Hydrogen Passivated Silicon Grain Boundaries Greatly Reduce Charge Recombination for Improved Silicon/Perovskite Tandem Solar Cell Performance: Time Domain Ab Initio Analysis

Abstract

By performing nonadiabatic molecular dynamics simulations, we demonstrate that grain boundaries (GBs) can induce the indirect-to-direct transition of the silicon band gap. However, missing a silicon atom creates an electron trap state in the GBs. Electron trapping by the silicon vacancy occurs on tens of picoseconds followed by recombination of the trapped electron and valence band hole on sub-100 ps, which operates parallel to recombination of the free electron and hole on a similar time scale. The recombination is greatly accelerated by 2 orders of magnitude compared to the GBs without a silicon vacancy. Hydrogen passivation eliminates the trap state and notably delays the charge recombination due to an increased band gap and a shortened coherence time, extending the excited-state lifetime to sub-10 ns.Our study provides an atomistic description of how charge recombination in the silicon can be efficiently reduced, suggesting a rational route to enhance silicon/perovskite tandem solar cells performance.

MAI Termination Favors Efficient Hole Extraction and Slow Charge Recombination at the MAPbI3/CuSCN Heterojunction

“…The quantum decoherence correction to FSSH is used in the electron–hole recombination simulation, − because the recombination time is much longer than the decoherence time. The decoherence time is computed by the second-order cumulant approximation of the optical response theory. , The approach has been applied successfully to study photoexcitation dynamics in a broad range of systems, including perovskites − and many other materials. − A detailed description of the theoretical methodology can be found in refs and .…”

Two-Dimensional Perovskite Capping Layer Simultaneously Improves the Charge Carriers’ Lifetime and Stability of MAPbI3 Perovskite: A Time-Domain Ab Initio Study

“…27 This approach has been applied to the study of photoexcitation charge dynamics for a variety of materials, 30−39 such as lead halide perovskites 30 −32,34 and their heterojunctions formed with other materials, 34,37,38 two-dimensional transition-metal dichalcogenides, 39 black phosphorus, 36 and silicon. 38 A detailed description of the NAMD methodology can be found in the literature. 40,41 Geometry optimization, adiabatic MD, and NA coupling are calculated using the Vienna ab initio simulation package (VASP).…”

“…Decoherence correction is needed because the decoherence time is significantly shorter than the electron–hole recombination time, which occurs over several nanoseconds in perovskites . This approach has been applied to the study of photoexcitation charge dynamics for a variety of materials, − such as lead halide perovskites − , and their heterojunctions formed with other materials, ,, two-dimensional transition-metal dichalcogenides, black phosphorus, and silicon . A detailed description of the NAMD methodology can be found in the literature. , …”

A Simple Solution to Trivial Crossings: A Stochastic State Tracking Approach

“…Nonadiabatic molecular dynamics (NA-MD) is a powerful method to study the dynamics of excited states, − including charge and energy transfer processes in various systems. In particular, quantum-classical trajectory surface hopping (TSH) algorithms, such as the Tully’s fewest switches surface hopping (FSSH), are the most widely used techniques due to their conceptual simplicity and computational efficiency that enable a straightforward use of the TSH-like algorithms in modeling of nonadiabatic dynamics (NAD) in complex systems. − The TSH-based NAD calculations rely on the classical path approximation (CPA), , according to which nuclei evolve classically, following the Newtonian equations of motion. Each trajectory evolves on a state-specific potential energy surface (PES).…”