Low-Temperature Solution-Processed ZnSe Electron Transport Layer for Efficient Planar Perovskite Solar Cells with Negligible Hysteresis and Improved Photostability

Simulation and optimization of 30.17% high performance N-type TCO-free inverted perovskite solar cell using inorganic transport materials

Perovskite solar cells (PSCs) have gained much attention in recent years because of their improved energy conversion efficiency, simple fabrication process, low processing temperature, flexibility, light weight, and low cost of constituent materials when compared with their counterpart silicon based solar cells. Besides, stability and toxicity of PSCs and low power conversion efficiency have been an obstacle towards commercialization of PSCs which has attracted intense research attention. In this research paper, a Glass/Cu2O/CH3NH3SnI3/ZnO/Al inverted device structure which is made of cheap inorganic materials, n-type transparent conducting oxide (TCO)-free, stable, photoexcited toxic-free perovskite have been carefully designed, simulated and optimized using a one-dimensional solar cell capacitance simulator (SCAPS-1D) software. The effects of layers' thickness, perovskite's doping concentration and back contact electrodes have been investigated, and the optimized structure produced an open circuit voltage (Voc) of 1.0867 V, short circuit current density (JSC) of 33.4942 mA/cm2, fill factor (FF) of 82.88% and power conversion efficiency (PCE) of 30.17%. This paper presents a model that is first of its kind where the highest PCE performance and eco-friendly n-type TCO-free inverted CH3NH3SnI3 based perovskite solar cell is achieved using all-inorganic transport materials.

The effects of grating anatase on the photovoltaic performance of perovskite based solar cells

Stimulated by the extraordinary power conversion efficiency (PCE) of hybrid organic-inorganic perovskites (HOIP) based solar cells (SCs), the derivative studies on inorganic perovskites (IOP) based SCs have been intensely investigated. In order to overcome the disadvantages of CsPbBr₃, most prominently the unfavorable larger band gap (2.3eV), a grating layer of mesoporous anatase TiO₂(mp-TiO₂) has been inserted into the conventional configuration of SCs. The grating layer acts as the electron transfer layer (ETL) and light absorption strengthening layer at the same time. Due to the combined effects, the increased contacting area increased the fill factor (FF) and enhanced light trapping in the grating layer increased the short-current density, the average PCE of IOP based SCs has increased from 5.67% to 7.58%, which is a ca. 34% increase relatively. Furthermore, research on traditional HOIP-based SCs is also conducted. Interestingly, the increasing PCE mechanism is quite different from their inorganic counterparts, which should be attributed to the strain effect of different film structures. Thus, the strain-induced defect charge-state transitions of MAPbI₃ by the grating layer increased the open-circuit voltage (V_oc); and similarly, the increased contacting area also increased the FF, resulting in a 13% increase for PCE.

Recent advances in self-powered and flexible UVC photodetectors

Ultraviolet-C (UVC) radiation is employed in various applications, including irreplaceable applications in military and civil fields, such as missile guidance, flame detection, partial discharge detection, disinfection, and wireless communication. Although most modern electronics are based on Si, UVC detection technology remains a unique exception because the short wavelength of UV radiation makes efficient detection with Si difficult. In this review, recent challenges in obtaining ideal UVC photodetectors with various materials and various forms are introduced. An ideal photodetector must satisfy the following requirements: high sensitivity, fast response speed, high on/off photocurrent ratio, good regional selectivity, outstanding reproducibility, and superior thermal and photo stabilities. UVC detection is still in its infancy compared to the detection of UVA as well as other photon spectra, and recent research has focused on different key components, including the configuration, material, and substrate, to acquire battery-free, super-sensitive, ultra-stable, ultra-small, and portable UVC photodetectors. We introduce and discuss the strategies for fabricating self-powered UVC photodetectors on flexible substrates in terms of the structure, material, and direction of incoming radiation. We also explain the physical mechanisms of self-powered devices with various architectures. Finally, we present a brief outlook that discusses the challenges and future strategies for deep-UVC photodetectors.

BiFeO3 photocathodes for efficient H2O2 production via charge carrier dynamics engineering

Metal oxide semiconductors are promising candidate photoelectrodes for photoelectrochemical H₂O₂ production if the issues of poor efficiency and selectivity can be resolved. An unfavorable charge transport barrier causes poor carrier collection and kinetics, limiting their efficiency and selectivity. Herein, BiFeO₃ was used as the model photocathode, and its interfacial charge transport barrier between fluorine-doped tin oxide substrates was modulated by introducing a LaNiO₃ layer as the charge collection layer. Our findings show the significantly enhanced photoelectrochemical activity of the composite photocathode with an improved photocurrent by three times (-0.9 mA cm^-2 at 0.6 V vs. RHE) and the H₂O₂ formation up to 278 μmol L^-1 with doubled faradaic efficiency. It is shown that these enhancements are due to the promoted charge carrier collection and kinetics. This work demonstrates the significant role of the charge collection layer in improving the collection and usage of photocarriers to accelerate the application of solar-to-fuel conversion.

High-Performance Planar Perovskite Solar Cells with a Reduced Energy Barrier and Enhanced Charge Extraction via a Na2WO4-Modified SnO2 Electron Transport Layer

Tin oxide (SnO₂) has been commonly used as an electron transport layer (ETL) in planar perovskite solar cells (p-PSCs) because it can be prepared by a low-temperature solution-processed method. However, the device performance has been restricted due to the limited electrical performance of SnO₂ and its mismatched energy level alignment with the perovskite absorber. Considering these problems, sodium tungstate (Na₂WO₄) has been employed to modify the SnO₂ ETL. The conduction band minimum of SnO₂ increases and the defects at the ETL/perovskite interface decrease by the modification of the SnO₂ ETL with Na₂WO₄, thus reducing the energy barrier between the ETL and perovskite. In addition, the electron extraction ability has been enhanced and the interface recombination between the ETL and perovskite has also been inhibited. As a result, the photovoltaic performance of p-PSCs based on the modified ETL has been improved, and a champion power conversion efficiency of 21.16% has been achieved compared with the control device of 17.30% with an open circuit voltage increased from 1.075 to 1.162 V.

Orientation Dependent Mechanical Responses and Plastic Deformation Mechanisms of ZnSe Nano Films under Nanoindentation

Although ZnSe has been widely studied due to its attractive electronic and optoelectronic properties, limited data on its plastic deformations are available. Through molecular dynamics simulations, we have investigated the indentations on the (001), (110), and (111) planes of ZnSe nano films. Our results indicate that the elastic modulus, incipient plasticity, elastic recovery ratio, and the structural evolutions during the indenting process of ZnSe nano films show obvious anisotropy. To analyze the correlation of structural evolution and mechanical responses, the atomic displacement vectors, atomic arrangements, and the dislocations of the indented samples are analyzed. Our simulations revealed that the plastic deformations of the indented ZnSe nano films are dominated by the nucleation and propagation of 1/2<110> type dislocations, and the symmetrically distributed prismatic loops emitted during the indenting process are closely related with the mechanical properties. By studying the evolutions of microstructures, the formation process of the dislocations, as well as the formation mechanisms of the emitted prismatic loops under the indented crystalline planes are discussed. The results presented in this work not only provide an answer for the questions about indentation responses of ZnSe nano films, but also offer insight into its plastic deformation mechanisms.

Band Matching Strategy for All-Inorganic Cs2AgBiBr6 Double Perovskite Solar Cells with High Photovoltage

The lead-free double perovskite has been proven to be one of the promising alternatives to solve the stability and toxicity problems of lead-based organic-inorganic hybrid perovskite solar cells. Here, high-quality Cs₂AgBiBr₆ double perovskite films with large grains and smooth surface have been prepared through a sequential-vapor-deposition method, and a low-cost and eco-friendly Cu₂O film with a suitable energy level and good electrical properties was prepared as an efficient hole transport layer by vacuum vapor deposition for the first time. The Cu₂O-based devices achieve a champion power conversion efficiency increasing from 1.03 to 1.52% and an enhancement of photovoltage from 1.083 to 1.198 V compared with their organic counterparts. More importantly, the Cu₂O-based devices have excellent stability; they maintained the initial 96% efficiency under environmental conditions after 33 days of unpackaged storage. These results also point out the direction for the further development of these new promising perovskite solar cells.

In situ synthesis of g-C3N4 by glass-assisted annealing route to boost the efficiency of perovskite solar cells

TiO₂-based electron transport layers (ETLs) show tremendous advantages in constructing efficient perovskite solar cells (PSCs), but the power conversion efficiency (PCE) needs further improvements. Thus, in this study, graphitic carbon nitride (g-C₃N₄), a typical two-dimensional material, was synthesized in-situ and introduced into TiO₂-based ETLs as an additive via a facile glass-assisted annealing route. The results demonstrated that the addition of g-C₃N₄ positively influenced the crystalline quality of the perovskite layers, as well as the conductivity and photovoltaic properties of the devices. Furthermore, favorable energy level alignment facilitated rapid migration of electrons and suppressed charge recombination at the interfaces. Consequently, the champion device fabricated using the g-C₃N₄-modified ETL achieved a maximum PCE of 20.46% owing to the remarkable improvement in the V_oc, J_sc, and fill factor. The PCE is approximately 20% higher than that obtained for the pristine device, i.e., 17.18%.

Device simulation of highly efficient eco-friendly CH3NH3SnI3 perovskite solar cell

Photoexcited lead-free perovskite CH3NH3SnI3 based solar cell device was simulated using a solar cell capacitance simulator. It was modeled to investigate its output characteristics under AM 1.5G illumination. Simulation efforts are focused on the thickness, acceptor concentration and defect density of absorber layer on photovoltaic properties of solar cell device. In addition, the impact of various metal contact work function was also investigated. The simulation results indicate that an absorber thickness of 500 nm is appropriate for a good photovoltaic cell. Oxidation of Sn2+ into Sn4+ was considered and it is found that the reduction of acceptor concentration of absorber layer significantly improves the device performance. Further, optimizing the defect density (1014 cm-3) of the perovskite absorber layer, encouraging results of the Jsc of 40.14 mA/cm2, Voc of 0.93 V, FF of 75.78% and PCE of 28.39% were achieved. Finally, an anode material with a high work function is necessary to get the device's better performance. The high-power conversion efficiency opens a new avenue for attaining clean energy.

Effect of Optimization of TiO2 Electron Transport Layer on Performance of Perovskite Solar Cells with Rough FTO Substrates

The film quality of the electron transport layer (ETL) plays an important role in improving the performance of perovskite solar cells (PSCs). In order to reduce the effect of rough fluorine-doped SnO2 (FTO)substrate on the film quality of the TiO2 ETL, multiple cycles of spin-coating were employed to realize optimized TiO2 film and improve the performance of PSCs with rough FTO. The results show that TiO2 ETL was optimized most effectively using two spin-coating cycles, obtaining the best performance of PSCs with rough FTO. The carbon electrode-based PSCs were then demonstrated. Our work discusses the feasibility of low-quality rough FTO for the fabrication of PSCs and photodetectors to reduce costs.

Photoinduced charge carrier dynamics in a ZnSe quantum dot-attached CdTe system

A new nanohybrid material is prepared by attaching CdTe nanoneedles (NNs) to surface-modified ZnSe quantum dots (QDs). The NNs and QDs are prepared by a colloidal synthesis method in an aqueous alkaline medium. The surface modification and the attachment of nanostructures are achieved by a bifunctional ligand 3-mercaptopropionic acid (3-MPA). The band gap of the ZnSe QDs is varied by controlling the size of the QDs in order to get the maximum overlap between the absorption band of the CdTe NNs and the emission band of the ZnSe QDs, which is a prerequisite for effective charge/energy transfer. The possibility of photoinduced charge transfer (PCT) and Förster resonance energy transfer (FRET) from the donor (QDs) to the acceptor (NNs) has been assessed. Very fast (less than 800 ps) PCT and FRET from QDs to NNs occur because the emission band of QDs overlaps with the absorption band of NNs. The calculated large value of the overlapping integral, J(λ) ∼4.5 × 10¹⁹M^-1cm^-1nm⁴, of the donor and the acceptor bands proves the feasibility of energy transfer. These findings suggest that the ZnSe QDs can exchange photoinduced energy with the CdTe NNs effectively over a wide distance in a CdTe-ZnSe nanohybrid.

Surface defect engineering of mesoporous Cu/ZnS nanocrystal-linked networks for improved visible-light photocatalytic hydrogen production

Cu-doped ZnS nanocrystal-linked mesoporous frameworks possessing suitable electronic energy levels, strong visible-light absorption and large porosity with a low defective surface show efficient photocatalytic H₂ evolution activity from water splitting.

The structural properties of silicon-doped DBrTBT/ZnSe solar cell materials: a theoretical study

A new molecular design for solar cell materials is reported for the silicon-doped 4,7-di(5-bromothiophen-2-yl)-2,1,3-benzothiadiazole adsorbed on ZnSe(100) and ZnSe(111) surfaces.

Simultaneous Bottom-Up Interfacial and Bulk Defect Passivation in Highly Efficient Planar Perovskite Solar Cells using Nonconjugated Small-Molecule Electrolytes

Recent perovskite solar cell (PSC) advances have pursued strategies for reducing interfacial energetic mismatches to mitigate energy losses, as well as to minimize interfacial and bulk defects and ion vacancies to maximize charge transfer. Here nonconjugated multi-zwitterionic small-molecule electrolytes (NSEs) are introduced, which act not only as charge-extracting layers for barrier-free charge collection at planar triple cation PSC cathodes but also passivate charged defects at the perovskite bulk/interface via a spontaneous bottom-up passivation effect. Implementing these synergistic properties affords NSE-based planar PSCs that deliver a remarkable power conversion efficiency of 21.18% with a maximum V_OC = 1.19 V, in combination with suppressed hysteresis and enhanced environmental, thermal, and light-soaking stability. Thus, this work demonstrates that the bottom-up, simultaneous interfacial and bulk trap passivation using NSE modifiers is a promising strategy to overcome outstanding issues impeding further PSC advances.

All-Inorganic CsPbBr3 Perovskite Solar Cells with 10.45% Efficiency by Evaporation-Assisted Deposition and Setting Intermediate Energy Levels

Nowadays, inorganic CsPbBr₃ perovskite is emerging as a promising candidate as a light-absorbing layer in photovoltaic devices due to its excellent photoelectric property and superior stability under humidity and thermal attacks in comparison with organic cation-based hybrid perovskites. However, the impure perovskite phase and severe interfacial charge recombination have limited the further improvement of device performance. In this work, a vapor-assisted solution technique was introduced to prepare a high-purity CsPbBr₃ film in a perovskite solar cell (PSC). To further reduce the electron-hole recombination and enhance charge extraction, we introduced the novel intermediate energy level of manganese sulfide (MnS) as a hole transport layer in CsPbBr₃ PSC. The as-optimized CsPbBr₃ PSC based on all-inorganic transport layers delivers a power conversion efficiency (PCE) of 10.45% in comparison with 8.16% for the device free of an intermediate layer, which is one of the highest PCEs achieved among the CsPbBr₃-based PSCs to date. Moreover, the optimized device retained 80% PCE of its initial efficiency over 90 days under 80% relative humidity at 85 °C, indicating an excellent environmental tolerance to boost the commercial application of low-cost, efficient, and stable all-inorganic PSCs.

Temperature Impact on Perovskite Solar Cells Under Operation

Perovskite solar cells (PSC) have emerged as a promising substitute for conventional silicon panels, showing the fastest power conversion efficiency evolution within the photovoltaic field, going from 3.8 % to 23.7 % in a few years. However, PSC thermal stability is still an obstacle to their commercialization. In this study, the temperature effect on mesoporous triple-cation perovskite solar cells with two different hole extraction materials-2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)-is assessed. The cells are exposed to thermal stress between -5 °C and 80 °C and their photovoltaic performance is monitored in situ to reproduce real operating conditions. At low temperatures, the devices present very stable values (average loss <5 %), but as the temperature increases significant decreases in the open circuit potential and short-circuit current are observed. X-ray diffraction shows no change in the perovskite crystal structure with temperature. However, electron scanning microscopy and X-ray photoelectron spectroscopy indicate that temperature has a great impact on the hole extraction layer. The cell performance loss is attributed to the evaporation of additives added to the hole extraction layer to enhance its conductivity. Although the decrease in power conversion efficiency at 80 °C is slightly higher for PTAA cells, spiro-OMeTAD cells present a higher irreversible loss of (21.6±2.3) % after thermal stress tests, whereas PTAA devices showed only a loss of (8.2±1.6) %.

Cerium-Oxide-Modified Anodes for Efficient and UV-Stable ZnO-Based Perovskite Solar Cells

CeO _x has been widely used in optoelectronic devices due to its special electronic and optical structure. Herein, CeO _x was directly doped into ZnO to successfully construct a ZnO/CeO _x electron transport material (ETM) used in perovskite solar cells (PSCs). The incorporation of CeO _x can regulate the chemical compatibility between ZnO and perovskite, unmatched energy levels, and poor UV stability, further enhancing the cell performance and stability of PSCs. As expected, the best efficiency of fabricated CH₃NH₃PbI₃-PSCs based on ZnO/CeO _x as the ETM was up to 19.5%. In contrast, the efficiency of PSCs with pure ZnO was 16.0%. Moreover, compared with PSCs based on ZnO, ZnO/CeO _x-based PSCs exhibited significantly enhanced moisture, and thermal and UV stability. These results point to the introduction of rare-earth oxides, which could accelerate the industrialization of PSCs.

Enhanced moisture stability of metal halide perovskite solar cells based on sulfur-oleylamine surface modification

As one of the most promising light-harvesting materials, perovskites have drawn tremendous attention for their unique advantages, such as high efficiency, low cost and facile fabrication compared with other photovoltaic materials. Nevertheless, poor moisture tolerance of the perovskites greatly hampers the operation of such devices and hinders their commercialization. Herein, we demonstrate a facile dipping treatment using sulfur-oleylamine solution for surface atomic modulation of perovskite films. Oleylammonium polysulfides (OPs) would be self-assembled on the etched perovskite film as an ultrathin outer layer. This layer could passivate the surface chemical activity of the outer perovskite layers. Moreover, the hydrophobic OPs significantly enhance moisture stability of such devices. As a result, the obtained device without encapsulation retains more than 70% of its initial power conversion efficiency (PCE) after 14 days of exposure to a relative humidity of 40 ± 10%.