From Femtoseconds to Gigaseconds: The SolDeg Platform for the Performance Degradation Analysis of Silicon Heterojunction Solar Cells

Davis Unruh, Reza Vatan Meidanshahi, Chase Hansen, Salman Manzoor, Mariana I. Bertoni, Stephen M. Goodnick, Gergely T. Zimanyi

Research output: Contribution to journalArticlepeer-review

Abstract

Heterojunction Si solar cells exhibit notable performance degradation. We modeled this degradation by electronic defects getting generated by thermal activation across energy barriers over time. To analyze the physics of this degradation, we developed the SolDeg platform to simulate the dynamics of electronic defect generation. First, femtosecond molecular dynamics simulations were performed to create a-Si/c-Si stacks, using the machine learning-based Gaussian approximation potential. Second, we created shocked clusters by a cluster blaster method. Third, the shocked clusters were analyzed to identify which of them supported electronic defects. Fourth, the distribution of energy barriers that control the generation of these electronic defects was determined. Fifth, an accelerated Monte Carlo method was developed to simulate the thermally activated time-dependent defect generation across the barriers. Our main conclusions are as follows. (1) The degradation of a-Si/c-Si heterojunction solar cells via defect generation is controlled by a broad distribution of energy barriers. (2) We developed the SolDeg platform to track the microscopic dynamics of defect generation across this wide barrier distribution and determined the time-dependent defect density N(t) from femtoseconds to gigaseconds, over 24 orders of magnitude in time. (3) We have shown that a stretched exponential analytical form can successfully describe the defect generation N(t) over at least 10 orders of magnitude in time. (4) We found that in relative terms, Voc degrades at a rate of 0.2%/year over the first year, slowing with advancing time. (5) We developed the time correspondence curve to calibrate and validate the accelerated testing of solar cells. We found a compellingly simple scaling relationship between accelerated and normal times tnormal ∝ taccel T(accel)/T(normal). (6) We also carried out experimental studies of defect generation in a-Si:H/c-Si stacks. We found a relatively high degradation rate at early times that slowed considerably at longer time scales.

Original languageEnglish (US)
Pages (from-to)32424-32434
Number of pages11
JournalACS Applied Materials and Interfaces
Volume13
Issue number27
DOIs
StatePublished - Jul 14 2021

Keywords

  • amorphous silicon
  • density functional theory
  • interface defects
  • molecular dynamics
  • Monte Carlo
  • silicon heterojunctions
  • solar cells

ASJC Scopus subject areas

  • Materials Science(all)

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