N‐Type Surface Doping of MAPbI₃ via Charge Transfer from Small Molecules

Abstract

Organic hole and electron transport materials are regularly employed as electron‐ and hole‐blocking layers in perovskite thin‐film solar cells. In order to optimize charge extraction in the device, these organic layers can be doped using organic small molecules. However, to date there is little work carried out on direct doping of perovskite surfaces. In this report, the change in electrical properties of thin films of MAPbI3 by surface doping the film with an organic dopant molecule: cobaltocene (Co(C5H5)2) is studied. By varying the quantity of cobaltocene deposited, the conductivity of MAPbI3 thin films is observed to be tunable over several orders of magnitude. A tunable shift in the Fermi level illustrating that charge transfer doping enables control over the interfacial energy levels, is observed. An increase in photoconductivity is seen at intermediate doping levels, indicating passivation of surface traps confirmed by increased photoluminescence. This model system provides a means to understand more complex heterointerfaces of doped organic blends at perovskite surfaces.

p-Type molecular doping by charge transfer in halide perovskite

“…11,12 Molecular doping appears among the most promising techniques for perovskites, with early works suggesting efficient tuning of the carrier properties at the film surface through charge transfer with a sequentially-deposited molecular layer. 13,14 Yet, more homogeneous perovskite doping with molecular dopants is still in its infancy, showing only modest conductivity improvements. [15][16][17][18] Doping of a particular perovskite host through charge transfer requires appropriate selection of the molecular dopant.…”

High‐Performance Planar Heterojunction Perovskite Solar Cells Based on BaCl2 Additive and Power Conversion Efficiency of Over 21%

“…[12][13][14][15][16] Improving the performance of planar PSCs is critically dependent on the properties of both their perovskite active layers and interfaces. [17][18][19] Therefore, controlling over their interface properties to obtain efficient transport and to minimize trapping of charge carriers is essential. For instance, buffer layer is inserted to reduce the lattice mismatch induced interface stress and induce more ordered crystal growth.…”

A new family of liquid and solid guanidine-based n-type dopants for solution-processed perovskite solar cells

“…We previously found that increase the doping of ETLs can lead to decomposition of the surface of MAPbI 3 by inducing release of iodine. 42 It is possible that similar degradation happens here in the highly doped devices, increasing the resistance at the MAPbI 3 /PC 61 BM interface and blocking charge extraction from the bulk of the active layer.…”