Inhibited Aggregation of Lithium Salt in Spiro-OMeTAD for Perovskite Solar Cells

• Organic small molecule material, spiro-OMeTAD , is widely used in Perovskite solar cells  as the hole transport material due to its desirable properties, such as suitable highest occupied molecular orbital energy levels, high solubility and good film forming ability. However, the aggregation and hydrolysis of the common additive, Li-TFSI, in the spiro-OMeTAD, lead to the existence of voids/pinholes in the hole transport layer, which limits further improvement of perovskite solar cell efficiency. Here, we develop a low-cost and easy-fabrication technique to substantially reduce the undesired voids in hole transport layer by modifying it with commercially available PbI2 .

  
  

  The strong interaction between the PbI2 and the TBP retards the evaporation of TBP, which hinders the agglomeration of Li-TFSI and generation of voids in the HTL. Consequently, the HTL shows a dramatically improved mobility and efficiency of charge carrier extraction, leading to a better response to steady-state condition with less than 1s for the corresponding photovoltaic device (where the control device shows more than 26s). A champion power conversion efficiency of over 20% is obtained from PbI2 added devices by optimizing its adding amount. This work provides a facile and effective strategy to improve the performance of the hole transport materials and perovskite solar cells. 

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• Graphical abstract

  Adding PbI2 in spiro-OMeTAD precursor solution inhibits the aggregation of Li-TFSI, which improves the mobility and charge carrier extraction in HTLs. PbI2 , Aggregation of Li-TFSIPassivation, Hole transport layer Perovskite solar cells

• Graphical abstract

  Adding PbI2 in spiro-OMeTAD precursor solution inhibits the aggregation of Li-TFSI, which improves the mobility and charge carrier extraction in HTLs. PbI2 , Aggregation of Li-TFSIPassivation, Hole transport layer Perovskite solar cells

• Highlights

  • PbI2 significantly inhibits the aggregation of Li-TFSI in spiro-OMeTAD.

  • Adding PbI2 in spiro-OMeTAD generates a dense and uniform HTL film without voids.

  • Fast charge extraction of the PbI2-added spiro-OMeTAD is verified.

  • PCE of the devices is improved from 17.6% to 20.3% by adding PbI2 in spiro-OMeTAD.