We investigate the electronic structure of solution-processed perovskite solar cells using temperature-dependent electroabsorption (EA) spectroscopy. Simultaneous measurements of absorption and electromodulated spectra of semitransparent methylammonium lead iodide solar cells facilitate a direct comparison of the specific features. The EA spectra can be transformed to peak-like line shapes utilizing an approach based on the Kramers–Kronig relations. The resulting peak positions correspond well to the discrete excitonic—rather than the continuum—contribution of the absorption spectra derived from generalized Elliott fits. This indicates the excitonic nature of the observed EA resonance and is found to be consistent over the whole temperature range investigated (from T = 10 K up to room temperature). To further confirm these findings, a line shape analysis of the measured EA spectra was performed. The best agreement was achieved using a first-derivative-like functional form which is expected for excitonic systems and supports the conclusion of an excitonic optical transition. Exciton binding energies EB are estimated for the orthorhombic and tetragonal phases as 26 meV and 19 meV, respectively. Nevertheless, power-conversion efficiencies η up to 13% (11.5% stabilized) demonstrate good charge-carrier separation in the devices due to sufficient thermal dissociation and Sommerfeld-enhanced absorption.

中文翻译：

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钙钛矿太阳能电池电吸收光谱中光学跃迁的激子性质

我们使用温度相关电吸收 (EA) 光谱研究溶液处理钙钛矿太阳能电池的电子结构。同时测量半透明甲基铵碘化铅太阳能电池的吸收光谱和电调制光谱有助于直接比较特定特征。利用基于 Kramers-Kronig 关系的方法，可以将 EA 光谱转换为峰状线形。得到的峰位置与从广义 Elliott 拟合导出的吸收光谱的离散激子贡献（而不是连续谱）很好地对应。这表明观察到的 EA 共振的激子性质，并且发现在整个研究温度范围内（从 T = 10 K 到室温）是一致的。为了进一步证实这些发现，对测量的 EA 光谱进行线形分析。最好的一致性是使用类似一阶导数的函数形式实现的，该函数形式预期用于激子系统并支持激子光学跃迁的结论。正交相和四方相的激子结合能 EB 分别估计为 26 meV 和 19 meV。尽管如此，由于充分的热解离和索末菲增强的吸收，高达 13%（稳定 11.5%）的功率转换效率在器件中表现出良好的电荷载流子分离。正交相和四方相的激子结合能 EB 分别估计为 26 meV 和 19 meV。尽管如此，由于充分的热解离和索末菲增强的吸收，高达 13%（稳定 11.5%）的功率转换效率在器件中表现出良好的电荷载流子分离。正交相和四方相的激子结合能 EB 分别估计为 26 meV 和 19 meV。尽管如此，由于充分的热解离和索末菲增强的吸收，高达 13%（稳定 11.5%）的功率转换效率在器件中表现出良好的电荷载流子分离。