First-Principles Study of Electron Injection and Defects at the TiO₂/CH₃NH₃PbI₃ Interface of Perovskite Solar Cells

Abstract

We investigated electron injection rates and vacancy defect properties by performing first-principles calculations on the interface of an anatase-TiO(001) and a tetragonal CHNHPbI(110) (MAPbI(110)). We found that the coupling matrix element between the lowest unoccupied molecular orbital of MAPbI and the TiO conduction band (CB) minimum is negligibly small, the indication being that electron-injection times for low-energy excited states are quite long (more than several tens of picoseconds). We also found that higher-lying CB states coupled more strongly; injection was expected to take place on a femtosecond time scale. Furthermore, we found that vacancy defects in the TiO layer produced undesired defect levels that caused hole traps and recombination centers. Whereas most of the vacancy defects in the MAPbI layer produced no additional states in the MAPbI gap, a Pb vacancy (V) at the interface created an energy level below the MAPbI CB edge and had a lower energy of formation than the V defect in bulk because of the interaction with the TiO surface.

Interfaces Between Graphene‐Related Materials and MAPbI3: Insights from First‐Principles

“…Furthermore, the charge transport layers in devices are usually mixed with the GRMs, which further complicates computational modeling. Ab initio calculations have been used to probe interfaces between GRMs/TiO 2 , MAPbI 3 /TiO 2 , and as discussed in this review MAPbI 3 /GRMs. However, a realistic description of the ternary interfaces between perovskites and mixed charge transport layers remains currently particularly demanding.…”

Review of First-Principles Studies of TiO2: Nanocluster, Bulk, and Material Interface

“…One major reason is the conduction band of TiO 2 is lower than that of the halide perovskite such as MAPbI 3 and MASnI 3 (MA = CH 3 NH 3 , methylammonium) [16,17]. Therefore, first-principles computational studies of TiO 2 /perovskite interfaces have been an emerging topic recently [16][17][18][19][20][21][22][23][24].…”

“…The defect properties at the TiO 2 /perovskite interface were also studied from first-principles calculations. In 2017, Haruyama et al reported the defect properties at the a TiO 2 (101)/tMAPbI 3 (110) interface using first-principles computational approach, in which anatase TiO 2 (001) was placed on the MAPbI 3 (110) plane [20]. They found that the vacancy defects in the TiO 2 layer create undesired defect levels within the bandgap, which serves as hole traps and recombination centers; while most of the vacancy defects in the MAPbI 3 layer produces no additional states, thus having no influence on the electron-hole separation rates.…”

“…To do so, increasing efforts are being made to synthesize TiO 2 -based materials heterostructures and/or composites that utilize the interfacial charge transfer mechanism to promote the separation rate of electron-hole pairs [11][12][13][14][15]. A high charge separation rate is beneficial not only for photocatalysts, but also for photovoltaic cells in which TiO 2 is often used as electron transport layers as they both use the separated electrons and holes [16][17][18][19][20][21][22][23][24].…”

Effects of Transition Metal Substituents on Interfacial and Electronic Structure of CH3NH3PbI3/TiO2 Interface: A First-Principles Comparative Study

“…Therefore, transition metal substituents in the TiO 2 layer are quite important and further characterizations are required to understand the effects of substituents in the CH 3 NH 3 PbI 3 /TiO 2 interface. Although the electronic properties of perovskite/ETL interface have been widely investigated by experiments and density-functional-theory (DFT) calculations [24,25,26,27,28,29,30,31], the existence of theoretical studies aiming to understand the fundamental role of the interfacial substituents is still rather scarce. In addition to the primary experiments, the first-principles DFT calculations are highly important to acquire further knowledge concerning the effects of transition metal substitution and contribute to new strategies for interface optimization.…”