Round Robin Test Project

Article: Benchmarking Chemical Stability of Arbitrarily Mixed 3D Hybrid Halide Perovskites for Solar Cell Applications

Accurate and fast assessment of the intrinsic instability of mixed composition hybrid halide perovskite material is of vital importance for the development of perovskite solar cells. A longer lifetime close to current silicon based technology is a mandatory property for perovskite solar cells to reach commercial applications. The conventional method to evaluate the operational stability performance of perovskite solar cells relies on tracking maximum power efficiency on devices. However, this operational stability testing procedure requires a long measurement time, which is an inefficient procedure to screen the huge compositional space of mixed perovskites. Here, a thermal degradation protocol is shown for fast preliminary screening evaluation of the stability of any mixed 3D hybrid perovskite material. This stability assessment determines two independent parameters for stability quantification:

1. Degradation temperature (T_d)

2. Heat absorbed during degradation (Q_HAMDR)

Summary of the stability map of selected compositions of hybrid perovskite

An experimental entropic-like parameter can be derived addressing the relative stability for each mixed hybrid perovskite composition. In addition, a first principles theoretical approach (DFT) is described for the in silico search of optimal mixed composition perovskites. This experimental stability benchmarking protocol is able to signify several general rules of thumb to find enhanced stability trends in mixed composition perovskites prior to device assembly and conventional stability tests.

Round Robin Test Project

I am running a long term Round-Robin test to verify the inter-laboratory reproducibility (accuracy and precision) of this stability benchmarking protocol consisting of a controlled thermal degradation of perovskite material to obtain these two empirical figures of merit for stability quantification.

The equipment necessary to participate in this Round Robin Test is a Thermogravimetry/Differential Thermal Analyzer (TG-DTA) able to run the measurement under inert gas conditions (preferably He but N₂ could work too), alumina crucibles for the sample measurement, an agate mortar and pestle set, powder X-ray facility to check material purity and the reagents and solvents needed to synthesize hybrid perovskite (CsI, CsBr, MAI, MABr, FAI, FABr, PbI₂ and PbBr₂).

Scheme depicting the measurement of TG and DTA for hybrid perovskite material under a constant heating ramp

Goals

Amenable goal: To consolidate FAPbBr₃ as de facto standard to compare qualitatively the stability between mixed perovskites using only T_d as the straightforward figure of merit of the method.

Ambitious goal: A two-sigma level on accuracy/precision in two figures of merit evaluated at intralaboratory level is obtained and this relatively easy measurement can be consolidated as a standard protocol for pre-screening general stability of hybrid perovskites before conventional stability tests carried out in working devices.

Major Hints/Notes

1. We note that sample preparation is a key to obtain reproducible results and probably the method is equipment dependent. Please, check carefully section 3.3 in this Supporting Information File.

2. This study as announced is tentative in nature and major changes may be made in the final goals according to suggestions from potential collaborators.

3. Tentatively, pristine chemical compositions such as MAPbI₃, MAPbBr₃, FAPbI₃ and FAPbBr₃ would be analyzed but other compositions and conditions could be agreed depending on the number of participants.

4. The output of this study would be a publication in due time authored by all collaborators.

5. Updates related to this project will be done in this post.

6. Please contact me if you are interested in participating in this Round Robin inter-laboratory test with your TG-DTA equipment, if you need more information, inquiries or just want to make suggestions.

Two figure of merit defining stability of arbitrary composition hybrid perovskite

2019-05-01. UPDATE: a new TG-DTA equipment with horizontal tube furnace has been added to the equipments pool. A new set of benchmarking measurements is in progress.