All-inorganic Perovskite Solar Cells Research Articles

Synergistic passivation by alkali metal and halogenoid ions for high efficiency HTM-free carbon-based CsPbI2Br solar cells

Hole transport material (HTM)-free carbon-based all-inorganic perovskite solar cells (C-PSCs) possess excellent thermal stability and low cost, which promise an alternative to replace the conventional organic–inorganic hybrid PSCs. The additive method is an effective approach to enhance the performance of PSCs by improving the quality of perovskite films. Herein, the synergistic passivation strategy of alkali metal and halogenoid ions in NaSCN additive is adopted to suppress nonradiative recombination in CsPbI2Br films. The Na+ is incorporated at the A-site of CsPbI2Br cell that enhances the I− diffusion barrier energy from 0.229 eV to 0.401 eV, suggesting suppressed iodide vacancy. Moreover, the SCN− plays a role in regulating the crystal growth dynamics during the CsPbI2Br film formation process, reducing defect density. This synergistic passivation strategy effectively improves the perovskite film quality, and increases the recombination resistance and the carrier extraction efficiency of CsPbI2Br films, therefore reducing nonradiative recombination loss in the final device. The assembled HTM-free carbon-based all-inorganic CsPbI2Br perovskite solar cells present a champion PCE of 14.63% (VOC = 1.267 V, JSC = 14.31 mA/cm2, fill factor (FF) = 0.807), which is among the best performances in the carbon-based all-inorganic perovskite solar cells.

Performance Enhancement of All-Inorganic Carbon-Based CsPbIBr2 Perovskite Solar Cells Using a Moth-Eye Anti-Reflector.

All-inorganic carbon-based CsPbIBr2 perovskite solar cells (PSCs) have attracted increasing interest due to the low cost and the balance between bandgap and stability. However, the relatively narrow light absorption range (300 to 600 nm) limited the further improvement of short-circuit current density (JSC) and power conversion efficiency (PCE) of PSCs. Considering the inevitable reflectance loss (~10%) at air/glass interface, we prepared the moth-eye anti-reflector by ultraviolet nanoimprint technology and achieved an average reflectance as low as 5.15%. By attaching the anti-reflector on the glass side of PSCs, the JSC was promoted by 9.4% from 10.89 mA/cm2 to 11.91 mA/cm2, which is the highest among PSCs with a structure of glass/FTO/c-TiO2/CsPbIBr2/Carbon, and the PCE was enhanced by 9.9% from 9.17% to 10.08%. The results demonstrated that the larger JSC induced by the optical reflectance modulation of moth-eye anti-reflector was responsible for the improved PCE. Simultaneously, this moth-eye anti-reflector can withstand a high temperature up to 200 °C, and perform efficiently at a wide range of incident angles from 40° to 90° and under various light intensities. This work is helpful to further improve the performance of CsPbIBr2 PSCs by optical modulation and boost the possible application of wide-range-wavelength anti-reflector in single and multi-junction solar cells.

Ambient processed and stable all-inorganic lead halide perovskite solar cells with efficiencies nearing 20% using a spray coated Zn1−xCsxO electron transport layer

Achieving ambient-processed and stable all-inorganic halide perovskite solar cells with high conversion efficiencies is a well-established goal within the halide perovskite research community. In striving for this, electron transporting layers based on common TiO2 and SnO2 nanoparticles have been widely deployed, however, can stifle device performance due to their requirement for high temperature processing and non-uniform layer deposition. Using a low-temperature processed Cs-doped ZnO nanocrystalline electron transport layer and a narrow-bandgap (~1.70 eV) all-inorganic absorber (Cd-doped CsPbI2.5Br0.5), we report ambient-processed solar cells which exhibit high conversion efficiencies (>19.75%) and stable performance under ambient condition (>300 h). A smooth interface is established by combining spray-deposition of the electron transport layer and injection of hot-air during the perovskite deposition, which crystallizes smooth, compact perovskite thin films directly from solution. The high performance is attributed to preserving a solar-friendly and phase-stable perovskite layer, along with improved charge carrier management.

MAAc Ionic Liquid-Assisted Defect Passivation for Efficient and Stable CsPbIBr2 Perovskite Solar Cells

Cesium-based all-inorganic perovskite solar cells (PSCs), such as CsPbIBr2 PSCs, have attracted wide attention for good thermal and wet stability, but the low open-circuit voltage (Voc) mainly caused by the inadequate coverage of CsPbIBr2 films is the main reason for limiting their development. The CsPbIBr2 films grown on TiO2 substrate directly have a large number of pinholes, which bring a lot of defects and lead to an increase of nonradiative recombination. In this work, a strategy extended for CsPbIBr2 films by precoating methylammonium acetate (MAAc) ionic liquid onto a TiO2 layer before depositing the CsPbIBr2 film is demonstrated. The uniformly distributed MA+ will be the nucleation center at the bottom of the CsPbIBr2 film, which exhibited a notable impact on the crystallization kinetics of CsPbIBr2 films. This effect simultaneously enhanced the crystal quality of the CsPbIBr2 film and interfacial contact between the electron transporting layer (ETL) and CsPbIBr2 layer. It is instrumental in decreasing the trap state density, suppressing nonradiative recombination, and extracting the charge carriers. Therefore, the stability of the optimized device has been improved considerably, and the champion power conversion efficiency (PCE) is up to 8.85% with a high Voc of 1.26 V. Benefiting from passivation, the PSC with 2 M MAAc IL interfacial modification remains 82% of its initial PCE after 30 days of exposing the device to ambient air at room temperature.

Multifunctional fluorinated ammonium salt for high-performance all-inorganic CsPbI2Br perovskite solar cells with efficiency of 16.29%

All-inorganic CsPbI2Br material has attracted considerable attention due to its good balance between phase stability and absorption capacity. However, the power conversion efficiency (PCE) and device stability of CsPbI2Br-based perovskite solar cells (PSCs) still lag far behind those of their counterparts, mainly deriving from the notoriously poor moisture stability under humid environment and large serious charge recombination. Herein, a typical phenethylammonium chlorine (PEACl) and its fluorinated derivative 4-fluoro-phenethylammonium chlorine (F-PEACl) are individually incorporated to modify the surface of CsPbI2Br film to ameliorate the above issues. Benefiting from the comprehensive passivation effect of ammonium halogen, the trap states of treated CsPbI2Br are vastly suppressed. In particular, fluorination significantly increased the dipole moment and hydrophobic property of F-PEACl. Thus, the present CsPbI2Br PSC achieves a champion PCE of 16.29% with high open-circuit voltage of 1.272 V, while the reference device and PEACl-treated device yield PCEs of 14.30% and 15.64%, respectively. More importantly, the PSC with F-PEACl capping layer retains 87.2% of its initial PCE after 1000 h storage under 20% RH ambient without encapsulation. Our results reveal the underlying mechanism of performance improvement by surface passivation strategy and provide an effective approach to further boost the CsPbI2Br PSC efficiency and stability.

Improved open-circuit voltage of CsPbI3 quantum dot solar cells by PMMA interlayer

All-inorganic CsPbI3 quantum dots perovskite solar cells (QDPSCs) have wide potential application due to their excellent photoelectric properties with high environmental stability. However, the poor interface contact between the light absorption layer and hole transport layer (HTL) results in the serious carrier recombination and the large open-circuit voltage (VOC) loss. Herein, we introduce the insulating PMMA (poly(methyl methacrylate)) buffer layer into CsPbI3 quantum dots (QDs)/Cu12Sb4S13 QDs HTL interface in all-inorganic QDPSCs with the structure of FTO/c-TiO2/m-TiO2/CsPbI3 QDs/Cu12Sb4S13 QDs/Au. The interface carrier recombination is obviously suppressed and the significant VOC improvement from 1.04 V to 1.14 V is obtained with the incorporated PMMA buffer layer. The devices with PMMA buffer layer show the enhanced power conversion efficiency (PCE) of 10.99%, and the improvement of 9.71% is achieved compared to that of the control devices (10.02%). The stability is significantly enhanced due to the intrinsic hydrophobic characteristic of PMMA, and the devices retain 62.69% of their initial PCE after stored in air condition for 15 days, which is greatly improved compared with the control device without PMMA.

Novel ytterbium-doped CsPbI2Br thin-films–based inorganic perovskite solar cells toward improved phase stability

In this study, we used ytterbium (Yb2+) as a dopant in the CsPbI2Br inorganic perovskite thin film and stabilized its black phase. Here, we varied the Yb2+ doping concentration in the CsPb1−xYbxI2Br (x = 0–0.04) perovskite phase through simple solution method. The optimum concentration of Yb2+ showed improved morphology and crystal growth. The fabricated all-inorganic perovskite solar cells (IPVSCs) having CsPb0.97Yb0.03I2Br-based champion device showed the highest 15.41% power conversion efficiency (PCE) for a small area of 0.09 cm2 and 14.04% PCE for a large area of 1 × 1 cm2 with excellent reproducibility, which is higher than the controlled CsPbI2Br device. Detailed photovoltaic analysis revealed that the PCE, open-circuit voltage (VOC), short circuit current density (JSC) and fill factor (FF) of the final IPVSC device attributed to the suppressed charge recombination, better film quality, and well growth orientation of the perovskite film. Moreover, the champion CsPb0.97Yb0.03I2Br device retains >85% initial efficiency after 280 h under 85 °C thermal annealings. Our results provide a new method to boost the performance of the photovoltaic application.

Design and Numerical Investigation of a Lead-Free Inorganic Layered Double Perovskite Cs4CuSb2Cl12 Nanocrystal Solar Cell by SCAPS-1D.

In the last decade, perovskite solar cells have made a quantum leap in performance with the efficiency increasing from 3.8% to 25%. However, commercial perovskite solar cells have faced a major impediment due to toxicity and stability issues. Therefore, lead-free inorganic perovskites have been investigated in order to find substitute perovskites which can provide a high efficiency similar to lead-based perovskites. In recent studies, as a kind of lead-free inorganic perovskite material, Cs4CuSb2Cl12 has been demonstrated to possess impressive photoelectric properties and excellent environmental stability. Moreover, Cs4CuSb2Cl12 nanocrystals have smaller effective photo-generated carrier masses than bulk Cs4CuSb2Cl12, which provides excellent carrier mobility. To date, there have been no reports about Cs4CuSb2Cl12 nanocrystals used for making solar cells. To explore the potential of Cs4CuSb2Cl12 nanocrystal solar cells, we propose a lead-free perovskite solar cell with the configuration of FTO/ETL/Cs4CuSb2Cl12 nanocrystals/HTL/Au using a solar cell capacitance simulator. Moreover, we numerically investigate the factors that affect the performance of the Cs4CuSb2Cl12 nanocrystal solar cell with the aim of enhancing its performance. By selecting the appropriate hole transport material, electron transport material, thickness of the absorber layer, doping densities, defect density in the absorber, interface defect densities, and working temperature point, we predict that the Cs4CuSb2Cl12 nanocrystal solar cell with the FTO/TiO2/Cs4CuSb2Cl12 nanocrystals/Cu2O/Au structure can attain a power conversion efficiency of 23.07% at 300 K. Our analysis indicates that Cs4CuSb2Cl12 nanocrystals have great potential as an absorbing layer towards highly efficient lead-free all-inorganic perovskite solar cells.

Simulated development and optimized performance of narrow-bandgap CsSnI3-based all-inorganic perovskite solar cells

As perovskite solar cell (PSC) technology is about to be commercialized, the use of toxic and organic material is still a problem. At the same time, CsSnI3 has received widespread attention because of its narrow bandgap and non-toxicity. In this study, we use the wxAMPS tool to investigate the limitations of Sn-based all-inorganic PSCs, using CsSnI3 perovskite as the absorption layer and Au as the back electrode to create non-toxic all-inorganic PSCs. CsSnI3 is a narrow-band material; the absorption range can be extended to the near-infrared spectral region, and it has a very high hole mobility. Therefore, this article first compares several potential inorganic electron and hole transport layers (ETLs and HTLs), and the results show that C60 ETL and MoOx HTL are the most suitable materials. Moreover, the device performance is further improved by optimizing the absorber thickness as well as the doping density. Under optimized conditions, a conversion efficiency of 19.25% is obtained for the FTO/C60/CsSnI3/MoOx/Au PSCs, indicating that there is much room for further performance enhancement. The photovoltaic performance parameters achieve their optimum value at an absorber thickness is better among the range of 100–1300 nm and doping density of 1019 cm−3. This shows that the proposed non-toxic all-inorganic PSCs have broad prospects in future photovoltaic and optoelectronics applications, and provide theoretical guidance for the manufacture of a non-toxic and inorganic PSCs.

Construct efficient CsPbI2Br solar cells by minimizing the open-circuit voltage loss through controlling the peripheral substituents of hole-transport materials

In order to further boost the photovoltaic performance of all-inorganic perovskite solar cells (PSCs), great efforts are needed to synergistically develop high-quality perovskite film and highly efficient charge transport materials. In view of the fact that large number of researchers have devoted to optimizing the crystal composition and crystallization kinetics, we chose to carry out the study from the perspective of hole transport layer. Herein, we designed and synthesized two low-cost fluorene terminal-modified hole transport materials (HTMs), termed YT-MPF and YT-FF. Moreover, through the modification of peripheral groups, the electrostatic surface potentials of HTMs are well regulated. The HTM YT-MPF with one peripheral fluorene arm on each side exhibits a more polarized structure, which facilitates the intermolecular interaction and hole hopping transport. Applied YT-MPF in CsPbI2Br based all-inorganic PSC, an impressive power conversion efficiency (PCE) of 16.0% with fairly high open-circuit voltage (Voc) of 1.29 V is obtained, outperforming that of the control devices based on traditional HTM PTAA (12.7%) and Spiro-OMeTAD (14.7%). Our research supplies an effective way to push up the performance of CsPbI2Br PSC.

Design of Low Bandgap CsPb1- x Snx I2 Br Perovskite Solar Cells with Excellent Phase Stability.

Novel all-inorganic Sn-Pb alloyed perovskites are developed aiming for low toxicity, low bandgap, and long-term stability. Among them, CsPb1- x Snx I2 Br is predicted as an ideal perovskite with favorable band gap, but previously is demonstrated unable to convert to perovskite phase by thermal annealing. In this report, a series of CsPb1- x Snx I2 Br perovskites with tunable bandgaps from 1.92 to 1.38eV are successfully prepared for the first time via low annealing temperature (60°C). Compared to the pure CsPbI2 Br, these Sn-Pb alloyed perovskites show superior stability. Furthermore, a novel α-phase-stabilization mechanism of the inorganic Sn-Pb alloyed perovskite by reconfiguring the perovskite crystallization process with chloride doping is provided. Simultaneously, a dense protection layer is formed by the coordination reaction between the surface lead dangling bonds and sulfate ion to retard the permeation of external oxygen and moisture, leading to less oxidation of Sn2+ in perovskite film. As a result, the fabricated all-inorganic Sn-Pb perovskite solar cells (PSCs) show a champion power conversion efficiency of 10.39% with improved phase stability and long-term ambient stability against light, heat, and humidity. This work provides a viable strategy in fabricating high-performance narrow-bandgap all-inorganic PSCs.

All-inorganic perovskite solar cells with efficiency >20%

All-inorganic perovskite solar cells with efficiency >20%

An ultraviolet-ozone post-treatment to remove the inherent impurities in all-ambient solution-processed CsPbBr3 perovskite films

It is very important to exclude impurities during the material preparation process for the production of high-quality optoelectronic devices. For the all-ambient solution-processed CsPbBr3 films, unexpected inherent impurities could be inadvertently introduced, which would induce electronic trap states and impede carrier transport in the as-derived CsPbBr3-based optoelectronic devices, such as all-inorganic perovskite solar cells (PSCs). Herein, it is found that ultraviolet-ozone (UVO) post-treatment, which is usually applied for cleaning substrates, has the ability to remove these harmful impurities in all-ambient solution-processed CsPbBr3 films. Upon proper UVO post-treatment, the assembled PSC with the architecture of fluorine-doped tin oxide/compact TiO2 (c-TiO2)/CsPbBr3/carbon exhibits an improved power conversion efficiency of 7.82% from 7.37%. X-ray photoelectron spectroscopy measurements demonstrate that the undesirable inherent impurities in all-ambient solution-processed CsPbBr3 films may be related to organic solvents and adsorbates, which can be removed effectively by UVO post-treatment. After UVO post-treatment, photoluminescence and space-charge-limited current measurements reveal that CsPbBr3 films possess reduced trap states. Meanwhile, due to the enhanced contact between the CsPbBr3 film and the subsequently deposited carbon electrode, the charge collection at the interface is effectively promoted. Our work not only finds the influence of the inherent impurities residual in all-ambient solution process, but also proposes a simple and effective strategy to remove these impurities.

Photochemically-Induced Phase Segregation of Mixed Halide Perovskite Solar Cells

The emerging low cost perovskite solar cell quickly reached power conversion efficiency (PCE) parity with crystalline Si solar cells [1]. Optional bandgap tuning of the perovskites by partial substitution of I- with Br- expand their application to tandem solar cells and LEDs. The only critical issue remaining to solve is their poor long term stability under operational conditions, specifically photochemical degradation by splitting into I- and Br- rich phases. Sufficient suppression of this process requires a thorough understanding of the underlying phenomena. Here we report the detailed investigation of the photoinduced phase transformation in stoichiometric and non-stoichiometric mixed halide CsPbI3-xBrx. Using in-situ Atomic Force Microscopy, we visualized real-time kinetics of halide phase segregation under illumination. The I-rich phase segregated predominantly along grain boundaries while the grain bulk remained enriched with Br. It was proposed that photogenerated Pb0 and I3 - species are selectively expelled from grain bulk into grain boundary resulting in the phase splitting. This work supports our focus in understanding degradation mechanisms in perovskite materials for next generation solar cells [2-3].[1] Best Research-Cell Efficiency Chart | Photovoltaic Research | NREL, (n.d.). https://www.nrel.gov/pv/cell-efficiency.html (accessed October 12, 2019).[2] Akbulatov, A.; Frolova, L.; Dremova, N.; Zhidkov, I.; Martynenko, V.; Tsarev, S.; Luchkin, S.; Kurmaev, E.; Aldoshin, S.; Stevenson, K. J.; Troshin, P. “Light or Heat: What Is Killing Lead Halide Perovskites Under Solar Cell Operation Conditions?," J. Phys. Chem. Lett. 2020, 11(1), 333-339.[3] Frolova, L. A.; Luchkin, S. Yu; Akbulatov, A. F.; Dremova, N. N.; Stevenson, K. J.; Troshin, P. A. “Efficient and Stable All-Inorganic Perovskite Solar Cells Based on Nonstoichiometric CsxPbI2Brx (x>1) Alloy,” J. Mater. Chem. A 2019 , 7(18), 5314-5323.

Multifunctional liquid additive strategy for highly efficient and stable CsPbI2Br all-inorganic perovskite solar cells

CsPbI2Br all-inorganic perovskite has attracted considerable attention due to its high thermal stability and suitable bandgap, while the unsatisfactory crystallization quality and moisture instability significantly hinder its further application. Herein, a novel multifunctional liquid additive, 2-hydroxyethyl methacrylate (HEMA), is introduced into the CsPbI2Br precursor to ameliorate the above issues. Our results demonstrate that the functional groups of HEMA can interact with perovskite precursor, thus improving crystallization and passivating defects at the same time, and leading to a champion power conversion efficiency of up to 16.13%. Importantly, HEMA molecule in perovskite films will polymerize to a hydrophobic polymer at grain boundaries through breaking C = C bonds during the high temperature annealing process (160 °C). Moreover, this multifunctional liquid additive strategy endows perovskite films with promoted moisture tolerance by crosslinking perovskite grains and blocking moisture penetration, thus the unencapsulated device maintains 78% of its initial efficiency after aging at 30% relative humidity for 1000 h. These results demonstrate that the additive engineering with multifunctional molecule is applicable strategy for developing CsPbI2Br all-inorganic perovskite solar cells with both high efficiency and stability.

Improved Photovoltaic Performance of CsPbI2Br Perovskite Films via Bivalent Metal Chloride Doping

Cesium-based all-inorganic perovskite absorbers have attracted increasing attention due to their superior thermal stability, compared to their organic–inorganic counterparts. Up to now, it is a challenge to fabricate high-efficiency all-inorganic perovskite solar cells (PSCs) with low defect densities. Herein, we used bivalent metal chloride salts (SrCl2 and NiCl2) to optimize CsPbI2Br films. The experimental results indicate that this method could deliver high-quality films with improved electronic property. As a result, the champion device based on the 0.01 M SrCl2–doped CsPbI2Br film achieved a power conversion efficiency (PCE) of 16.07% with a high open voltage (VOC) of 1,322 mV, which is about 18% higher than that of the pristine device.

All-inorganic CsPbBr3 perovskite solar cells with enhanced efficiency by exploiting lone pair electrons via passivation of crystal boundary using carbon nitride (g-C3N4) nanosheets

Fast extraction of photo-generated charge plays a crucial function in improving the photovoltaic conversion efficiency (PCE) of the perovskite solar cells (PSCs). Here, an effective strategy to decrease the charge recombination losses by introducing versatile carbon nitride (g-C3N4) nanosheets to the CsPbBr3 films was demonstrated. The incorporation of the g-C3N4 additive can restrain the nucleation and crystalline growth rate of perovskite films by an interaction of lone pair electrons from the exposed N atoms to the PbBr2 precursor, resulting in high-quality CsPbBr3 films with an increase in crystalline size. Notably, a ‘coupling effect’ between the lone pair electrons from g-C3N4 nanosheets and unsaturated Pb dangling bonds (Br vacancies) around the grain boundaries significantly decreases trap states caused by defects, leading to the fewer recombination centers in CsPbBr3 films. The g-C3N4 nanosheets serving as an energy barrier can also successfully suppress the recombination loss of back electrons with holes from the g-C3N4 interface, yielding a superior PCE of 8.0% with a fill factor of 80.25%. The result opens an alternative path to enhance the performance of CsPbBr3 PSCs by passivating the trap states of perovskite films with the improvement of the crystallization quality and charge extraction efficiency.

Efficient (>20 %) and Stable All-Inorganic Cesium Lead Triiodide Solar Cell Enabled by Thiocyanate Molten Salts.

Besides widely used surface passivation, engineering the film crystallization is an important and more fundamental route to improve the performance of all-inorganic perovskite solar cells. Herein, we have developed a urea-ammonium thiocyanate (UAT) molten salt modification strategy to fully release and exploit coordination activities of SCN- to deposit high-quality CsPbI3 film for efficient and stable all-inorganic solar cells. The UAT is derived by the hydrogen bond interactions between urea and NH4 + from NH4 SCN. With the UAT, the crystal quality of the CsPbI3 film has been significantly improved and a long single-exponential charge recombination lifetime of over 30 ns has been achieved. With these benefits, the cell efficiency has been promoted to over 20 % (steady-state efficiency of 19.2 %) with excellent operational stability over 1000 h. These results demonstrate a promising development route of the CsPbI3 related photoelectric devices.

Defect engineering on all-inorganic perovskite solar cells for high efficiency

Defect engineering on all-inorganic perovskite solar cells for high efficiency

Simulation and optimization studies on CsPbI3 based inorganic perovskite solar cells

Cesium lead iodide (CsPbI3) based perovskite solar cell (PSC) with inorganic electron and hole transport layers is simulated using SCAPS 1D to find optimum performance conditions for an all-inorganic PSC with maximum stability and efficiency. In this study, the absorption spectrum and bandgap of CsPbI3 absorber layer are computed with the help of density functional theory and the resulting spectrum is used as an input for device simulation. Further improvement of device performance is done by optimizing the work function of back electrode, absorber thickness, doping density as well as defect density. Under optimized conditions, a conversion efficiency of 11.99% is obtained with gold (Au) as back contact metal. The efficiency is enhanced to 15.6% for the FTO/ZnO/CsPbI3/CuSbS2/Se configuration, which uses Se instead of Au as back contact metal, indicating the possibility of replacing the expensive Au with Se as back contact metal in PSCs. The photovoltaic performance parameters achieve their maximum value at an absorber thickness of 547 nm and defect and dopant density of 2.07 × 1014 cm−3 and 1 × 1015 cm−3 respectively. The study shows that the PCE of inorganic CsPbI3 based PSCs can be improved significantly by introducing a low cost back contact metal Se and using inorganic transport materials, ZnO and CuSbS2.