells have aroused the interest of a large number of researchers due to the advantages of large optical absorption coefficient, tunable bandgap and easy fabrication. Recently, the power conversion efficiency of organic-inorganic hybrid perovskite solar cells has been enhanced to more than 23% in laboratory. In solution processed perovskite solar cells, perovskite and charge transport layer are stacked together, due to the different crystallization rates leading to lattice mismatch near the surface region of perovskite film, resulting in a lot of interface defects, especially at the interface between perovskite and charge transport layer. What is more, the photo-induced free carriers must transfer across the interfaces to be collected. But the defects near the interface can trap photogeneration electrons, thus reducing the carrier lifetime and causing the charges to be recombined, which greatly influence the performance and stability of perovskite solar cells. Therefore, reducing and passivating these defects is critical for obtaining the high performance perovskite solar cells. Now, there have been made tremendous efforts devoting to advancing passivation techniques, such as doping and surface modification, for high efficiency perovskite solar cell with improved stability and reduced hysteresis. These approaches also contribute to improving the energy band alignment between carrier transport layers and perovskite absorber improving device performance, or resistance moisture to enhance device stability. In this review we mainly introduce the formation and the effect of defects on perovskite solar cells, analyze the mechanism for passivating the interfacial defects between charge transport layer and perovskite photo absorption layer for different materials, compare the effects of different passivation materials on the photovoltaic performance of perovskite solar cells, and summarize the role of these materials in passivating the defects. Finally we discuss the research trend and development direction of passivation defects in perovskite solar cells.

Charge extraction by electron transport layers (ETLs) plays a vital role in improving the performance of perovskite solar cells (PSCs). Here, PSCs with four different types of ETLs, such as SnO2, amorphous‐Zn2SnO4 (am‐ZTO), am‐ZTO/SnO2, and SnO2/am‐ZTO, are successfully synthesized. The interface recombination behavior and the charge transport properties of the devices affected by four types of ETLs are systematically investigated. For dual am‐ZTO/SnO2 ETLs, compact am‐ZTO ETL prepared by the pulsed laser deposition method provides a dense physical contact with FTO than the spin coating films, decreasing leakage current and improving charge collection at the interface of ETL/FTO. Moreover, dual am‐ZTO/SnO2 ETLs lead to large free energy difference (ΔG), improving electron injection from perovskite to ETLs. One additional electron pathway from perovskite to am‐ZTO is formed, which can also improve electron injection efficiency. A power conversion efficiency of 20.04% and a stabilized efficiency of 19.17% are achieved for the device based on dual am‐ZTO/SnO2 ETLs. Most importantly, the devices are fabricated at a low temperature of 150 °C, which offers a potential method for large‐scale production of PSCs, and paves the way for the development of flexible PSCs. It is believed that this work provides a strategy to design ETLs via controlling ΔG and interface contact to improve the performance of PSCs.