溶剂工程调控钙钛矿薄膜中PbI2和PbI2(DMSO)的形成

钙钛矿太阳能电池以其高效、低成本的特点备受关注。到目前为止，钙钛矿太阳能电池的最高光电转换效率已经超过25%，显示出良好的应用前景。钙钛矿薄膜的结晶性能是决定器件性能的关键，因此，调控钙钛矿薄膜的生长过程至关重要。本工作中，我们发现通过简单调节前驱体溶剂，即调节二甲基亚砜：1, 4-丁内酯: N, N-二甲基甲酰胺(DMSO : GBL : DMF)的三种混合溶剂的比例，可实现钙钛矿薄膜中PbI₂和PbI₂(DMSO)含量的调节，从而调节电池的器件性能。此外，本工作系统研究了PbI₂和PbI₂(DMSO)的含量对器件性能的影响。结果表明，PbI₂(DMSO)的形成会导致300–425 nm波长范围内电池的外量子效率(EQE)降低，从而导致器件性能下降。相反，通过在前驱体溶液中添加额外的碘化亚甲基铵(MAI)，可以抑制PbI₂和PbI₂(DMSO)的形成。

Controllable Formation of PbI2 and PbI2(DMSO) Nano Domains in Perovskite Films through Precursor Solvent Engineering

Perovskite solar cells (PSCs) attract much attention for their high efficiency and low processing cost. Power conversion efficiencies (PCEs) higher than 25% have been reported in literature, demonstrating the excellent application prospect of PSCs. In general, the crystallinity and the film composition of perovskite thin films are significant factors in determining device performance. Much effort has been made to control the growth process of perovskite films through the use of additives, passivation layers, special atmosphere treatments, precursor regulation etc. Among these methods, precursor solvent engineering is a simple and direct way to control the perovskite quality, but the controllability of components through solvent engineering is still difficult and has not yet been reported. Herein, we report the controlled formation of PbI₂ and PbI₂ with dimethyl sulfoxide (DMSO) nano domains through precursor solvent engineering. In particular, tuning the solvent content of the dimethyl sulfoxide: 1, 4-butyrolactone: N, N-dimethylformamide (DMSO : GBL : DMF) in the perovskite precursor solution, controlled the content of PbI₂ and PbI₂(DMSO) domains. Due to the lower boiling point and weaker coordination of DMF relative to DMSO, part of methylammonium iodide (MAI) would escape from the wet films during the evaporation process. Therefore, the PbI₂(DMSO) can't completely convert to perovskite crystals and is retained in the final films as residual PbI₂(DMSO) domains. Both UV-vis absorption spectrum and XRD spectrum confirmed the existence of PbI₂ and PbI₂(DMSO) domains. Importantly, the content of PbI₂(DMSO) was controllable by simply changing the relative proportion of DMF. With an increase in the DMF content, the residual PbI₂(DMSO) domains gradually increase. In addition, the influence of PbI₂ and PbI₂(DMSO) domains on the device performance was systematically investigated. The formation of PbI₂(DMSO) domains caused a decrease in external quantum efficiency (EQE) of the device over 300–425 nm, and consequently decreased the device performance. That was because the PbI₂(DMSO) domain has strong absorption over 300–425 nm. Therefore, the PbI₂(DMSO) domains would absorb the photons over 300–425 nm prior to the perovskite, however the photons absorbed by the PbI₂(DMSO) domains are not converted into the photocurrent. Thus, the perovskite solar cell containing PbI₂(DMSO) showed an EQE loss over 300–425 nm in the EQE spectra. This work provides a simple method to control the components, especially the content of the PbI₂(DMSO) domains, in perovskite films through regulating the precursor solvent. Additionally, this work revealed a PbI₂(DMSO) domain related EQE loss phenomenon, highlighting the importance of controlling this component.