Interpretation of inverted photocurrent transients in organic lead halide perovskite solar cells; proof of the field screening by mobile ions and determination of the space charge layer widths
Author(s)
Type
Journal Article
Abstract
In Methyl Ammonium Lead Iodide (MAPI) perovskite solar cells, screening of the built in
field by mobile ions has been proposed as part of the cause of the large hysteresis observed in
the current/voltage scans in many cells. We show that photocurrent transients measured
immediately (e.g. 100 μs) after a voltage step can provide direct evidence that this field
screening exists. Just after a step to forward bias, the photocurrent transients are reversed in
sign (i.e. inverted), and the magnitude of the inverted transients can be used to find an upper
bound on the width of the space charge layers adjacent to the electrodes. This in turn provides
a lower bound on the mobile charge concentration, which we find to be
1 x 10
17
/cm
3
. Using
a new photocurrent transient experiment, we show that the space charge layer thickness
remains approximately constant as a function of bias, as expected for mobile ions in a solid
electrolyte. We also discuss additional characteristics of the inverted photocurrent transients
that imply either an unusually stable deep trapping, or a photo effect on the mobile ion
conductivity.
field by mobile ions has been proposed as part of the cause of the large hysteresis observed in
the current/voltage scans in many cells. We show that photocurrent transients measured
immediately (e.g. 100 μs) after a voltage step can provide direct evidence that this field
screening exists. Just after a step to forward bias, the photocurrent transients are reversed in
sign (i.e. inverted), and the magnitude of the inverted transients can be used to find an upper
bound on the width of the space charge layers adjacent to the electrodes. This in turn provides
a lower bound on the mobile charge concentration, which we find to be
1 x 10
17
/cm
3
. Using
a new photocurrent transient experiment, we show that the space charge layer thickness
remains approximately constant as a function of bias, as expected for mobile ions in a solid
electrolyte. We also discuss additional characteristics of the inverted photocurrent transients
that imply either an unusually stable deep trapping, or a photo effect on the mobile ion
conductivity.
Date Issued
2016-12-21
Date Acceptance
2016-12-13
Citation
Energy & Environmental Science, 2016, 10, pp.192-204
ISSN
1754-5706
Publisher
Royal Society of Chemistry
Start Page
192
End Page
204
Journal / Book Title
Energy & Environmental Science
Volume
10
Copyright Statement
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
License URL
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (E
Engineering & Physical Science Research Council (E
Grant Number
EP/J002305/1
EP/H040218/1
n/a
Subjects
Science & Technology
Physical Sciences
Technology
Life Sciences & Biomedicine
Chemistry, Multidisciplinary
Energy & Fuels
Engineering, Chemical
Environmental Sciences
Chemistry
Engineering
Environmental Sciences & Ecology
ORGANOMETAL TRIHALIDE PEROVSKITE
ANOMALOUS HYSTERESIS
THIN-FILMS
EFFICIENT
MIGRATION
BEHAVIOR
MD Multidisciplinary
Energy
Publication Status
Published