Quantitative determination of Absolute Crystallinity and Texture of Perovskite Absorber Layer

Christopher Tassone^a, Michael Toney^a, Kevin Stone^a, Joey Luther^b, Joseph Berry^b

^aSLAC, 2575 Sand Hill Rd, Menlo Park , 94025, United States

^bNREL, 16253 Denver West Parkway, Golden, 80401, United States

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Oral, Christopher Tassone, presentation 106
Publication date: 5th February 2015

During the last two years, a stir of excitement has been created around lead-based organic-inorganic halide perovskite materials used as solar absorber materials. While efficiencies have increased at an amazing rate, there have not been a commensurate amount of systematic studies as to what precisely is responsible for increased efficiencies in the perovskite absorber layer. While the community at large has the tools available to characterize the electronic properties of these materials, similar tools for evaluating the morphology of the perovskite layer have been under developed. Here we present a methodology for characterizing the absolute crystallinity as well as the crystalline texture of each layer on fully functional perovskite solar cells. We find that, for devices we have characterized, the perovskite layer is has a significant amorphous fraction, exceeding 30-40%, while still maintaining power conversion efficiencies >12%. Furthermore, we find that the degree of crystallinity is not the primary factor determining the power conversion efficiency of the devices, as devices with identical degrees of crystallinity as well as similar crystalline texture show efficiencies which can range over an order of magnitude. We use a combination of spectroscopic ellipsometry and cross sectional TEM to understand how the morphology contributes to these efficiency differences, given that with respect to the degree of crystallinity and texture of the crystallites, these absorber layers are nearly identical. With these initial studies we intend to demonstrate what aspects of the morphology are critical to device performance and which negligibly contribute, in order to begin a discussion about what the design rules are for perovskite based photovoltaics within the perovskite community.

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