Optimization of electron selective layer and perovskite crystallization for efficient outdoor and indoor light harvesting in graphite-based perovskite solar cells
Simone Mastroianni a b, Lukas Wagner a, Lakshmi S. Subramaniam a, Sijo Chacko a, Kübra Yasaroglu c, Wolfram Kwapil a, Laura D. Mundt a, Martin .C. Schubert a, Thomas Kroyer a, Andreas Hinsch a
a Fraunhofer Institute for Solar Energy Systems ISE, Germany, Heidenhofstraße, 2, Freiburg im Breisgau, Germany
b University of Freiburg, Freiburg Materials Research Center (FMF), Stefan-Meier-Straße 21, Freiburg, 79104, Germany
c University of Strasbourg, France., Strasbourg, France
NIPHO
Proceedings of International Conference on Perovskite Thin Film Photovoltaics, Photonics and Optoelectronics (ABXPV18PEROPTO)
Perovskite Thin Film Photovoltaics (ABXPV18). 27-28 Feb
Rennes, France, 2018 February 27th - March 1st
Organizer: Jacky Even
Oral, Simone Mastroianni, presentation 077
DOI: https://doi.org/10.29363/nanoge.abxpvperopto.2018.077
Publication date: 11th December 2017

Solar cells for low light harvesting are acquiring in the recent years an increasing interest for their commercial application in the market of Electronic and Product Integrated Photovoltaics (EIPV and PIPV). The solar technology based on perovskite crystals (PSCs) has a huge potential in this field.
In this work, we show that, for low light application, the reduction of electron recombination at the front contact and improved crystal quality are very crucial. Thus, a 2-fold optimization of the monolithic carbon-graphite based PSC used in this study is performed to achieve low non-radiative recombination and, hence, high VOC and efficiency under both full Sun and indoor light conditions:

1. Four different up-scalable electron selective layer (ETS) processes (sputtering, spray pyrolysis, screen-printing and atomic layer deposition) have been investigated through Dark Lock-In Thermography (DLIT) and optimized to achieve a pin-hole/defect free layer and reduced electron-hole recombination. With a spatial resolution < 100 μm, the DLIT analysis (vs. applied voltage) allows the determination of shunts in the layer. Furthermore, shunts can be distinguished into linear (ohmic) and non-linear through plotting the local I-V curve. Transmittance, SEM, AFM, XRD and ellipsometry support the whole analysis. Among the investigated ESLs, the PSCs fabricated with the c-TiO2 ALD-processed ESL showed the maximized VOC.

2. The high quality of the perovskite crystals into the porous structure of the carbon-graphite based PSC is achieved by a molten-salt based MAPbI3 precursor solution. This approach allows a dense pore filling (demonstrated by SEM and EDX maps) and a very fast charge transport through the porous layers (analysed by JSC, VOC and photoluminescence transients). Thereby, a stabilized photovoltage as high as 1 V is a reached, which is the highest for monolithic hole-transport-layer (HTL) free MAPbI3-based devices. We measured a stabilized PCE of 13.8% under 1 Sun and we report the certified stabilized efficiency of 12.6 %.

Following these two optimizations, the resulting high-efficient and low-cost HTL-free PSC is measured under low light intensity as well as under compact fluorescent lamp (CFL) and light-emitting diode (LED) illumination.

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