Enhanced hole extraction in green energy perovskite solar cell by CuOx/spiro-OMeTAD bilayer with improved performance

Lead-free tin perovskite solar cells

Two-dimensional Bi2OS2 doping improves the performance and stability of perovskite solar cells

The numerical simulation tool SCAPS-1D was used to analyze perovskite solar cell having the architecture ITO/ PEDOT:PSS or GO /CH3NH3PbI3-xClx/ PCBM /Au contains inverted planar hetero-junction device. In this work, we investigated the effect of inserting the Graphene Oxide (GO) as Hole Transport layer (HTL) on the performance of perovskite solar cells. Simulation results show that the use of GO as a hole transport layer is efficient. The efficiency of PSCs based on GO HTL was increased by about 1.6 % compared to the conventional PEDOT:PSS HTL device. The obtained results of optimizing the thickness of GO HTL exhibited an optimum value around 10 nm with an efficiency of 12.35 %, Voc of 1.19 V and FF of 54.8 %. We have also shown that the performance of device for high GO carrier density is a better than with low ones. In addition, increasing the temperature beyond the optimum value obtained around 320 K for both HTL materials (GO and PEDOT:PSS) has detrimental effect on the performance of the perovskite solar cells however the device is more sensitive to the temperature with PEDOT:PSS than the GO ones. The effect of band gap of GO on the performance of device is also studied. The obtained results underline the determining role playedby this parameter with an optimum value around 3.25 eV.

Introduction The NiOx layer is actively used as hole extraction layer for inverted structure perovskite solar cells. However, clear guidelines on NiOx chemical composition, manufacturing methods, energy levels, and the hole-transport process remain unclear. In this conference, high-density NiOx layers with various manufacturing temperatures are produced with Nickel acetylacetonate using the SPD method in order to improve the performances of inverted perovskite solar cells. The chemical composition of the NiOx is investigated using XPS, and GIXRD. Furthermore, the influence of Na+ ions in the valence band of the NiOx layer is investigated by vacuum ultraviolet photoelectron spectroscopy using synchrotron radiation. The results showed that the conversion efficiency of the perovskite solar cell is high as the crystallite size of NiOx is large. The highest perovskite solar cell conversion efficiency was obtained at a NiOx layer production temperature of 550 °C. Inverted perovskite solar cells were fabricated with over 16.1% conversion efficiency. Conversion efficiency of solar cell The conversion efficiencies of the perovskite solar cells using NiOx films with various deposition temperatures are summarized in Table 1. The perovskite solar cells conversion efficiency increased along with the NiOx layer production temperature to 550 and 600 °C; however, it decreased slightly when the temperature increased further to 600 °C. As a result, the perovskite solar cell conversion efficiency reached its peak when the NiOx layer production temperature was 500 °C. To highlight the performance change, we herein investigated the composition, structure and the band state of the NiOx layers. Influence of valence band and valence of Ni ion of the NiOx layers To investigate the states of the regions near the edges of the valence bands of the NiOx layers, PES measurements were carried out with a BL-07B at the NewSUBARU synchrotron radiation facility, and the results are shown in Figure 1. The regions near the edges of the valence bands of the NiOx correspond to Ni 3d (label A), O 2p (label B), and the charge transfer transition from an O 2p level to Ni 3d photoionization (label C). From the PES measurement results, the region (around 4-5 eV) corresponding to O 2p was stronger at 300 and 600 °C than at 500 °C. This is because the influence of the O 2p orbital increased because the proportion of oxygen in NiOx increased owing to the loss of Ni ions. Although the ratio of Ni2+ to Ni3+ ions affects the energy levels in the vicinity of the HOMO, a change in these energy levels does not contribute to hole extraction in perovskite solar cells. From these results, it was found that the valence of the Ni ions has little influence on the performance of the solar cells. Crystal analysis of the NiOx layers Both the structures and crystallite sizes of the thin NiOx films formed by SPD were investigated via GIXRD, as shown in Figure 2. The five peaks that appeared at 2θ values of approximately 37.6° 43.6°, 63.3°, 75.6°, and 79.6° were assigned to the 111, 200, 220, 311, and 222 planes, respectively, and then attributed to the randomly oriented NiOx crystal. At 250 °C, no diffraction peaks were observed because the NiOx film did not crystallise. This implies that crystallised NiOx films formed with annealing temperatures above 300 °C. The NiOx crystallite sizes were calculated from the intensities of the 200 peaks using the Scherrer equation, and the results are shown in Figure 1, which indicates that their sizes increased with increasing SPD temperatures. The size of a NiOx crystallite and the tendency of conversion efficiency were consistent, except at 550 and 600 °C, where the FTO layer broke beyond the glass transition point. In other words, as a guideline for manufacturing high-performance inverted perovskite solar cells, it is important to enlarge the crystallites in the NiOx film. Conclusions We demonstrated that it is related to the NiOx crystallite size and the conversion efficiency of the perovskite solar cells, which can be used as a guideline to achieve high performance. The highest perovskite solar cell conversion efficiency was obtained at a NiOx layer production temperature of 500 °C. In the inverse perovskite solar cell, the conversion efficiency exceeded 16.1%, and hysteresis was not observed. Moreover, the measurements of the valence band using synchrotron radiation indicated that the ratio of Ni2+ to Ni+3 had little effect on the solar cell performance. This is an important guideline for improving the performance of perovskite solar cells. Acknowledgement This work was supported by New energy and industrial Technology Development Organization (NEDO), Japan.

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.

Enhanced hole extraction by NiO nanoparticles in carbon-based perovskite solar cells

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.

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

Solar electricity is an unlimited source of sustainable fuels, yet the efficiency of solar cells is limited. The efficiency of perovskite solar cells improved from 3.9% to reach 25.5% in just a few years. Perovskite solar cells are actually viewed as promising by comparison with dye-sensitized solar cells, organic solar cells, and the traditional solar cells made of silicon, GaAs, copper indium gallium selenide (CIGS), and CdTe. Here, we review bare and doped metal oxide electron transport layers in the perovskite solar cells. Charge transfer layers have been found essential to control the performance of perovskite solar cells by tuning carrier extraction, transportation, and recombination. Both electron and hole transport layers should be used for charge separation and transport. TiO2 and 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene are considered as the best electron and hole transport layers. Metal oxide materials, either bare or doped with different metals, are stable, cheap, and effective.

Improving performance of perovskite solar cells based on ZnO nanorods via rod-length control and sulfidation treatment

18 - Perovskite solar cells: A review of architecture, processing methods, and future prospects

Transparent Sn-doped In2O3 electrodes with a nanoporous surface for enhancing the performance of perovskite solar cells

Inferior morphology of perovskite films and suppressed hole extraction restricts the performance of perovskite solar cells (PSCs) with a PEDOT:PSS hole transporting layer (HTL). In this work, poly-TPD is used to modify the surface of PEDOT:PSS films in PSC. The presence of hydrophobic poly-TPD decreases the nucleation sites, and as a result, perovskite films with larger grains are obtained. Improved energy level alignment in the presence of poly-TPD results in enhanced hole extraction from the perovskite layer to the HTL. The improved morphology and charge extraction resulted in improved photovoltaic performance. The power conversion efficiency (PCE) of PSCs was increased from 13.6% to 16.1% with the incorporation of poly-TPD. Also, the shelf life of the PSCs has exhibited considerable improvement due to the presence of hydrophobic poly-TPD and fewer number of grain boundaries. After 66 days, the PSC with poly-TPD maintained 96% of its initial PCE, whereas the PCE of the control device degraded to 72% of its initial value.

As we move towards the commercialization and upscaling of perovskite solar cells, it is essential to fabricate them in ambient environment rather than in the conventional glove box environment. The efficiency of ambient-processed perovskite solar cells lags behind those fabricated in controlled environments, primarily owing to external environmental factors such as humidity and temperature. In the case of device fabrication in ambient environments, relying solely on a single parameter, such as temperature or humidity, is insufficient for accurately characterizing environmental conditions. Therefore, the dew point is introduced as a parameter which accounts for both temperature and humidity. In this study, a machine learning model was developed to predict the efficiency of ambient-processed perovskite solar cells based on meteorological data, particularly the dew point. A total of 238 perovskite solar cells were fabricated, and their photovoltaic parameters and dew points were collected from March to December 2023. The collected data were used to train various tree-based machine learning models, with the random forest model achieving the highest accuracy. The efficiencies of the perovskite solar cells fabricated in January and February 2024 were predicted with a MAPE of 4.44%. An additional Shapley Additive exPlanations analysis confirmed the significance of the dew point in the performance of perovskite solar cells.

As a low-cost, high stable hole transport material, nickel oxide has been widely used in inverted structure perovskite solar cells in recent years. By far, the most common method of preparing nickel oxide hole transport layers is spin-coating pre-prepared nickel oxide nanoparticles (NiO<sub><i>x</i></sub> NPs), which puts forward high requirement for the particle sizes and solution processing capabilities of NiO<sub><i>x</i></sub> NPs. In this work, the sizes of NiO<sub><i>x</i></sub> NPs are precisely controlled by adjusting the pH value of the system in the synthesis process, and high-quality nickel oxide hole transport layers are then prepared. The experimental results exhibit that the NiO<i>x</i> NPs with sizes of 5–10 nm are obtained at a pH value in a range of 9.5–9.8. More interestingly, the obtained NiO<sub><i>x</i></sub> NPs have good dispersion stability and can achieve long-term dispersion in aqueous solution. Furthermore, the structural composition analysis of NiO<sub><i>x</i></sub> NPs shows that the pH value of the synthesis system does not have a significant effect on the material structure nor composition of the NiO<sub><i>x</i></sub> NP. Surface morphological analysis shows that the NiO<sub><i>x</i></sub> film prepared by the pH-controlled NiO<sub><i>x</i></sub> NPs is rather dense and particularly flat with small surface roughness. It is also found that the film exhibits good hole extraction capability. We also fabricate an inverted perovskite solar cell based on the NiO<sub><i>x</i></sub> film. The device structure is ITO/NiO<sub><i>x</i></sub>/CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>/PC61BM/Bphen/Ag. It yields a good photovoltaic conversion efficiency (17.39%). In addition, the device is almost hysteresis-free. Our experimental results exhibit that the performance of perovskite solar cells can be effectively improved by precisely controlling the sizes of NiO<sub><i>x</i></sub> NPs through pH values. Our work is expected to facilitate the development of NiO<sub><i>x</i></sub>-based perovskite solar cells.