Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for Photovoltaics
Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for Photovoltaics
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DOI：
10.1021/jacs.7b04981
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发表时间：
2017-08-16
影响因子：
15
通讯作者：
McGehee, Michael D.
中科院分区：
文献类型：
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作者：
Prasanna, Rohit;Gold-Parker, Aryeh;McGehee, Michael D.
组成AMX(3)的锡和碘化铅钙钛矿半导体，其中M是金属，X是卤化物，是高效低成本串联光伏的主要候选者，部分原因是它们具有可以通过成分替代在大范围内调节的带隙。我们通过实验确定了a位阳离子影响三维金属卤化物钙钛矿带隙的两种竞争机制。使用较小的a位阳离子可以以两种不同的方式扭曲钙钛矿晶格：通过倾斜MX6八面体或通过简单地各向同性收缩晶格。前者使带隙增大，后者使带隙减小。由于八面体倾斜，较大的甲脒被较小的铯部分取代后，碘化铅钙钛矿的带隙增加。比铅略小的锡钙钛矿则表现出相反的趋势：它们在碳取代时没有表现出八面体倾斜，而只是晶格收缩，导致带隙逐渐缩小。我们概述了一种策略，通过控制阳离子组成来系统地调整金属卤化物钙钛矿的带隙、价带和导带位置。利用这种策略，我们展示了太阳能电池可以在1040 nm的红外线中收集光，达到17.8%的稳定功率转换效率，这表明了全钙钛矿串联太阳能电池底部电池的改进前景。我们描述的阳离子基带隙调谐机制广泛适用于三维金属卤化物钙钛矿，并将有助于进一步开发用于光电应用的钙钛矿半导体。
Tin and lead iodide perovskite semiconductors of the composition AMX(3), where M is a metal and X is a halide, are leading candidates for high efficiency low cost tandem photovoltaics, in part because they have band gaps that can be tuned over a wide range by compositional substitution. We experimentally identify two competing mechanisms through which the A-site cation influences the band gap of 3D metal halide perovskites. Using a smaller A-site cation can distort the perovskite lattice in two distinct ways: by tilting the MX6 octahedra or by simply contracting the lattice isotropically. The former effect tends to raise the band gap, while the latter tends to decrease it. Lead iodide perovskites show an increase in band gap upon partial substitution of the larger formamidinium with the smaller cesium, due to octahedral tilting. Perovskites based on tin, which is slightly smaller than lead, show the opposite trend: they show no octahedral tilting upon Cs-substitution but only a contraction of the lattice, leading to progressive reduction of the band gap. We outline a strategy to systematically tune the band gap and valence and conduction band positions of metal halide perovskites through control of the cation composition. Using this strategy, we demonstrate solar cells that harvest light in the infrared up to 1040 nm, reaching a stabilized power conversion efficiency of 17.8%, showing promise for improvements of the bottom cell of all-perovskite tandem solar cells. The mechanisms of cation based band gap tuning we describe are broadly applicable to 3D metal halide perovskites and will be useful in further development of perovskite semiconductors for optoelectronic applications.