Alleviating Interfacial Recombination of Heterojunction Electron Transport Layer via Oxygen Vacancy Engineering for Efficient Perovskite Solar Cells Over 23%

Electron transport layer(ETL)is pivotal to charge carrier transport for PSCs to reach the Shockley-Queisser limit.This study provides a fundamental understanding of heterojunction electron transport layers(ETLs)at the atomic level for stable and efficient perovskite solar cells(PSCs).The bilayer structure of an ETL composed of SnO_(2) on TiO_(2) was examined,revealing a critical factor limiting its potential to obtain efficient performance.Alteration of oxygen vacancies in the TiO_(2) underlayer via an annealing process is found to induce manipulated band offsets at the interface between the TiO_(2) and SnO_(2) layers.In-depth electronic investigations of the bilayer structure elucidate the importance of the electronic properties at the interface between the TiO_(2) and SnO_(2) layers.The apparent correlation in hysteresis phenomena,including current density-voltage(J-V)curves,appears as a function of the type of band alignment.Density functional theory calculations reveal the intimate relationship between oxygen vacancies,deep trap states,and charge transport efficiency at the interface between the TiO_(2) and SnO_(2) layers.The formation of cascade band alignment via control over the TiO_(2) underlayer enhances device performance and suppresses hysteresis.Optimal performance exhibits a power conversion efficiency(PCE)of 23.45%with an open-circuit voltage(V_(oc))of 1.184 V,showing better device stability under maximum power point tracking compared with a staggered bilayer under one-sun continuous illumination.

Interfacial defect engineering and photocatalysis properties of hBN/MX_(2)(M=Mo,W,and X=S,Se)heterostructures

Van der Waals(VDW)heterostructures have attracted significant research interest due to their tunable interfacial properties and potential applications in many areas such as electronics,optoelectronic,and heterocatalysis.In this work,the influences of interfacial defects on the electronic structures and photocatalytic properties of hBN/MX_(2)(M=Mo,W,and X=S,Se)are studied using density functional theory calculations.The results reveal that the band alignment of hBN/MX_(2) can be adjusted by introducing vacancies and atomic doping.The type-Ⅰband alignment of the host structure is maintained in the heterostructure with n-type doping in the hBN sublayer.Interestingly,the band alignment changed into the type-Ⅱheterostructrue due to V_(B) defect and p-type doping is introduced into the hBN sublayer.This can conduce to the separation of photo-generated electron-hole pairs at the interfaces,which is highly desired for heterostructure photocatalysis.In addition,two Z-type heterostructures including h BN(BeB)/MoS_(2),hBN(Be_(B))/MoSe_(2),and hBN(V_(N))/MoSe_(2)are achieved,showing the decreasing of band gap and ideal redox potential for water splitting.Our results reveal the possibility of engineering the interfacial and photocatalysis properties of hBN/MX_(2) heterostructures via interfacial defects.

Stability of Sn-Pb mixed organic–inorganic halide perovskite solar cells:Progress,challenges,and perspectives

The exploration of low bandgap perovskite material to approach Shockley-Queisser limit of photovoltaic device is of great significance,but it is still challenging.During the past few years,tin–lead(Sn-Pb)mixed perovskites with low bandgaps have been rapidly developed,and their single junction solar cells have reached power conversion efficiency(PCE)over 21%,which also makes them ideal candidate as low bandgap sub-cell for tandem device.Nevertheless,due to the incorporation of unstable Sn^(2+),the stability issue becomes the vital problem for the further development of Sn-Pb mixed perovskite solar cells(PSCs).In this review,we are dedicated to give a full view in current understanding on the stability issue of SnPb mixed perovskites and their PSCs.We begin with the demonstration on the origin of instability of Sn-Pb mixed perovskites,including oxidation of Sn^(2+),defects,and interfacial layer induced instability.Sequentially,the up-to-date developments on the stability improvement of Sn-Pb mixed perovskites and their PSCs is systematically reviewed,including composition engineering,additive engineering,and interfacial engineering.At last,the current challenges and future perspectives on the stability study of Sn-Pb mixed PSCs are discussed,which we hope could promote the further application of Sn-Pb mixed perovskites towards commercialization.

Fracture mechanics analysis on Smart-Cut~technology.Part 2:Effect of bonding flaws

In Part 2 of the paper on the Smart-Cut process, the effects of bonding flaws characterized by the size and internal pressure before and after splitting are studied by using fracture mechanics models. It is found that the bonding flaws with large size are prone to cause severe deviation of defect growth, leading to a non-transferred area of thin layer when splitting. In a practical Smart-Cut process where the internal pressure of bonding flaws is very small, large interfacial defects always promote defect growth in the splitting process. Meanwhile, increasing the internal pressure of the bonding flaws decreases the defect growth and its deviation before splitting. The mechanism of relaxation of stiffener constraint is proposed to clarify the effect of bonding flaws. Moreover, the progress of the splitting process is analyzed when bonding flaws are present. After splitting, those bonding flaws with large size and high internal pressure are vulnerable for the blistering of the thin film during high-temperature annealing.

Interfacial defective Ti^(3+) on Ti/TiO_(2) as visible-light responsive sites with promoted charge transfer and photocatalytic performance

Defect sites on oxide semiconductors play a crucial role in promoting photocatalytiperformance and mod-ulating the bandgap structure of photocatalysts.However,the role of interfacial coordinatively unsatu-rated defect sites between metal and oxide in photocatalysis is still under debate.So,we designed an experiment to probe the role of interfacial coordinatively unsaturated defect sites.In this work,a se-ries of Ti/TiO_(2) photocatalysts with varying concentrations of interfacial Ti^(3+)sites were prepared through an epitaxial growth method under hydrothermal conditions.Through experimental and computational investigations,the roles of interfacial defect sites were discussed in detail.On the one hand,the inter-facial coordinatively unsaturated Ti^(3+)sites could act as visible-light-responsive sites in photocatalytic reactions due to the overlap and hybridization of multiple electronic orbitals.On the other hand,the Ti/TiO_(2) interface exhibited a certain degree of metallic character near the Fermi level because of the par-tial delocalization and redistribution of electrons,facilitating the charge migration and separation across the metal-oxide interface.Consequently,the obtained Ti/TiO_(2) catalysts showed notably enhanced charge transfer efficiency and visible light photocatalytic activity compared to their pristine counterparts.This work may provide a new perspective to interfacial defect engineering in classic metal/oxide heterojunc-tion photocatalysts and figure a more precise direction to synthesize higher effective photocatalysts for environmental governance.

Deep insights into interface engineering by buffer layer for efficient perovskite solar cells: a firstprinciples study

Recent years have seen swift increase in the power conversion efficiency of perovskite solar cells(PSCs)Interface engineering is a promising route for further improving the performance of PSCs.Here we perform firstprinciples calculations to explore the effect of four candidate buffer materials(MACl,MAI,PbCl2and PbI2)on the electronic structures of the interface between MAPbI3absorber and TiO2.We find that MAX(X=Cl,I)as buffer layers will introduce a high electron barrier and enhance the electronhole recombination.Additionally,MAX does not passivate the surface states well.The conduction band minimum of PbI2is much lower than that of MAPbI3absorber,which significantly limits the band bending of the absorber and open-circuit voltage of solar cells.On the other side,suitable bandedge energy level positions,small lattice mismatch with TiO2surfaces,and excellent surface passivation make PbCl2a promising buffer material for absorber/electron-transport-layer interface engineering in PSCs.Our results in this work thus provide deep understanding on the effects of interface engineering with a buffer layer,which shall be useful for improving the performance of PSCs and related optoelectronics.