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Overcoming the Photovoltage Plateau in Large Bandgap Perovskite Photovoltaics Adharsh Rajagopal, Ryan J Stoddard, Sae Byeok Jo, Hugh W. Hillhouse, and Alex K.-Y. Jen Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b01480 • Publication Date (Web): 07 May 2018 Downloaded from http://pubs.acs.org on May 7, 2018
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Nano Letters
Overcoming the Photovoltage Plateau in Large Bandgap Perovskite Photovoltaics Adharsh Rajagopal,1 Ryan J. Stoddard,2 Sae Byeok Jo,1 Hugh W. Hillhouse,2*and Alex K.-Y. Jen1,3,4* 1
Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195-2120, USA 2
Department of Chemical Engineering, Molecular Engineering and Sciences Institute, University of Washington, Seattle, WA 98195-1750, USA 3
Department of Materials Science & Engineering, City University of Hong Kong, Kowloon, Hong Kong 4
Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong
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Abstract: Development of large bandgap (1.80-1.85 eV Eg) perovskite is crucial for perovskite-perovskite tandem solar cells. However, the performance of 1.80-1.85 eV Eg perovskite solar cells (PVKSCs) are significantly lagging their counterparts in the 1.60-1.75 eV Eg range. This is because the photovoltage (Voc) does not proportionally increase with Eg due to lower optoelectronic quality of conventional (MA,FA,Cs)Pb(I,Br)3 and results in a photovoltage plateau (Voc limited to 80% of the theoretical limit for ~1.8 eV Eg). Here, we incorporate phenylethylammonium (PEA) in a mixed-halide perovskite composition to solve the inherent material-level challenges in 1.80-1.85 eV Eg perovskites. The amount of PEA incorporation governs the topography and optoelectronic properties of resultant films. Detailed structural and spectroscopic characterization reveal the characteristic trends in crystalline size, orientation, and charge carrier recombination dynamics and rationalize the origin of improved material quality with higher luminescence. With careful interface optimization, the improved material characteristics were translated to devices and Voc values of 1.30-1.35 V were achieved, which correspond to 85-87% of the theoretical limit. Using an optimal amount of PEA incorporation to balance the increase in Voc and the decrease in charge collection, a highest power conversion efficiency of 12.2% was realized. Our results clearly overcome the photovoltage plateau in the 1.80-1.85 eV Eg range and represent the highest Voc achieved for mixed-halide PVKSCs. This study provides widely translatable insights, an important breakthrough, and a promising platform for next-generation perovskite tandems.
Keywords: Tandem solar cell, optoelectronic quality, 2D-3D perovskite, charge recombination dynamics, mixed-halide phase segregation, open-circuit voltage bottleneck
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Nano Letters
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Nano Letters
Organic-inorganic hybrid perovskites are structurally and functionally versatile materials, brought to prominence because of their exceptional optoelectronic attributes for enabling next generation photovoltaics (PVs).1–3 A rapidly advancing research community has led to an unprecedented growth of hybrid perovskites-based PVs, achieving a power conversion efficiency (PCE) record of 22.7%.4,5 Progression in PCE for perovskite solar cells (PVKSCs) so far have transpired because of advancements on multiple fronts such as formulation of perovskite composition and processing approaches, design of interfaces, and fabrication of single junction device stacks, all primarily based on 1.6 eV bandgap (Eg) perovskites.6–8 To improve the PCE of PVKSCs past the single-junction Shockley-Queisser (SQ) limit, it is of increasing importance to develop perovskite device stacks with bandgaps tailored for construction of multi-junction (tandem) solar cells.9,10 The two-terminal (2-T) PVK-PVK tandem configuration particularly stands out among different choices because of their potential for having the least-energy intensive processing and the lowest energy payback time.11 The lowest Eg currently achieved with perovskites is ~1.2 eV and it ideally needs to be paired with ~1.8 eV large Eg perovskite to minimize the current matching loss and maximize the potential of 2-T PVK-PVK tandems.9,10 Succeeding the initial work by Eperon et al.,12 we recently advanced the PCE record to 18.5% for 2-T tandem using 1.2 eV and 1.8 eV Eg perovskite absorbers.13 This PCE significantly lags the 23.6% record achieved for 2-T Si-PVK tandems14 and is far below the practically realizable valuation ~35%. Analyses of optoelectronic losses in 2-T PVK-PVK tandems reveal that the low open-circuit voltage (Voc) in 1.8 eV Eg perovskite subcell is currently the major performance constraint.9,10,13 Large bandgaps are commonly realized using mixed-halide (I/Br) perovskite alloys, represented by a general formula APb(I1-yBry)3; 0
