Inverted Structure Perovskite Solar Cells Research Articles

Enhancement of inverted structure perovskite solar cell by CZTS nanoparticles

Inverted structure perovskite solar cells have attracted much attention in recent years due to their reliable operational stability, low residual, and low-temperature fabrication process. In the past few years, to accelerate their commercialization, the focus of research on the inverted structure perovskite solar cells was on the power conversion efficiency increasing. In this study nanoparticles of Cu2ZnSnS4 (CZTS) were doped into the PEDOT:PSS film as the hole transport layer (HTL) and then the interface carrier recombination quenching was observed. Consequently, it leads the s to charge carrier's collection enhancement of the Inverted perovskite solar cells. Compared to other types of HTLs, the use of CZTS HTL reduces the amount of interaction of the HTL film and the perovskite film, which results in an increment of the stability of the solar cell over time.

Buried-Interface Engineering Enables Efficient and 1960-HourISOS-L-2I Stable Inverted Perovskite Solar Cells.

High-performance perovskite solar cells (PSCs) typically require interfacial passivation, yet this is challenging for the buried interface, owing to the dissolution of passivation agents during the deposition of perovskites. Here, this limitation is overcome with in situ buried-interface passivation-achieved via directly adding a cyanoacrylic-acid-based molecular additive, namely BT-T, into the perovskite precursor solution. Classical and ab initio molecular dynamics simulations reveal that BT-T spontaneously may self-assemble at the buried interface during the formation of the perovskite layer on a nickel oxide hole-transporting layer. The preferential buried-interface passivation results in facilitated hole transfer and suppressed charge recombination. In addition, residual BT-T molecules in the perovskite layer enhance its stability and homogeneity. A power-conversion efficiency (PCE) of 23.48% for 1.0cm2 inverted-structure PSCs is reported. The encapsulated PSC retains 95.4% of its initial PCE following 1960h maximum-power-point tracking under continuous light illumination at 65°C (i.e., ISOS-L-2I protocol). The demonstration of operating-stable PSCs under accelerated ageing conditions represents a step closer to the commercialization of this emerging technology.

Bowl-Assisted Ball Assembly for Solvent-Processing the C60 Electron Transport Layer of High-Performance Inverted Perovskite Solar Cell.

Pristine fullerene C60 is an excellent electron transport material for state-of-the-art inverted structure perovskite solar cells (PSCs), but its low solubility leaves thermal evaporation as the only method for depositing it into a high-quality electron transport layer (ETL). To address this problem, we herein introduce a highly soluble bowl-shaped additive, corannulene, to assist in C60 -assembly into a smooth and compact film through the favorable bowl-ball interaction. Our results show that not only corannulene can dramatically enhance the film formability of C60 , it also plays a critical role in forming C60 -corannulene (CC) supramolecular species and in boosting intermolecular electron transport dynamics in the ETL. This strategy has allowed CC devices to deliver high power conversion efficiencies up to 21.69 %, which is the highest value among the PSCs based on the solution-processed-C60 (SP-C60 ) ETL. Moreover, the stability of the CC device is far superior to that of the C60 -only device because corannulene can retard and curb the spontaneous aggregation of C60 . This work establishes the bowl-assisted ball assembly strategy for developing low-cost and efficient SP-C60 ETLs with high promise for fully-SP PSCs.

Bowl‐Assisted Ball Assembly for Solvent‐Processing the C60 Electron Transport Layer of High‐Performance Inverted Perovskite Solar Cell

AbstractPristine fullerene C60 is an excellent electron transport material for state‐of‐the‐art inverted structure perovskite solar cells (PSCs), but its low solubility leaves thermal evaporation as the only method for depositing it into a high‐quality electron transport layer (ETL). To address this problem, we herein introduce a highly soluble bowl‐shaped additive, corannulene, to assist in C60‐assembly into a smooth and compact film through the favorable bowl‐ball interaction. Our results show that not only corannulene can dramatically enhance the film formability of C60, it also plays a critical role in forming C60‐corannulene (CC) supramolecular species and in boosting intermolecular electron transport dynamics in the ETL. This strategy has allowed CC devices to deliver high power conversion efficiencies up to 21.69 %, which is the highest value among the PSCs based on the solution‐processed‐C60 (SP‐C60) ETL. Moreover, the stability of the CC device is far superior to that of the C60‐only device because corannulene can retard and curb the spontaneous aggregation of C60. This work establishes the bowl‐assisted ball assembly strategy for developing low‐cost and efficient SP‐C60 ETLs with high promise for fully‐SP PSCs.

Graphene-Like Conjugated Molecule as Hole-Selective Contact for Operationally Stable Inverted Perovskite Solar Cells and Modules.

Further enhancing the operational lifetime of inverted-structure perovskite solar cells (PSCs) is crucial for their commercialization, and the design of hole-selective contacts at the illumination side plays a key role in operational stability. In this work, the self-anchoring benzo[rst]pentaphene (SA-BPP) is developed as a new type of hole-selective contact toward long-term operationally stable inverted PSCs. The SA-BPP molecule with a graphene-like conjugated structure shows a higher photostability and mobility than that of the frequently-used triphenylamine and carbazole-based hole-selective molecules. Besides, the anchoring groups of SA-BPP promote the formation of a large-scale uniform hole contact on ITO substrate and efficiently passivate the perovskite absorbers. Benefiting from these merits, the champion efficiencies of 22.03% for the small-sized cells and 17.08% for 5×5cm2 solar modules on an aperture area of 22.4cm2 are achieved based on this SA-BPP contact. Also, the SA-BPP-based device exhibits promising operational stability, with an efficiency retention of 87.4% after 2000h continuous operation at the maximum power point under simulated 1-sun illumination, which indicates an estimated T80 lifetime of 3175h. This novel design concept of hole-selective contacts provides a promising strategy for further improving the PSC stability.

Bottom-Up Templated and Oriented Crystallization for Inverted Triple-Cation Perovskite Solar Cells with Stabilized Nickel-Oxide Interface.

Inverted-structure perovskite solar cells (PSCs) are known for their superior device stability. However, based on nickel-oxide (NiOx ) substrate, disordered crystallization and bottom interface instability of perovskite film are still the main factors that compromise the power conversion efficiency (PCE) of PSCs. Here, 2D perovskite of thiomorpholine 1,1-dioxide lead iodide (Td2 PbI4 ) is introduced as a template to prepare 3D perovskite thin film with high crystal orientation and large grain size via a bottom-up growth method. By adding TdCl to the precursor solution, pre-crystallized 2D Td2 PbI4 seeds can accumulate at the bottom interface, lowering the barrier of nucleation, and templating the growth of 3D perovskite films with improved (100) orientation and reduced defects during crystallization. In addition, 2D Td2 PbI4 at the bottom interface also hinders the interfacial redox reaction and reduces the hole extraction barrier on the buried interface. Based on this, the Td-0.5 PSC achieves a PCE of 22.09% and an open-circuit voltage of 1.16V. Moreover, Td-0.5 PSCs show extremely high stability, which retains 84% of its initial PCE after 500h of continuous illumination under maximum power point operating conditions in N2 atmosphere. This work paves theway for performance improvement of inverted PSCs on NiOx substrate.

Tailoring Functional Terminals on Solution-Processable Fullerene Electron Transporting Materials for High Performance Perovskite Solar Cells.

Widely known as an excellent electron transporting material (ETM), pristine fullerene C60 plays a critical role in improving the photovoltaic performance of inverted structure perovskite solar cells (PSCs). However, the imperfect perovskite/C60 interface significantly limits the promotion of device performance and stability due to the weak coordination interactions between bare carbon cages and perovskite. Here, we designed and synthesized three functionalized fulleropyrrolidine ETMs (abbreviated as CEP, CEPE, and CECB), each of which was modified with the same primary terminal (cyanoethyl) and various secondary terminals (phenyl, phenethyl, and chlorobutyl). The resulting CECB-based PSC has a power conversion efficiency (PCE) over 19% and exceptional photo-stability over 1800 h. This work provides significant insight into the targeted terminal design of novel fullerene ETMs for efficient and stable PSCs.

Self-assembled interlayer aiming at the stability of NiOx based perovskite solar cells

Inorganic NiOx based inverted structure perovskite solar cells (PSCs) is reported to be more stable than that with the organic hole transport materials. In this work, NiOx/MAPbI3 interface chemical reaction induced instability of perovskite is unveiled: Ni3+ and I− exhibit redox reactions and deprotonation of MA+ happens, which result in interface defects and perovskite lattice deformation. Thus the defective interface accelerates the degradation of perovskite by defect pathways from the bottom interface to the perovskite surface contacting H2O/O2. Self-assembled interlayer of NH2− end silane on NiOx separates the reactive NiOx and MAPbI3, tunes the interface energy states by –NH2 end group. As a result, the PSC based on the silane treated NiOx achieves enhanced PCE of 20.1% with decent stability under environmental and extreme conditions (high temperature, high humidity, light infiltration). Our work highlights the interface chemical problem induced PSC instability and a simple interface modification to achieve the stable PSCs.

Performance of trans perovskite solar cells improved by finely adjusting the particle size of nickel oxide nanoparticles through pH value

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.

Performance of trans perovskite solar cells improved by finely adjusting the particle size of nickel oxide nanoparticles through pH value

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><sub>x</sub></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>/PC<sub>61</sub>BM/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.

Enhancing efficiency and stability of inverted structure perovskite solar cells with fullerene C60 doped PC61BM electron transport layer

[6, 6]-phenyl C61butyric acid methyl ester (PC61BM) is a common fullerene derivative widely employed as an electron transport layer in inverted perovskite solar cells. However, major challenges such as interfacial recombination, current leakage and low mobility results in poor photovoltaic performance and stability for PC61BM-based devices. To overcome these issues, we demonstrated, for the first time, doping of the PC61BM with fullerene C60 to tailor the properties of the PC61BM. This doping approach helped to realize superior power conversion efficiency of perovskite solar cell with 17.46% versus pristine device with 14.20%. The C60 doped PC61BM reinforced the surface morphology of the PC61BM layer with reduced roughness and better coverage, up-shift of Fermi Level, higher electrical conductivity, higher maximum charge carrier generation rate, and higher charge collection probability. All these improvements contributed to reduced charge leakage at the interface, reduced charge recombination and promoted efficient charge transfer, transport, and collection. Furthermore, the enhanced hydrophobicity of the C60 doped PC61BM enabled superior ambient device stability compared to the pristine device. This work facilitates a simple and effective route to tailor perovskite solar cell performance towards higher efficiency and better stability.

Improved photostability of inverted-structure perovskite solar cells with high power conversion efficiency by inserting CuI between PEDOT and MAPbI3 layers

Inverted-structure perovskite devices with PEDOT and PEDOT/CuI as hole transport layers (HTLs) were prepared on Glass/ITO substrates. Surface morphology observation of the CuI revealed that the CuI grew on PEDOT in island mode. A concentration of 20 mg/ml was necessary for continuous CuI formation on the PEDOT. Optimization of the annealing time and the concentration of CuI precursor solution led to a PCE of 16.5% for a device with PEDOT/CuI as HTL, which was slightly higher than that (15%) with PEDOT as HTL. The slight enhancement of PCE was due to the faster hole transport efficiency and improved light-harvesting in the visible light region. Additionally, the photostability of the devices was greatly enhanced by the insertion of the CuI layer. Analysis indicated that the insertion of the CuI decreased the transmittance of light with wavelengths within 320–410 nm, which was the main reason for the enhanced photostability.

Polymer Modification on the NiOx Hole Transport Layer Boosts Open-Circuit Voltage to 1.19 V for Perovskite Solar Cells

Inverted-structure perovskite solar cells (PVSCs) applying NiOx as the hole transport layer (HTL) have attracted increasing attention. It is still a challenge to optimize the contact between NiOx and the perovskite layer and to suppress energy loss at the interface. In this study, interface engineering was carried out by modifying the NiOx layer with different polymers such as polystyrene, poly(methyl methacrylate) (PMMA), or poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) to improve the surface contact between NiOx and the perovskite, to decrease the defect states, and to make the energy level alignment better. The NiOx/PMMA-based device presents a Voc as high as 1.19 V because of the improved interfacial contact and the interaction of the carbonyl and methoxy group with Pb2+. The NiOx/PTAA-based device with the structure ITO/NiOx/PTAA/(MAPbI3)0.95(MAPbBr2Cl)0.05/PCBM/BCP/Ag exhibits the highest power conversion efficiency of 21.56% with a high Voc of 1.19 V. The enhanced performance can be attributed to the deepened highest occupied molecular orbital level of NiOx/PTAA, which matched well with that of the perovskite and suppressed interface energy loss as well. This work provides a facile approach for efficiently improving the Voc of NiOx-based PVSCs.

Small molecular material as an interfacial layer in hybrid inverted structure perovskite solar cells

Hybrid halide perovskites are becoming increasingly popular due to their immense potential to be used as a low cost and easily processable solar cell technology. Interfacial engineering is believed to be one of the crucial ways to improve the device performance. In this work, we report the introduction of a small molecular interfacial layer 4,4’-(naphthalene-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TPA-NAP-TPA) between the traditional hole transporting layer poly (3,4-ethylenedioxythiophene:polystyrene sulfonate) (PEDOT:PSS) and perovskite (Cs0.15FA0.85PbI3) active layer. Systematic investigations indicate that the incorporation of the small molecular interfacial layer improves the inverted device efficiency by 7% relative. The crystallinity and morphology of the perovskite formed on top of the PEDOT:PSS/TPA-NAP-TPA is favourable compared to the perovskite formed on top of pristine PEDOT:PSS layer. The improvement in the PCE is attributed to increased photocurrent generation. The devices containing the interfacial layer has also depicted improved quantum yield which is in line with the maximised average JSC. Furthermore, the devices with PEDOT:PSS/TPA-NAP-TPA interfacial layer retained 60% of their initial efficiency after 30 days, which is 30% higher than the devices with pristine PEDOT:PSS layer. Including interfacial layers such as TPA-NAP-TPA could be a viable technique in order to enhance the performance and stability of inverted structure perovskite solar cells.

Reconfiguration of interfacial energy band structure for high-performance inverted structure perovskite solar cells

Charged defects at the surface of the organic–inorganic perovskite active layer are detrimental to solar cells due to exacerbated charge carrier recombination. Here we show that charged surface defects can be benign after passivation and further exploited for reconfiguration of interfacial energy band structure. Based on the electrostatic interaction between oppositely charged ions, Lewis-acid-featured fullerene skeleton after iodide ionization (PCBB-3N-3I) not only efficiently passivates positively charged surface defects but also assembles on top of the perovskite active layer with preferred orientation. Consequently, PCBB-3N-3I with a strong molecular electric dipole forms a dipole interlayer to reconfigure interfacial energy band structure, leading to enhanced built-in potential and charge collection. As a result, inverted structure planar heterojunction perovskite solar cells exhibit the promising power conversion efficiency of 21.1% and robust ambient stability. This work opens up a new window to boost perovskite solar cells via rational exploitation of charged defects beyond passivation.

Numerical modeling of inverted perovskite solar cell based on CZTSSe hole transport layer for efficiency improvement

In this work, device modeling of inverted-structure perovskite solar cells employing Cu 2 ZnSn ( S x Se 1 − x ) 4 ( CZTS x Se 1 − x ) as hole transport layer (HTL) is performed by SCAPS. The bandgap of CZTS x Se 1 − x can be tuned in a wide range from 0.95 to 1.5 eV through the variation of S doping content, which allows us to adjust the valence band offset (VBO) of the CH 3 NH 3 PbI 3 / CZTS x Se 1 − x interface. Simulation results indicate that a suitable VBO of 0.25 eV is obtained when S/(S + Se) ratio of CZTS x Se 1 − x is 0.6, which yields a cell efficiency of 16.75%. Further optimization of the absorber and HTL thickness and doping density in HTL is conducted. Simulation results indicate that the optimal HTL and absorber thickness of are 30 and 700 nm, respectively. Doping concentration of HTL higher than 10 19 cm − 3 is essential for good device performance. After comprehensive optimization of these parameters, an optimum efficiency of 21.59% is obtained. The research can provide a theoretical guidance for further performance improvement of the device with CZTS <mml:mro

High-performance inverted planar perovskite solar cells based on solution-processed rubidium-doped nickel oxide hole-transporting layer

Abstract Organic–inorganic hybrid perovskite solar cells (PVSCs) have attracted great attention due to the high power conversion efficiency (PCE). For the p-i-n inverted structure PVSCs, the hole transporting layer (HTL) plays an important role in achieving high efficient and stable PVSCs by improving charge extraction, reducing interfacial recombination, and modifying band alignment etc. In this work, rubidium (Rb) doped NiOx (Rb:NiOx) was employed as HTL to study the impacts on the optoelectronic properties and the photovoltaic performance. Both NiOx and Rb:NiOx films were smooth and highly transparent with a simple solution-based method. The Rb:NiOx films exhibited better conductivity and effectively elevated the valence band maximum (VBM). At the same time, the Rb doping induced a better morphology of perovskite film with larger crystals size on top. Therefore, Rb doping resulted in significantly improved hole extraction and reduced recombination losses. As a result, the photovoltaic performance of the PVSCs was remarkably increased from 14.48% to 17.21%.

Design of BCP buffer layer for inverted perovskite solar cells using ideal factor

In the inverted structure perovskite solar cells, a buffer layer is generally used at the interface between the n-type semiconductor layer and the metal electrode, but its design guidelines have not yet been established. Here, a series of inverted perovskite solar cells have been fabricated with the controlled thickness of bathocuproine (BCP) buffer layers deposited by thermal evaporation and validated the BCP buffer layer evaluation tool. The ideal factor was calculated from the gradient in the plot of Voc against the log of Jsc, and the effect of the BCP buffer layer on charge recombination was verified. Since the ideal factor greatly decreased from 5 to 1.4 by introducing the BCP buffer layer, it was confirmed that the interface between the n-type semiconductor layer and the metal electrode gradually changed from a Schottky barrier diode to an ohmic contact. On the other hand, it was found that an excessive BCP film thickness causes the series resistance to increase and induced recombination. Finally, as a result of optimizing the perovskite layer and the BCP buffer layer, respectively, the performance exceeding 17% was obtained. This study provides insight into the improvements in the conversion efficiency of perovskite solar cells by optimizing the thickness of the buffer layer using the ideal factor.

(Invited) Engineering of Nickel Oxide Hole Transport Layer for Inverted Perovskite Solar Cells

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.

Tetrathiafulvalene derivative as a new hole-transporting material for highly efficient perovskite solar cell

Hole-transporting materials play an important role in perovskite solar cells. In this study, we introduced a novel hole-transporting material without p-type dopant, a tetrathiafulvalene derivative anchored with eight carboxyl groups (TTA) into inverted structure perovskite solar cells. The devices with TTA as hole-transporting layer showed high power conversion efficiency of 16.7%, which was 44.5% improvement compared with the reference devices without hole-transporting layer. The performance improvement was ascribed to three factors: 1) the better match of energy level between ITO and perovskite layer; 2) enhanced hole extraction at anode interface; 3) improved perovskite morphology.