Spiro‐Linked Molecular Hole‐Transport Materials for Highly Efficient Inverted Perovskite Solar Cells

Abstract

Spiro‐linked compounds have been used as benchmark hole‐transport materials (HTMs) for the construction of efficient normal architecture (n‐i‐p) perovskite solar cells (PSCs). However, the heavy reliance on the use of dopants not only complicates the device fabrication but imposes long‐term stability concern of the devices. Herein, it is reported that solution‐processed dopant‐free spiro molecules can serve as superior HTMs to fabricate efficient inverted (p‐i‐n) PSCs. Rational choice of orthogonal solvent allows us to solution deposit uniform and pinhole‐free perovskite films without compromising the hole‐extraction capability of the spiro‐based interface layers. To illustrate the generality of the strategy, three spiro‐linked molecules are investigated side by side as HTMs in one‐step solution‐processed CH3NH3PbI3 PSCs. Due to the favored energy‐level alignment and high hole mobility, solar cells based on the HTM of spiro‐TTB yield a high efficiency of 18.38% with open‐circuit voltages (VOC) up to 1.09 V. These results suggest that small molecular HTMs commonly developed for normal structure devices can be of great potential to fabricate cost‐effective and highly efficient inverted PSCs.

Examining the Interfacial Defect Passivation with Chlorinated Organic Salt for Highly Efficient and Stable Perovskite Solar Cells

“…Currently, there are lots of approaches to improve the performance and stability of PSCs, containing additive engineering, using additive into a perovskite absorber layer and interface engineering, modifying the hole transport layer (HTL)/perovskite or perovskite/electron transport layer (ETL) interfaces. [ 23–26 ] The treatment of perovskite film by various modifying agents has been proved to be an effective strategy to passivate the interface defects and remarkably enhance the surface quality and ambient environment stability of the perovskite layer. For example, nonstoichiometric ratio of PbI 2 in the perovskite film presented at the grain boundaries or on the surface can decrease charge recombination by the creation of I‐type band alignment.…”

Enamine‐Based Cross‐Linkable Hole‐Transporting Materials for Perovskite Solar Cells

“…[ 19 ] Recently, different small‐molecule HTMs for p–i–n have been reported, such as MPA‐BTTI, [ 20 ] BTF4, [ 21 ] and BDPSO; [ 22 ] however, their number is still rather limited due to the aforementioned restriction. Therefore, as an alternative, several strategies have been reported, e.g., change of the perovskite precursor solvent, [ 23 ] use of self‐assembled monolayers, [ 24 ] and use of soluble precursors that are subsequently transformed into insoluble films. [ 25 ] In addition, recently cross‐linkable HTMs were introduced into inverted devices, resulting in relatively high performance.…”

A Review on Solution‐Processable Dopant‐Free Small Molecules as Hole‐Transporting Materials for Efficient Perovskite Solar Cells

“…[75][76][77][78] Mai et al adopted the same core unit as that of spiro-OMeTAD through replacing the outside methoxyl groups with methyl or hydrogen groups, and named them as Spiro-TTB and Spiro-TAD, respectively. [78] The target SM-HTMs showed two to ten times increased hole mobility higher than that of spiro-OMeTAD, and this increase could fully satisfy the requirement for HTMs used in inverted PSCs, since a thickness of only a few tens of nanometers could already be adequate for these HTLs. The authors selected a mixed solvent of gamma-butyrolactone and dimethyl sulfoxide to dissolve the perovskite precursors, in order to prevent the damage to the beneath HTL.…”

“…Finally, through a delicate designing of the core units and a careful choice of the peripheral arms, much enhanced performance in the respect of both PCE and long-term stability could be expected according the principles we raised in this review. 15.9 [75] 1 0 MAPbI 3 18.41 [78] Tricyclic Carbazole 0 0 MAPbI 3−x Cl x 17.60 [87] 17.8 [89] Fluorene 15.23 [91] 4 2 (MAPbI 3 ) 0.9 (FAPbICl 2 ) 0.1 20.60 [92] Thiophene fused 21.04 [101] 1 1 MAPbI 3-x Cl x 21.12 [102] Simple rings Single ring 1 0 MAPbI 3 18.03 [111] 3 1 FA 0.9 Cs 0.1 PbI 3 21.0 [119] Bicyclic ----1 0 CsMAFA 18.78 [120] Polycyclic [130] Hexacyclic 0 0 MAPbI 3 17.5 [133] ----Heptacyclic 0 0 MAPbI 3 15.7 [136] 1 0 MAPbI 3 18.6 [134] w/o TPA/ DPA 19.67 [139] Donor + Acceptor Symmetric ----3 2 FA 0.85 MA 0.15 PbI 3 20.56 [146] Asymmetric ----1 0 MAPbI 3 18.75 [152] Donor only 2 0 MAPbI 3 18.2 [157] 1 1 MAPbI 3 19.16 [156] Figure 15. Designing principles for high-performance dopant-free SM-HTMs.…”