Title: Solution-Processed BiI ₃ Films with 1.1 eV Quasi-Fermi Level Splitting: The Role of Water, Temperature, and Solvent during Processing

Abstract

Here, we present a mechanistic explanation of the BiI₃ film formation process and an analysis of the critical factors in preparing high-quality solution-processed BiI₃ films. We find that complexation with Lewis bases, relative humidity, and temperature are important factors during solvent vapor annealing (SVA) of films. During SVA, water vapor and higher temperatures limit the formation of the BiI₃–dimethylformamide coordination complex. SVA with an optimized water content and temperature produces films with 300–500 nm grains. Films that formed solvent coordination compounds at lower temperatures showed preferential crystal orientation after solvent removal, and we elucidate its implications for carrier transport. Addition of dimethyl sulfoxide to highly concentrated tetrahydrofuran–BiI₃ inks prevents film cracking after spin-coating. We have measured a quasi-Fermi level splitting of 1.1 eV and a diffusion length of 70 nm from films processed with optimal temperature and humidity. The best device produced by optimized SVA has a power conversion efficiency of 0.5%, I_sc of ~4 mA/cm², and V_OC of ~400 mV. The low photocurrent and voltage we attribute to the low diffusion length and the unfavorable band alignment between the absorber and the adjacent transport layers. The deep understanding of the relationship between morphology/crystal structure and optoelectronic properties gained frommore » this work paves the way for future optimization of BiI₃-based solar cells.« less

Authors:

Williamson, B. Wesley ^[1]; Eickemeyer, Felix T.  ^[1];

• Search DOE PAGES for author "Eickemeyer, Felix T."
• Search DOE PAGES for ORCID "0000-0003-0855-9944"

Hillhouse, Hugh W.  ^[1]

• Search DOE PAGES for author "Hillhouse, Hugh W."
• Search DOE PAGES for ORCID "0000-0003-2069-7899"

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+ Show Author Affiliations

1. Department of Chemical Engineering, Clean Energy Institute, and Molecular Engineering & Sciences Institute, University of Washington, Seattle, Washington 98105, United States

Publication Date:

Fri Oct 05 00:00:00 EDT 2018

Research Org.:

Univ. of Washington, Seattle, WA (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office

OSTI Identifier:

1476381

Alternate Identifier(s):

OSTI ID: 1480260

Grant/Contract Number:  

EE0006710

Resource Type:

Published Article

Journal Name:

ACS Omega

Additional Journal Information:

Journal Name: ACS Omega Journal Volume: 3 Journal Issue: 10; Journal ID: ISSN 2470-1343

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Coating materials; Crystal structure; Electron microscopy; Electronic structure; Energy level; Heat treatment; Photovoltaics; Solvation; Surface structure; Thermal properties; Water vapor