Investigation of Perovskite Solar Cells Employing Chemical Vapor Deposited Methylammonium Bismuth Iodide Layers
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.513
Investigation of Perovskite Solar Cells Employing Chemical Vapor Deposited Methylammonium Bismuth Iodide Layers Dominik Stümmler1, Simon Sanders1, Pascal Pfeiffer1, Noah Wickel1, Gintautas Simkus1,2, Michael Heuken1,2, Peter K. Baumann3, Andrei Vescan1, Holger Kalisch1 1
Compound Semiconductor Technology, RWTH Aachen University, Sommerfeldstr. 18, 52074 Aachen, Germany. 2
AIXTRON SE, Dornkaulstr. 2, 52134 Herzogenrath, Germany.
3
APEVA SE, Dornkaulstr. 2, 52134 Herzogenrath, Germany.
ABSTRACT Although Pb-based perovskite solar cells already achieve power conversion efficiencies (PCE) beyond 20 %, the use of toxic Pb is causing considerable environmental concern. As a consequence, a variety of alternative cations have been investigated to replace Pb 2+ in the perovskite structure. Methylammonium bismuth iodide (MA3Bi2I9, MBI) has shown promising results for environmentally benign and chemically stable devices. While the PCE of MBIbased solar cells are still comparably low, structural improvements have been made by using chemical vapor deposition (CVD). CVD allows for the well-controlled formation of coherent and dense MBI layers in contrast to solution-processing. In this work, CVD as a possible MBI fabrication method for efficient and size-scalable solar cells is discussed. The precursors MA iodide (MAI) and Bi iodide (BiI3) are deposited in an alternating deposition process forming the desired MBI perovskite on the heated substrate. Substrate temperatures as well as deposition times of each precursor are varied with the aim of forming coherent and dense MBI layers. Optimized films are further processed to solar cell prototypes and compared with solution-processed reference devices. The results reveal that CVD possesses great potential to enable the manufacture of MBI photovoltaic (PV) devices processed in a solvent-free environment.
INTRODUCTION Perovskite solar cells have become a prominent subject in photovoltaic (PV) research because of a rapid development of PCE figures. Benchmark devices reach PCE significantly >20 % [1]. For the widely used organo lead halide perovskites, solution-
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based (e.g. spin-coating) as well as vapor phase deposition have been demonstrated [2]. Recently, less toxic replacements for Pb and solvent-free processes have come into focus to overcome toxicity issues [3]. In this context, replacing Pb with less toxic Bi showed superior stability [4]. While lifetime improved strongly, PCE figures are still rather low, rarely exceeding the value of 1 % [5]. Solution-processing of MBI leads to films with poor substrate coverage, small crystal grains, deteriorated electronic properties and PV performance [6]. Efforts to optimize MBI solar cells are therefore mainly focused
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