Positional Effect of the Triphenylamine Group on the Optical and Charge‐Transfer Properties of Thiophene‐Based Hole‐Transporting Materials

Abstract

Hybrid organic-inorganic perovskite solar cells (PSCs) have shown significant potentialf or use in the energy field. Typically,h ole-transporting materials (HTMs) play an important role in affectingt he power conversion efficiency (PCE) of PSCs. Adeep understandingofthe structure-property relationship plays avital role in developing efficient HTMs. Herein, the relationship betweent he structure and properties of two small organic HTMs H2,5 and H3,4 weres ystematically investigated in terms of the electronic and optical properties, the hole-transporting behavior by using density functional theory (DFT)a nd Marcus electron transfer theory. The resultsdemonstrated that the high power conversion efficiency of the H2,5-based PSCw as causedb ys trong interactions with the perovskite material on the interface and an enhanced hole mobility in H2,5 compared with H3,4.T he strong interaction derives from the short bond length of O atom of HTM and Pb atom of perovskite material, andt he highly hole mobility derives from the quasi-planar conjugated conformation and tight packingm odel of neighboring molecules in H2,5.I na ddition, we found that the planar structure enhances the intermolecular interaction between HTM and perovskite materials compared with the 'V'-shaped molecule. Importantly,w ea lso notet hat the HOMO level of the isolated molecule is not always proportional to the open-circuit voltages of PSCs since the HOMO level might move towardahigher level when the interaction between HTM and interface of perovskite was included. The work gives essential information for rational designing efficient HTMs.[a] Dr. Results and DiscussionElectronicstructures of H2,5 and H3,4Recently,D ai et al. developed two new HTMs based on thiophene and triphenylamine, called H2,5 and H3,4 in their work. [11] The substitution positione ffect of H2,5 and H3,4 on the performance of PSCs was studied. Their resultss howed that PSC based on H2,5 exhibits aP CE of 15.13 %, while PCE is only 9.05 %b ased on H3,4.H erein, to explain the noteworthy different in PEC, we investigated geometries and electronic structure properties of H2,5 and H3,4.T wo molecular struc-Scheme1.Calculation procedureofh ole mobility.

Rational design of small molecule hole-transporting materials with a linear π-bridge for highly efficient perovskite solar cells

“…7, the optimized dimeric structures of all molecules exhibit a predominant face-to-face packing, which is favorable to raising the effective p-orbital overlap and enhancing the hole transport ability. 94 As displayed in Table 2, the hole mobility calculated for Spiro-OMeTAD is 3.14 Â 10 À3 cm 2 V À1 s À1 , which is in good agreement with the reported experimental and theoretical values. 95,96 Theoretically, an efficient HTM should have hole mobility in the range of 10 À3 -10 À4 cm 2 V À1 s À1 .…”

Isomeric D‐π‐D Dopant‐Free Hole Transport Materials: Effect of the Substitution Position and Heteroatom on the Performance of Perovskite Solar Cells

“…Moreover, the heteroatom does not show any regular effect on the HOMO energy level. Generally, the molecules with better conjugation ability would exhibit higher HOMO levels, [28,40,44] and the molecules with S exhibit lower HOMO levels compared with the O counterparts in this work [25,26] . As the valence band of the perovskite herein is about −5.65 eV, suggesting that the molecules feature favorable driving force for hole extraction [45,46] .…”

“…Moreover, the heteroatom does not show any regular effect on the HOMO energy level. Generally, the molecules with better conjugation ability would exhibit higher HOMO levels, [28,40,44] and the molecules with S exhibit lower HOMO levels compared with…”

A π-extended triphenylamine based dopant-free hole-transporting material for perovskite solar cells via heteroatom substitution

“…The hole transport behaviour at the interfaces between HTMs and perovskite layers can directly affect the PCEs of PSCs. [52][53][54] In general, a fast hole transport at the interface could increase the short-circuit current density of PSCs. We focus on the CH 3 NH 3 PbI 3 (001) face because it is one of the most stable surfaces and is found to be favorable for the hole transport.…”