Initial Power Conversion Efficiency Value Research Articles

Design tungsten oxides hole transport layers (HTLs) to modify the back interface in all-inorganic carbon-based CsPbBr3 solar cells

To enhance the inferior photovoltaic performance of all-inorganic carbon-based perovskite solar cells (C-PSCs) caused by inefficient charge extraction and transport processes of the CsPbBr3/carbon back interface, three types of tungsten oxides (WO3, WO2.72, WO2) are synthesized as low cost and stable hole transport layers (HTLs) to modify the back interface by tunning the energy level alignment. Among the three kinds of tungsten oxides, WO3 shows the best hole extraction and transport capability and the C-PSCs using WO3 HTL generates a power conversion efficiency (PCE) of 7.90% with a high open circuit voltage (Voc) of 1.307 V, indicating a great PCE enhancement of 43.9%, as compared with the device without HTL (5.49%). Meanwhile, WO2.72 and WO2 also are also proved to be qualified HTLs and the devices show PCE values of 7.57% and 6.24%, respectively. Importantly, WO3 and WO2.72 based device show excellent stabilities with PCE retention over 90% of the initial PCE values under ambient conditions for 60 days.

Synergistic strategies to unveil the dual influence of additive and annealing treatment on the morphology of isatin-derived low bandgap small molecule donor in solution-processed organic solar cells

A novel organic small molecule, 5-(4-(diphenylamino)phenyl)-1-octylindoline-2,3-dione (TPI) containing an alkyl chain substituted electron accepting isatin (indoline-2,3-dione) and strong electron withdrawing N, N-diphenylaniline units have been synthesized through Suzuki coupling reaction. The molecular structure of TPI is confirmed by NMR, FT-IR, and Mass spectroscopy techniques. The TPI molecule exhibits a low band gap of approximately ∼ 2.03 eV which is also supported by the DFT results. The influence of additive and heat treatment on the electronic, morphological, and photovoltaic performance of organic solar cells was investigated meticulously. The TPI donor exhibits complementary light absorption with fullerene acceptor in combination with DIO and TA which efficiently absorb the photon in the 300–730 nm range. The TPI was later used as an electron donor material for the fabrication of organic solar cells. Remarkably, the morphology-dependent optimized TPI:PC71BM (1:3.0) exposed excellent power conversion efficiency (PCE) of about ∼ 5.56 % with enhanced VOC of ∼ 0.811 V, JSC of 11.81 mA cm−2 and FF of 55.3 % fabricated in addition with DIO and thermal annealing treatment. Most importantly, the unencapsulated devices maintained > 96 % of the initial PCE value after 240 h under ambient temperature. Our findings indicate that isatin-derived small molecules with simple architecture propose great potential for promising BHJ-OSCs material.

Zwitterion Dual-Modification Strategy for High-Quality NiOx and Perovskite Films for Solar Cells.

Nickel oxide (NiOx ) has been limited in use as a hole transport layer for its low conduction, surface defects, and redox reactions with the perovskite layer. To address these issues, the incorporation of zwitterion L-tryptophan (Trp) is proposed at the NiOx /Trp interface. The carboxyl group of Trp effectively passivates the surface positive defects of NiOx , thereby improving its optical and electrical properties. The ammonium group of Trp not only passivates negative defects but modulates the growth of the perovskite layer, resulting in an improved perovskite film quality. Furthermore, the Trp layer acts as a buffer layer, suppressing adverse interfacial reactions between the perovskite and NiOx . Consequently, perovskite solar cells with 1.56 and 1.68eV absorbers achieve the champion power conversion efficiency(PCE) of 23.79% and 20.41%, respectively. Moreover, the unencapsulated devices demonstrate excellent long-term stability, retaining above 80% of the initial PCE value after 1600 h of storage in the air with a humidity of 50-60%.

N-Type Small Molecule Electron Transport Layers with Excellent Surface Energy and Moisture Resistance Siloxane for Non-Fullerene Organic Solar Cells.

Electron transport layers (ETLs) generally contain polar groups for enhancing performance and reducing the work function. Nevertheless, the polar group with high surface energy may cause inferior interfacial compatibility, which challenges the ETLsto balance stability and performance. Here, two conjugated small molecules of ETLs with low surface energy siloxane, namely PDI-Si and PDIN-Si, are synthesized. The siloxane with low surface energy not only enhances the interfacial compatibility between ETLs and active layers but also improves the moisture-proof stability of the device. Impressively, the amine-functionalized PDIN-Si can simultaneously exhibit conspicuous n-type self-doping properties and outstanding moisture-proof stability. The optimization of interfacial contact and morphology enables the PM6:Y6-based OSC with PDIN-Si to achieve a power conversion efficiency (PCE) of 15.87%, which is slightly superior to that of classical ETL PDINO devices (15.27%), and when the PDIN-Si film thickness reaches 28nm, the PCE remains at 13.19% (≈83%), which indicates that PDIN-Si has satisfactory thickness insensitivity to facilitate roll-to-roll processing. Excitingly, after 120 h of storage in an environment with humidity above 45%, the unencapsulated device with PDIN-Si as ETL remains at 75% of the initial PCE value, while the device with PDINO as ETL is only 50%.

Indium Zinc Tin Oxide Bottom Electrode‐Based Flexible Indoor Organic Photovoltaics with Remarkably High Mechanical Stability

The demand for flexible indoor organic photovoltaic cells (OPVs) is growing dramatically due to their simple and practical use as a powering aid for various electronic gadgets connected to the Internet of Things. Due to the brittleness of inorganic material‐based transparent bottom electrodes and their incompatibility with flexible organic substrates, it is extremely difficult to limit the influence of mechanical stress on the stability of flexible OPV. In this regard, choosing a mechanically stable and highly conductive transparent conducting oxide (TCO) is crucial. Therefore, flexible OPVs are fabricated onto a flexible (polyimide) substrate coated with mechanically stable TCO indium zinc tin oxide (IZTO). Sheet resistance measurements and observations of scanning electron microscope images of IZTO film after 100 000 bending repetitions (bending radius: 5 mm) confirm the ultrahigh mechanical stability of the TCO. The sheet resistance of flexible IZTO electrode layers is increased by 9%, from 17.42 to 19.12 Ω sq−1. In addition, the impact of a large number of bending repetitions on film transmittance is minimal. The OPV shows ≈69% and ≈20% of its initial power conversion efficiency value after 100 000 bending repetitions for 1000 lx LED illumination and 1 sun conditions, respectively.

Triple hole transporting and passivation layers for efficient NiOX-based wide-bandgap perovskite solar cells

In order to fabricate nickel oxide (NiOX)-based perovskite solar cells with high efficiency and stability, adverse reaction and lattice mismatch are two urgent problems to be overcome. In this respect, interface engineering was carried out by multi-layer passivation NiOX HTLs (NiOX/2PACz/Poly-TPD/PEAI) to provide optimized interface contact between NiOX and perovskite, ameliorate band alignment, and saturate the defect states. Application of 2PACz avoids direct contact of the hydroxyl groups (which causes degeneration of a device), improves conductivity, and reduces interfacial defects. The poly-TPD modification can provide an appropriate band alignment at the interface of NiOX/perovskite. PEAI was used to modify the Poly-TPD surface, and its −NH3 group can passivate unbonded Pb ions of perovskite. Thus, compared with previously reported single-function passivation materials, the multilayer passivation proposed in this paper integrates multiple functions. As a result, the NiOX/2PACz/Poly-TPD/PEAI-based wide bandgap PSCs obtain a champion power conversion efficiency (PCE) of 20.21% and maintain over 95% of their initial PCE values after storage in a nitrogen atmosphere for 1000 h. This finding provides a practical approach for fabricating high-performance regular PSCs with NiOX-based HTLs and supports their commercialization.

Overcoming the PCBM/Ag Interface Issues in Inverted Perovskite Solar Cells by Rhodamine‐Functionalized Dodecahydro‐Closo‐Dodecaborate Derivate Interlayer

AbstractEfficient modification of the interface between metal cathode and electron transport layer are critical for achieving high performance and stability of the inverted perovskite solar cells (PSCs). Herein, a new alcohol‐soluble rhodamine‐functionalized dodecahydro‐closo‐dodecaborate derivate, RBH, is developed and applied as an efficient cathode interlayer to overcome the (6,6)‐phenyl‐C61 butyrie acid methyl ester (PCBM)/Ag interface issues. By introducing RBH cathode interlayer, the functions of the interface traps passivation, interfacial hydrophobicity enhancement, interface contact improvement as well as built‐in potential enhancement are realized at the same time and thus correspondingly improve the device performance and stability. Consequently, a power conversion efficiency (PCE) of 21.08% and high fill factor of 83.37% are achieved, which is one of the highest values based on solution‐processed MAPbI3/PCBM heterojunction PSCs. Moreover, RBH can act as a shielding layer to slow down moisture erosion and self‐corrosion. The PCE of the RBH devices still maintain 84% for 456 h (85 °C @ N2), 87% for 360 h (23 °C @ relative humidity (RH) 35%) of its initial PCE value, while the control device can only maintain ≈23%, 58% of its initial PCE value under the same exposure conditions, respectively.

Efficient and Stable Carbon-Based Perovskite Solar Cells Enabled by Mixed CuPc:CuSCN Hole Transporting Layer for Indoor Applications

Perovskite solar cells (PSCs) are an innovative technology with great potential to offer cost-effective and high-performance devices for converting light into electricity that can be used for both outdoor and indoor applications. In this study, a novel hole-transporting layer (HTL) was created by mixing copper phthalocyanine (CuPc) molecules into a copper(I) thiocyanate (CuSCN) film and was applied to carbon-based PSCs with cesium/formamidinium (Cs0.17FA0.83Pb(I0.83Br0.17)3) as a photoabsorber. At the optimum concentration, a high power conversion efficiency (PCE) of 15.01% was achieved under AM1.5G test conditions, and 32.1% PCE was acquired under low-light 1000 lux conditions. It was discovered that the mixed CuPc:CuSCN HTL helps reduce trap density and improve the perovskite/HTL interface as well as the HTL/carbon interface. Moreover, the PSCs based on the mixed CuPc:CuSCN HTL provided better stability over 1 year due to the hydrophobicity of CuPc material. In addition, thermal stability was tested at 85 °C and the devices achieved an average efficiency drop of approximately 50% of the initial PCE value after 1000 h. UV light stability was also examined, and the results revealed that the average efficiency drop of 40% of the initial value for 70 min of exposure was observed. The work presented here represents an important step toward the practical implementation of the PSC as it paves the way for the development of cost-effective, stable, yet high-performance PSCs for both outdoor and indoor applications.

Interfacial Engineering of Au@Nb2CTx-MXene Modulates the Growth Strain, Suppresses the Auger Recombination, and Enables an Open-Circuit Voltage of over 1.2 V in Perovskite Solar Cells

Defects at the interface of charge transport layers can cause severe charge accumulation and poor charge transferability, which greatly affect the efficiency and stability of stannic oxide (SnO2)-based perovskite solar cells (PSCs). Herein, a new type of MXene (Nb2CTx-MXene) is applied to the interface of SnO2 layers to passivate the interfacial defects and promote charge transport. Nb2CTx-MXene in PSCs realizes the role of boosting the conductivity, reducing the tin vacancies in the interstitial void of the SnO2 layer, decreasing the defect density, and aligning the bandgap. Afterward, Nb2CTx-MXene is decorated with gold nanospheres, which has the ability to modulate the tensile strain of perovskites and suppress the Auger recombination. Eventually, the Au@Nb2CTx-MXene-modified device yields an excellent power conversion efficiency (PCE) of 23.78% with a relatively high open-circuit voltage of 1.215 V (Eg ∼ 1.60 eV). The unencapsulated devices maintain 90% of their initial PCE values after storage in the air with a relative humidity of 40% for 1000 h and remain above 80% of their initial efficiency after operation at the maximum power point for 500 h under 1 sun illumination. Our work provides an avenue to fabricate high-efficiency and stable PSCs with MXene adapting to commercial development.

Silicon/nickel oxide core/shell nanospheres as a hole transport layer for high efficiency and light-stable perovskite solar cells.

Metal halide perovskite solar cells (PSCs) possess huge potential due to their high power conversion efficiency. However, instability is still a key factor limiting their applications. Therefore, we have found a feasible strategy to improve the light stability of PSCs. Specifically, a core-shell material with a silicon nanosphere core and a nickel oxide nanosheet shell serves as the hole transport layer in our PSCs. Due to the selective absorption of ultraviolet light by the silicon nanoparticles, the ultraviolet light content of the natural light that reaches the perovskite layer is reduced. Compared with a control device (without Si), the PSCs with the silicon/nickel oxide hole transport layer possessed a higher current density of 22.09 mA cm-2 and a higher power conversion efficiency of 18.54%, with both values increased by 2.7% and 6.1%, respectively. More importantly, the PSCs based on a silicon/nickel oxide hole transport layer maintains 85% of its initial power conversion efficiency value after 700 hours of natural light exposure. These results indicate that the silicon/nickel oxide hole transport layer is an important functional component of the PSCs, which improves the photovoltaic performance and reduces ultraviolet light-induced photodegradation, thereby improving the device stability.

Synergistic dual-interface modification strategy for highly reproducible and efficient PTAA-based inverted perovskite solar cells

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)-based inverted perovskite solar cells (PSCs) are the most efficient device type reported to date. Nevertheless, the high hydrophobicity of PTAA and the nonradiative recombination loss significantly limit the repeatability and the performances of these devices. In this study, polyvinyl oxide (PEO) and tetra-n-propylammonium bromide (TPAB) were introduced to overcome the hydrophobicity of PTAA and the anode and cathode interface nonradiative recombination losses through the synergistic effect of these materials. The results showed that the PEO could dramatically improve the wetting properties of the perovskite precursor on the PTAA surface, correspondingly enhancing the microstructure of the film, eliminating the defects, and enhancing the anode interfacial contact of the device. The performances and performance repeatability of the devices were greatly improved. The ratio of the short-circuited devices decreased from 44.23 % to 0 %, and the average power conversion efficiency (PCE) increased dramatically. In addition, a facile TPAB surface treatment strategy was proposed to reduce the potential threat of PEO introduction to the device stability as well as improve the cathode interface contact problems of the device. Owing to the synergistic effect of the PEO and TPAB, the performance and stability were both enhanced. The highest PCE of 21.62 % was achieved, and the average PCE of TPAB devices could be maintained at 80 % for 298 h (in air, 23 °C, 25 RH%) and 96 % for 217 d (in N2, 23 °C) of the initial PCE value. The synergistic dual-interface modification strategy proposed in this paper lights the way for the preparation of highly reproducible, efficient, and stable PTAA-based inverted perovskite solar cells.

Improving the Performance of Invert Perovskite Solar Cell Devices By a Multifunctional Ammonium Salt

In past years, halide perovskite solar cells (PSCs) have attracted much attention and are considered as the next-generation solar cells due to their excellent performance. Compared to the conventional structure, the inverted perovskite solar cell device has great potential in large-scale practical applications due to the low-temperature manufacturing process. However, the power conversion efficiency (PCE) is still lower than conventional structure devices, which is because of the high trap density in the surface and grain boundary of perovskite film. One kind of defect is the iodine vacancy caused by methylammonium iodide (MAI) volatilization during perovskite film annealing. I- could be oxidized into I2 and then volatilize out during the perovskite film annealing, the vacancy of I- could form trap states in the surface and grain boundary of the perovskite film. The surface traps induce many defects and increase the charge recombination rate in the inverted polycrystalline perovskite film, which causes PCE loss in the devices. Although lots of efforts are to improve the PCE of devices, perovskite solar cell device is still hard to practical applicate due to poor stability under light exposure conditions. Under light soaking especially UV light, perovskite film would degrade which means I3 - easily change to I2 and induce the lattice defects of perovskite film, which further influence the performance of PSCs. Herein, we present a strategy to suppress the I2 generation to decrease the trap density, reduce the charge recombination in perovskite film and further improve the performance of devices by an ammonium salt named tetrabutylammonium chloride (TBACl) modified. The PCE of devices increase from 18.52% to 20.36% after TBACl was modified, and TBACl also reduce the Voc loss in the perovskite solar cell devices. Furthermore, TBACl passivation enhances the light stability of devices and slows down PSCs degradation with UV light soaking. Because TBACl distributes in the surface and GBs of perovskite film that could absorb the UV light and decrease the effects on the perovskite layer. Benefiting from the influence of TBACl on perovskite solar cell devices, the devices could maintain over 90% with light soaking 120 h and UV light irradiation 450 min, respectively. However, the control devices only could maintain ~47% and ~51% of the initial PCE values under light exposure and UV light soaking conditions, respectively. Thus, we provide a low-cost, easy, and effective post-treatment strategy to enhance the device performance and improve the light stability of perovskite solar cell devices.

Bulk Restructure of Perovskite Films via Surface Passivation for High‐Performance Solar Cells

AbstractDefects in perovskite films and the suboptimal interface contact largely limit the performance and stability of inverted perovskite solar cells (PSCs). A simple surface post‐treatment with N‐benzyloxycarbonyl‐d‐valine (NBDV) is developed to overcome these problems. The device performance following NBDV treatment is systemically investigated. It is showed that NBDV surface post‐treatment results in the bulk restructure of the entire perovskite film and improves the film‐forming property of [6,6]‐phenyl‐C61‐butyric acid methyl ester. The grain sizes, crystallinity, trap states, cathode interfaces, as well as the built‐in field are also improved, which result in PSC performance and stability enhancement. A relatively higher power conversion efficiency (PCE) of 21.80% is reached, which is comparable to the PCE record based on single‐crystal MAPbI3. Meanwhile, the PCE of the NBDV devices can retain ≈77% and 84% of the initial value after storage for 768 h (32 days) in air and 8376 h (349 days) in N2, respectively, while the control devices only maintain ≈53% and 38% of their initial PCE values under the same exposure conditions. This work provides means to promote bulk, surface, and interface regulation toward high performance and stable inverted PSCs.

Perovskite films passivated by a dendrimer toward high efficiency and high stability devices

Passivation engineering has become one of the most effective and convenient strategies to enhance the performance and the stability of perovskite solar cells (PSCs). We design a new material, fatty acid-polyamidoamine-COOH (FPC), with sixteen long alkyl chains and eight carboxylic acid functional groups. The carboxylic acid can passivate the Pb defects at the surface and grain boundaries (GBs). Self-arrangement of the FPC molecules on the surface results in improved surface potential. FPC passivation leads to suppressed charge recombination, enhanced charge carrier transport, and increased light-harvesting. The transient absorption measurements confirm the key role of FPC passivation on the recombination at the interface between perovskite and PC61BM layer in PSCs. The power conversion efficiency (PCE) of PSCs modified by FPC increases to 21.01% with Jsc 23.74 mA/cm2, Voc 1.09 V, and FF 81.16%. Furthermore, the hydrophobic long alkyl chains improve the device stability. Under 60 ± 5% relative humidity (RH), the PSCs with FPC passivation maintain ∼90% of the initial PCE for 3500 min, but the control PSCs only keep ∼50% of the origin PCE. In addition, the devices modified by FPC could maintain ∼82% of the initial PCE value under 25 ± 5% (RH) and 30 ± 5 °C ambient environment for 30 days. This work provides a guideline for designing passivants to improve the efficiency and stability of devices.

Halide anions engineered ionic liquids passivation layer for highly stable inverted perovskite solar cells

Long-term stability remains a great challenge for metal halide perovskite solar cells (PSCs). The utilization of ionic liquids (ILs) is a promising strategy to solve the stability problem. However, few studies have focused on controlling the halide anions of ILs, in which different organic cations can modulate the melting point of ILs and film crystal growth. Here, ILs with a 1-ethyl-3-methylimidazolium (EMIM+) cation and different halide anions (X = Cl, Br, and I) are employed in inverted PSCs. The results show that EMIMX can form a 1D passivation layer by the in situ growth technique and influence the surface morphology of the perovskite film. These EMIMX-treated layers simultaneously suppress the surface defects and nonradiative energy losses and improve the hydrophobic properties. As a result, a power conversion efficiency (PCE) of 20.0% is obtained for the EMIMBr-modified PSCs compared to 18.06% for the control device. Moreover, the unencapsulated devices maintain more than 90% of their initial PCE over 3000 h under ambient air, which is among the best long-term stabilities reported for NiOx-based inverted PSCs. It also retains 74.2% and 49.5% of the initial PCE value after aging under harsher conditions, such as an 85 ± 5% relative humidity (RH) environment and at 85 °C for 48 h, respectively.

Elimination of Interfacial Lattice Mismatch and Detrimental Reaction by Self‐Assembled Layer Dual‐Passivation for Efficient and Stable Inverted Perovskite Solar Cells

AbstractInterfacial lattice mismatch and adverse reaction are the key issues hindering the development of nickel oxide (NiOx)‐based inverted perovskite solar cells (PVSCs). Herein, a p‐chlorobenzenesulfonic acid (CBSA) self‐assembled small‐molecule (SASM) is adopted to anchor NiOx and perovskite crystals to endow dual‐passivation. The chlorine terminal of SASMs can provide growth sites for perovskite, leading to interfacial strain release. Meanwhile, the sulfonic acid group from SASMs can passivate surface defects of NiOx, conducive to charge carrier extraction. In addition, the self‐assembled layer inhibits the adverse interfacial reaction by preventing NiOx contact with perovskite. Therefore, the NiOx/CBSA‐based PVSCs obtain a champion power conversion efficiency (PCE) of 21.8%. Of particular note, the unencapsulated devices can retain above 80% of their initial PCE values after storage in a nitrogen atmosphere for 3000 h, in air with a relative humidity of 50–70% for 1000 h, and heating at 85 °C for 800 h, respectively.

Highly Efficient and Stable CsPbTh3 (Th = I, Br, Cl) Perovskite Solar Cells by Combinational Passivation Strategy.

The distorted lead iodide octahedra of all‐inorganic perovskite based on triple halide‐mixed CsPb(I2.85Br0.149Cl0.001) framework have made a tremendous breakthrough in its black phase stability and photovoltaic efficiency. However, their performance still suffers from severe ion migration, trap‐induced nonradiative recombination, and black phase instability due to lower tolerance factor and high total energy. Here, a combinational passivation strategy to suppress ion migration and reduce traps both on the surface and in the bulk of the CsPhTh3 perovskite film is developed, resulting in improved power conversion efficiency (PCE) to as high as 19.37%. The involvement of guanidinium (GA) into the CsPhTh3 perovskite bulk film and glycocyamine (GCA) passivation on the perovskite surface and grain boundary synergistically enlarge the tolerance factor and suppress the trap state density. In addition, the acetate anion as a nucleating agent significantly improves the thermodynamic stability of GA‐doped CsPbTh3 film through the slight distortion of PbI6 octahedra. The decreased nonradiative recombination loss translates to a high fill factor of 82.1% and open‐circuit voltage (V OC) of 1.17 V. Furthermore, bare CsPbTh3 perovskite solar cells without any encapsulation retain 80% of its initial PCE value after being stored for one month under ambient conditions.

Enhanced Perovskite Solar Cell Performance via 2-Amino-5-iodobenzoic Acid Passivation.

The intrinsic stability issues of the perovskite materials threaten the efficiency and stability of the devices, and stability has become the main obstacle to industrial applications. Herein, the efficient and facile passivation strategy by 2-amino-5-iodobenzoic acid (AIBA) is proposed. The impact of AIBA on the properties of the perovskite films and device performance is systemically studied. The results show that the trap states are eliminated without affecting the crystal properties of the perovskite grains, leading to the enhanced performance and stability of the perovskite solar cells (PSCs). A high power conversion efficiency (PCE) of 20.23% and lower hysteresis index (HI) of 1.49‰ are achieved, which represent one of the most excellent PCE and HI values for the inverted PSCs based on MAPbI3/[6,6]-Phenyl-C61-Butyric Acid Methyl Ester (PCBM) planar heterojunction structure. Moreover, the UV stability of the perovskite films and the thermal and moisture stability of the devices are also enhanced by the AIBA passivation. The PCE of the device with AIBA can maintain about 83.41% for 600 h (40 RH %) and 64.06% for 100 h (55-70 RH %) of its initial PCE value without any encapsulation, while the control device can maintain only about 72.91 and 45.59% of its initial PCE. Density functional theory calculations are performed to study the origins of enhanced performance. Interestingly, the results show that the surface states induced by AIBA can facilitate the photoexcited charge transfer dynamics and reduce the electron-hole recombination loss. The passivation method developed in this work provides an efficient way to enhance the stability and performance of inverted PSCs.

A Trifluoroethoxyl Functionalized Spiro‐Based Hole‐Transporting Material for Highly Efficient and Stable Perovskite Solar Cells

It is crucial to finely optimize the properties of hole transport materials (HTMs) to improve the performance and stability of perovskite solar cells (PSCs). Herein, a new spiro‐based HTM (Spiro‐4TFETAD) is developed by replacement of partial methoxy groups in Spiro‐OMeTAD with trifluoroethoxy substituents. Spiro‐4TFETAD has lower highest occupied molecular orbital level, higher thermal stability (Tg = 140 °C), hole mobility (2.04 × 10−4 cm2 V−1 s−1), and better hydrophobicity with respect to Spiro‐OMeTAD. The PSCs using Spiro‐4TFETAD achieve a power conversion efficiency of 21.11% and excellent humidity resistance. It maintains an average 83% of their initial power conversion efficiency values even in high relative humidity of 60% without encapsulation and 82% of its initial performance after 100 h continuous illumination at the maximum power point. The superior performance underscores the promising potential of the trifluoroethoxyl molecular design in preparing new HTMs toward highly efficient and stable PSCs.

Defect passivation and interface modification by tetra-n-octadecyl ammonium bromide for efficient and stable inverted perovskite solar cells

Charge recombination loss caused by defects and interfaces in the inverted perovskite solar cells (PSCs) significantly impact cell performance and stability. Here, a kind of quaternary ammonium salt of tetra-n-octadecyl ammonium bromide (TODB) with an symmetrical structure is introduced into inverted PSCs to suppress the charge recombination loss. We have comprehensively studied the impact of TODB on the physical properties of the perovskite films and corresponding the performance of the devices. TODB post-treatment results in defect passivation, the built-in electric field enhancement as well as hydrophobicity improvement in the inverted PSCs, which correspondingly enhance device performance and stability. The highest power conversion efficiency (PCE) reaches 20.36 %, which is one of the highest PCE of the inverted PSCs based on methylammonium lead iodide (MAPbI3)/phenyl-C61-butyric acid methyl ester (PCBM) planar heterojunction. The device with TODB modification can maintain 80 % of its initial PCE value in the air for 384 h, while the control device only maintains about 52 % of its initial PCE under the same exposure conditions. This work presents an efficient strategy to improve the performance and stability of the PSCs by passivating the trap states at the interfaces and increasing the hydrophilicity of the perovskite films.