Interface Defect Density Research Articles

Nanoscale capacitance-voltage profiling of DC bias induced stress on a high-κ/SiO2/Si gate stack

We investigate DC bias stress effects on a HfOx/SiO2/p-Si gate stack using time-resolved scanning nonlinear dielectric microscopy. Our microscopy permits localized capacitance-voltage profiling and deep level transient spectroscopy on a particular area stressed prior to the measurement. We observed the increase of interface defect density and the drastic changes of local capacitance-voltage characteristics on the stressed area. Our numerical simulations explain that both fixed charges and interface defect density increased by the DC bias stress and caused the change of local characteristics. Because local capacitance-voltage characteristics is particularly important in device performance, time-resolved scanning nonlinear dielectric microscopy will be useful for the evaluation of local stress effects on miniaturized Si devices such as bias temperature instability.

Local capacitance-voltage profiling and high voltage stress effect study of SiO2/SiC structures by time-resolved scanning nonlinear dielectric microscopy

We investigate SiO2/SiC structures by a nanoscale capacitance-voltage (CV) profiling method based on time-resolved scanning nonlinear dielectric microscopy (tr-SNDM). Owing to the high sensitivity to the variation in the tip-sample capacitance, wide bandwidth of the measurement, and high flexibility of offline processing, tr-SNDM permits the more accurate acquisition of the microscopic CV characteristics localized below the scanning tip. We demonstrate that tr-SNDM based local CV profiling is able to distinguish the different features of untreated and nitrided SiO2/SiC structures and image intrinsic spatial non-uniformity of the interfaces. We also investigate the nanoscale impacts of high voltage stress on the SiO2/SiC structures. By inspecting the local CV characteristics under high voltage stress, we suggest that the interface defect density locally increases during the stress application.

Comprehensive device simulation of 23.36% efficient two-terminal perovskite-PbS CQD tandem solar cell for low-cost applications

The major losses that limit the efficiency of a single-junction solar cell are thermalization loss and transmission loss. Thus, to efficiently utilize the full solar spectrum and to mitigate these losses, tandem solar cells (TSC) have significantly impacted the photovoltaic (PV) landscape. In this context, the research on perovskite/silicon tandems is currently dominating the research community. The stability improvements of perovskite materials and mature fabrication techniques of silicon have underpinned the rapid progress of perovskite/silicon TSC. However, the low absorption coefficient and high module cost of the silicon are the tailbacks for the mass production of perovskite/silicon TSCs. Therefore, PV technology demands to explore some new materials other than Si to be used as absorber layer in the bottom cell. Thus, here in this work, to mitigate the aforementioned losses and to reduce cost, a 23.36% efficient two-terminal perovskite-PbS CQD monolithic tandem solar cell has been designed through comprehensive device simulations. Before analyzing the performance of the proposed TSC, the performance of perovskite top cells has been optimized in terms of variation in optical properties, thickness, and interface defect density under standalone conditions. Thereafter, filtered spectrum and associated integrated filtered power by the top cell at different perovskite thickness from 50 to 500 nm is obtained to conceive the presence of the top cell above the bottom cell with different perovskite thickness. The current matching by concurrently varying the thickness of both the top and bottom subcell has also been done to obtain the maximum deliverable tandem JSC for the device under consideration. The top/bottom subcell with current matched JSC of 16.68 mA cm−2/16.62 mA cm−2 showed the conversion efficiency of 14.60%/9.07% under tandem configuration with an optimized thickness of 143 nm/470 nm, where the top cell is simulated under AM1.5G spectrum, and bottom cell is exposed to the spectrum filtered by 143 nm thick top cell. Further, the voltages at equal current points are added together to generate tandem J–V characteristics. This work concludes a 23.36% efficient perovskite-PbS CQD tandem design with 1.79 V (VOC), 16.67 mA cm−2 (JSC) and 78.3% (FF). The perovskite-PbS CQD tandem device proposed in this work may pave the way for the development of high-efficiency tandem solar cells for low-cost applications.

Increased surface recombination in crystalline silicon under light soaking due to Cu contamination

Light-induced degradation (LID) can occur in crystalline silicon (Si) due to increased recombination in the bulk or at the surfaces. As an example, copper (Cu) is a contaminant that reportedly causes LID in the bulk of Si under illumination. In this article, we show that Cu contamination can also increase recombination at the surface under illumination using surface saturation current density ( J 0 ) analysis. More specifically, in the presence of Cu we observed that J 0 increased from 14 fA/cm 2 to 330 fA/cm 2 in SiO 2 passivated Float Zone (FZ) Si, and from 11 fA/cm 2 to 200 fA/cm 2 in corresponding Czochralski (Cz) Si after illumination under an LED lamp (0.6 Suns, 80 °C). In reference samples without Cu contamination, the J 0 was unaffected. These results demonstrate that a significant increase in surface recombination is possible without the presence of hydrogen. Furthermore, hydrogen was not seen to affect the Cu-induced surface degradation as similar experiments made with hydrogenated silicon nitride (SiN x :H) did not show further increase in J 0 . However, the timescale of the observed degradation was relatively fast (hours) indicating that Cu-induced surface degradation is a separate phenomenon from the earlier reported surface-related degradation. • Cu contamination leads to increased surface recombination in Si under light soaking. • The phenomenon occurs in FZ and Cz Si with both SiO 2 and SiN x :H passivation. • Surface saturation current density J 0 remained at 10–15 fA/cm 2 in uncontaminated Si. • J 0 increased to 330 fA/cm 2 in FZ Si and to 200 fA/cm 2 in Cz Si during light soaking. • An increase in interfacial defect density was observed in Cu-contaminated samples.

Perovskite Metal–Oxide–Semiconductor Structures for Interface Characterization (Adv. Mater. Interfaces 20/2021)

Perovskite MOS Structures In article number 2101004, José M. V. Cunha and co-workers demonstrate that AC measurements performed on metal–oxide–semiconductor devices (MOS) allow for the study of the density of interface defects and interface fixed oxide charges present in the electron transport layer/perovskite interface, allowing for the development of highly-efficient perovskite solar cells, which have several applications, e.g., build-integrated photovoltaics.

Photo-induced defects in MAPbBr3 single crystals

Single crystals of hybrid organic–inorganic halide perovskite have exhibited significantly good stability and a low trap density, leading to advantageous applications in optoelectronics. Even with recent development of high-quality perovskite single crystals, a defect analysis should be addressed to improve device performance in addition to understand the interaction between photo-generated carriers and defects. In this paper, we present a photo-induced defect characterization of CH3NH3PbBr3 (MAPbBr3) perovskite single crystals using an interpretation of photo-current and photo-capacitance measurement. The bulk and the interfacial defect densities of MAPbBr3 crystals with a gold electrode are examined by the characterization of photo-capacitive response under three different wavelengths of light. The transient photo-response of the single crystals reveals the occurrence of carrier trapping and a recombination process. The photo-response under the various light conditions provides a possible origin of defects in MAPbBr3 single crystals. Our comprehensive optoelectronic analysis provides the establishment of the link between the carrier transport and device performance depending on the illuminations. The fundamental understanding of photo-induced defects in perovskites can be helpful to realize the origin of electrical loss and develop highly efficient optoelectronic devices.

The optimization of CsPbIBr2 top sub-cells for the application in monolithic all-perovskite tandem solar cells

More and more attention has been paid to CsPbIBr2 material for perovskite solar cells (PSCs), owing to the trade-off between bandgap and stability. However, the reported maximum power conversion efficiency (PCE) of CsPbIBr2 PSCs is lag behind that of the congeners due to the serious interface recombination of charge carriers. In this work, the effects of interface defect density and interface band offset on the properties of CsPbIBr2 PSCs are investigated. It is found that the characteristic of the front electron transfer layer (ETL)/perovskite interface has a significant influence on the performance of PSCs than that of the back perovskite/hole transfer layer (HTL) interface. Additionally, a PCE of 15.05% with a high open-circuit voltage (VOC) of 1.54 V is obtained for the PSCs with FTO/ZnOS/CsPbIBr2/CuAlO2/Au structure. Finally, two-terminal monolithic all-perovskite double-junction tandem solar cells (TSCs) with the architecture of FTO/ZnOS/CsPbIBr2/CuAlO2/ITO/TiO2/MAPbI3/Spiro-MeOTAD/Au are constructed, and a maximum PCE of 27.4% (VOC of 2.60 V, JSC of 12.21 mA/cm2, and FF of 86.42%) is obtained for the TSCs with top and bottom absorber thicknesses of 600 nm and 500 nm respectively. Furthermore, four-terminal triple-junction TSCs are designed with silicon solar cells as bottom sub-cell, and a maximum PCE of 35.35% is achieved. These results will provide theoretical guidance for the fabrication of high performance TSCs.

Numerical modelling analysis of (FA)0.85Cs0.15Pb(I0.85 Br0.15)3: (FAPI)-based perovskite solar cell with different ETMs using solar capacitance simulator

Perovskite solar cells (PSCs) are becoming the backbone of global photovoltaic (PV) industry due to their low cost manufacturing and long-lasting stability. Organic and inorganic Perovskite materials have unique electronic and optical features like high absorption coefficient, adjustable band gap and solution-based production method. In this study, numerical investigations have been performed to design and propose guidelines for novel solar cell configurations using SCAPS-1D simulator. A perovskite material (FA)0.85Cs0.15Pb(I0.85 Br 0.15)3 has been chosen as active absorber because of its easy experimental synthesis and durability alongside Copper oxide (CuO) hole transport material (HTM). The device performance was optimized for various electron transport materials (ETMs) like TiO2, IGZO, WO3 and SnO2. A comparative study has been performed to investigate the most efficient device configuration. Necessary investigations which have considerable influences on the optimized device performance and power conversion efficiency (PCE) have been carried out which include the diffusion length, band gaps, interface defect densities, thicknesses of different structural layers and temperature. In the proposed Au/CuO/ FA0.85Cs0.15 Pb (I0.85Br0.15)3 /ETMs/FTO solar cell configurations, the comparative role of ETMs has been examined in which TiO2 and SnO2 have shown remarkable results due to their high electron affinity and tunable band gaps. As per standard device optimization process in the simulation software, the thickness of the perovskite absorber layer was found to be 0.40 μm, optimized thickness values of ETMs TiO2, IGZO, WO3 and SnO2, were found to be 0.065, 0.060, 0.070 and 0.070 μm respectively along with CuO-HTM layer of optimized thickness value of 1.035 μm. Critical investigations regarding the variation of electrical parameters open-circuit voltage (Voc), Short circuit current (Jsc), Fill Factor (FF%) and quantum efficiency (QE) against thickness, temperature, interface defect density, carrier mobility, density of states, carrier generation and recombination’s have been performed and reported for all Au/CuO/ FA0.85Cs0.15 Pb (I0.85Br0.15)3 /ETMs/FTO compositions. Current investigations may certainly prove to be useful for designing and fabrication of highly efficient and cheap PSCs.

Atomic-Scale Interface Modification Improves the Performance of Cu(In1-xGax)Se2/Zn(O,S) Heterojunction Solar Cells.

Cadmium-free buffer layers deposited by a dry vacuum process are mandatory for low-cost and environmentally friendly Cu(In1-xGax)Se2 (CIGS) photovoltaic in-line production. Zn(O,S) has been identified as an alternative to the chemical bath deposited CdS buffer layer, providing comparable power conversion efficiencies. Recently, a significant efficiency enhancement has been reported for sputtered Zn(O,S) buffers after an annealing treatment of the complete solar cell stack; the enhancement was attributed to interdiffusion at the CIGS/Zn(O,S) interface, resulting in wide-gap ZnSO4 islands formation and reduced interface defects. Here, we exclude interdiffusion or island formation at the absorber/buffer interface after annealing up to 200 °C using high-resolution scanning transmission electron microscopy (HR-STEM) and energy-dispersive X-ray spectroscopy (EDX). Interestingly, HR-STEM imaging reveals an epitaxial relationship between a part of the Zn(O,S) buffer layer grains and the CIGS grains induced by annealing at such a low temperature. This alteration of the CIGS/buffer interface is expected to lead to a lower density of interface defects, and could explain the efficiency enhancement observed upon annealing the solar cell stack, although other causes cannot be excluded.

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.

Effects of Mg Doping on Double Channel Layer Atmospheric Pressure-Plasma Enhanced Chemical Vapor Deposition Fabricated Amorphous InGaZnO Thin Film Transistors

Amorphous IGZO (a-IGZO) has been proved to be a suitable material for the channel layer in a thin film transistor, showing high mobility even in low temperature fabrication, device electrical characteristic exceeds a-Si or other metal oxide semiconductor materials. In this work, bottom gate top TFT is fabricated. With Atmosphere Pressure-PECVD (AP-PECVD), a-IGZO is deposited as device channel layer. A double channel layer is tested with Mg doping added in the bottom layer. This work focus on how the Mg doping concentration in the bottom layer affects device electrical characteristic. The result for best device characteristics is 5% Mg doping, showing highest mobility, lowest threshold voltage, and nearly 108 in Ion/Ioff. A suitable doping concentration can lower interface defect density and affect grain size, which both leads to a better device characteristics. However, device characteristics show sign of degradation with excess doping concentration.

Pyrenesulfonic Acid Sodium Salt for Effective Bottom‐Surface Passivation to Attain High Performance of Perovskite Solar Cells

In perovskite solar cells, not only defects on the top perovskite film surface seriously affect device performance, those buried in the bottom perovskite–electron‐transfer layer (ETL) interface damage carrier extraction, transport, and device efficiency as well. Herein, a novel double‐sided passivation strategy is designed using a single π‐conjugation‐induced 1‐pyrenesulfonic acid sodium salt (PyNa+). It is found that it effectively passivates top and bottom interface defects to render high device performance. The π‐conjugated pyrene‐containing sodium salt electronically contributes to the surface band edges and influences the carrier dynamics by passivating defects at both top hole‐transfer layer (HTL)–perovskite and bottom perovskite–ETL interfaces. The density functional theory (DFT) calculation confirms that the Pb cluster and I—Pb antisite defects can be effectively passivated by the O···Pb coordination and electrostatic interaction of PyNa+. The carrier lifetimes are prolonged, the interface defect density is effectively reduced as measured by space‐charge‐limited current (SCLC). Through the double layer passivation of PyNa+, the device delivers improved power conversion efficiencies of 21.22% relative to that of a reference perovskite, and enhanced stability with 85% of original efficiency after 1440 h in atmospheric environment. Double‐sided passivation provides a comprehensive strategy for high‐performance perovskite solar cells.

Study on Annealing Process of Aluminum Oxide Passivation Layer for PERC Solar Cells

In this study, Atomic Layer Deposition (ALD) equipment was used to deposit Al2O3 film on a p-type silicon wafer, trimethylaluminum (TMA) and H2O were used as precursor materials, and then the post-annealing process was conducted under atmospheric pressure. The Al2O3 films annealed at different temperatures between 200–500 °C were compared to ascertain the effect of passivation films and to confirm the changes in film structure and thickness before and after annealing through TEM images. Furthermore, the negative fixed charge and interface defect density were analyzed using the C-V measurement method. Photo-induced carrier generation was used to measure the effective minority carrier lifetime, the implied open-circuit voltage, and the effective surface recombination velocity of the film. The carrier lifetime was found to be the longest (2181.7 μs) for Al2O3/Si post-annealed at 400 °C. Finally, with the use of VHF (40.68 MHz) plasma-enhanced chemical vapor deposition (PECVD) equipment, a silicon nitride (SiNx) film was plated as an anti-reflection layer over the front side of the wafer and as a capping layer on the back to realize a passivated emitter and rear contact (PERC) solar cell with optimal efficiency up to 21.54%.

Status of Al2O3/TiO2‐Based Antireflection and Surface Passivation for Silicon Solar Cells

Inhibiting charge recombination effectively by surface passivation is very important for high‐efficiency silicon solar cells. With the emergence of passivated emitter and rear cells (PERCs), which surpass conventional solar cells, the need for a novel passivation scheme is increasing. Passivation layer stacks using negatively charged Al2O3 have been applied successfully to realize high‐efficiency PERC solar cells. Herein, the developments of surface passivation by Al2O3/TiO2‐based layers are reviewed. The topics range from synthesis methods and optical properties as antireflection coatings to the electrical properties related to the material, interface, and passivation quality. Ultrathin Al2O3/TiO2‐based layers generally feature a combination of field‐effect passivation by negative fixed charges, a low interface defect density, and adequate humidity stability. Among the various deposition methods, atomic layer deposition is focused on, which can form dual layers and nanolaminates. How the features of atomic‐layer‐deposited Al2O3/TiO2‐based layers can be utilized for interface engineering and tailoring the properties of surface passivation schemes is discussed.

Optimal design and photovoltaic performance of eco friendly, stable and efficient perovskite solar cell

In this study, we have investigated a lead-free perovskite solar cell with Two-Dimensional (2-D) electron and hole transport materials using device simulation software. We have analyzed the characteristics of the solar cell and quantum efficiency at the illumination of light and measured the output performance parameters. We have varied device parameters, such as absorber thickness, absorber doping concentration, and defect density in the absorber layer, to get the optimized values of the solar cell module . We have also considered the effect of interface layer defect density and temperature variation factors. Simulation results showcase a short circuit current density ( Jsc ) of 27.3 mA/cm 2 , open-circuit voltage ( Voc ) of 0.96 V, fill-factor ( FF ) of 87.62%, and power conversion efficiency ( PCE ) of 22.17%. The high quantum efficiency ( QE) of 98% in the visible region is due to the material's high absorbance with our proposed perovskite solar cell (PSC). Finally, we compared our proposed PSC with other solar cells to state the efficiency of the perovskite material used in our cell module. This work provides a route towards the development of eco-friendly and stable perovskite solar cells. • In this study, with optimized parameters of proposed architecture, we have achieved 22.17% power conversion efficiency and 98% Quantum efficiency for perovskite solar cell. • Various factors affecting the cell's performance like thickness of absorber layer, absorber's doping concentration, absorber's defect density, absorber/ETL interface defect density, operating temperature, and by using different absorber material have been rigorously investigated. • We compared our proposed PSC with other solar cells with different absorber materials for comparative analysis.

Highly efficient Cesium Titanium (IV) Bromide perovskite solar cell and its point defect investigation: A computational study

Lead-free, halide-based perovskites are drawing appreciable attention for solar cell applications due to the non-toxic nature and stable performance in ambient environment. In this study, we investigated different facets of a Cesium Titanium (IV) Bromide (Cs 2 TiBr 6 ) perovskite solar cell (PSC) with ZnO and MoO 3 as charge transport materials. Upon numerical optimization of perovskite layer thickness, its defect density , and the interface defect density, we propose a highly efficient, practically realizable PSC with a power conversion efficiency of 18.15%. Besides, we investigated different point defects in Cs 2 TiBr 6 and the effect of their electronic band positions on the PSC performance. It is found that for Cs 2 TiBr 6 based PSC applications, the material processing of Cs 2 TiBr 6 is a crucial aspect and the PSC may underperform for deep defect states (0.2 eV ~ 1.6 eV) with defect density over 10 15 cm −3 . In addition, we analyzed different back contact materials and found that carbon-based back contact can be a low-cost solution to gold for Cs 2 TiBr 6 PSCs. • A Cesium Titanium (IV) Bromide (Cs 2 TiBr 6 ) based perovskite solar cell with FTO/ZnO/Cs 2 TiBr 6 /MoO 3 /Au structure is proposed. • An optimum power conversion efficiency (PCE) of 18.15% is achieved. • Investigation on possible point defects in Cs 2 TiBr 6 and their electronic band position's effect on the PSC performance. • For deep defect state (0.2 eV ~ 1.6 eV) and defect density over 10 15 cm −3 , the PSC tends to underperform. • Carbon-based back contact can be a possible low cost replacement of gold for Cs 2 TiBr 6 PSCs.

A SCAPS simulation investigation of non-toxic MAGeI3-on-Si tandem solar device utilizing monolithically integrated (2-T) and mechanically stacked (4-T) configurations

In this study, solar cell capacitance simulator (SCAPS) was utilized to investigate a tandem solar device with Methyl-ammonium germanium iodide (MAGeI3), an organic perovskite, as top cell active layer, and crystalline silicon (c-Si) as the bottom cell. Validation studies were done against established single-junction device structures including MAPbI3 and c-Si. Our simulation-based results showcase a robust congruence with experimental data, with obtained power conversion efficiency (PCE) values of 20.19%, and 23.01% for MAPbI3 and c-Si based single-junction devices, respectively. For the thesis of this work, both four-terminal (4-T) and two terminal (2-T) perovskite-on-silicon tandem architectures were investigated. Our numerical simulation for the monolithic stacked 2-T tandem structure of MAGeI3-on-c-Si produced a PCE of 28.71 %, while a PCE of 32.2 % was obtained for the standard MAPbI3-on-c-Si. For the current matching condition in the 2-T tandem devices, the optimum thickness of MAGeI3 and MAPbI3 were found to be 626 nm and 223 nm respectively. For the mechanically stacked 4-T configurations, MAGeI3-on-c-Si and MAPbI3-on-c-Si produced PCE values of 29.85 % and 33.67%, respectively, with optimum top cell absorber thickness values of 1.7 µm and 1.4 µm, respectively. Each device architecture was optimised by carrying out extensive studies including modulations in absorber thickness, bulk defect density, interfacial defect density, and back contact metal work function. Our in-depth analyses highlight a remarkable potential for MAGeI3 to be utilized as the top cell of a perovskite-on-silicon solar device, boasting high efficiency and intrinsic non-toxicity.

Al‐neal Degrades Al2O3 Passivation of Silicon Surface

Atomic layer deposited (ALD) aluminum oxide (Al2O3) has emerged as a useful material for silicon devices due to its capability for effective surface passivation and ability to generate p+ region underneath the oxide as active or passive component in semiconductor devices. However, it is uncertain how Al2O3 films tolerate the so‐called Al‐neal treatment that is a necessary process step in devices that also contain silicon dioxide (SiO2) passivation layers. Herein, it is reported that the Al‐neal process is harmful for the passivation performance of Al2O3 causing over eightfold increase in surface recombination velocity (SRV) (from 0.9 to 7.3 cm s−1). Interestingly, it is also observed that the stage at which the so‐called activation of Al2O3 passivation is performed impacts the final degradation strength. The best result is obtained when the activation step is done at the end of the process together with the Al‐neal thermal treatment, which results in SRV of 1.7 cm s−1. The results correlate well with the measured interface defect density, indicating that the Al‐neal affects defects at the Si/SiO x /Al2O3 interface. The root causes for the defect reactions are discussed and possible reasons for the observed phenomena are suggested.

Phosphoric acid-peroxide mixture surface preparation for the improvement of InGaAs channel characteristics

InGaAs is a potential candidate for a next-generation channel material of complementary metal-oxide-semiconductor devices based on its excellent electron mobility. In this study, the surface behaviors of the InGaAs after treatments in H3PO4/H2O2/H2O and HNO3/H2O2/H2O mixtures were investigated and compared with that after treatment in a HCl/H2O2/H2O mixture. Although the presence of Cl− in an acidic solution suppressed the overall etching reaction and material loss of the InGaAs surface, Cl− induced the roughening of the InGaAs surface. The smallest InGaAs/Al2O3 interface charge trap density was observed when the InGaAs surface was prepared in the H3PO4/H2O2/H2O solution. It was also confirmed that the H3PO4/H2O2/H2O-treated InGaAs surface had the highest electron mobility among the samples and the lowest interfacial defect density, such as arsenic vacancies and antisites. Finally, it was concluded that surface preparation of InGaAs with H3PO4/H2O2/H2O effectively improved the interfacial electrical properties at the metal-oxide-InGaAs semiconductor by successfully minimizing surface roughening and the interfacial defect density compared to a well-known HCl/H2O2/H2O solution process.

Device simulations of electron-transfer-layer-free perovskite solar cells focused on absorber/hole transfer-layer interface

In this paper, we report a study of electron-transfer-layer (ETL)-free perovskite solar cells, which included the structure of the fluorine-doped tin oxide/absorber/hole transfer-layer (HTL)/contact. Interface defect layers were introduced at the absorber interfaces to take the effect of interface defect densities into account. The simulations in this work were performed using solar cell capacitance-simulator (SCAPS-1D) software based on recent experimental and theoretical data. Along with the analysis and optimization of the thickness and defect density, special attention was paid to the effect of the energy band offset (BO) of the absorber/HTL interface and the effect of carrier mobility in the HTL on the performance of the solar cells. The optimum thickness for the absorber was 500 nm. The energy BO of the absorber/HTL interface significantly affected the charge-transport properties of the device. A BO of −0.05 eV to 0.2 eV was determined to be optimum to establish effective carrier transport. However, the tradeoff between the BO of the absorber/HTL interface and carrier mobility was found to be crucial to achieving high performance. The power conversion efficiency increased from 13.83% to up to 19.58% for HTLs with carrier mobilities of 5 × 10−6 cm2 V−1s−1 and 2 cm2 V−1s−1, respectively. Our investigations and findings will support the understanding of carrier transport mechanisms in ETL-free perovskite solar cells and the material development and selection of such devices.