Promotion Strategies of Hole Transport Materials by Electronic and Steric Controls for n–i–p Perovskite Solar Cells

Abstract

Hole transport materials (HTMs) play a requisite role in n-i-p perovskite solar cells (PSCs). The properties of HTMs, such as hole extraction efficiency, chemical compatibility, film morphology, ion migration barrier, and so on, significantly affect PSCs' power conversion efficiencies (PCEs) and stabilities. Up till now, researchers have devoted much attention to developing new types of HTMs as well as promoting pristine HTMs using numerous strategies. In this Review, we summarize the design strategies of various common HTMs for n-i-p PSCs are comprehensively discussed from two separate aspects (additive and non-additive engineering). Additive engineering generally tunes electronic properties of HTMs while non-additive engineering basically modifies their steric structures. Critical analysis and comparison between these design strategies are provided, considering the overall PCEs and stabilities of PSCs. Finally, a brief perspective on future promising design strategies for HTMs is given, in order to fabricate efficient and stable n-i-p devices for the commercialization of PSCs.

Novel Push-Pull Benzodithiophene-Containing Polymers as Hole-Transport Materials for Efficient Perovskite Solar Cells

“…In sum, the development of dopant-free, cost-effective HTMs with tunable electronic properties—high hole mobilities is of great importance. Moreover, good film formation properties of HTMs and uniform morphology of films are substantial aspects for the fabrication of high-performance PSCs [ 9 , 10 ]. In this regard, benzo[1,2-b:4,5-b′]dithiophene-based (BDT) conjugated polymers can be considered as prospective HTMs.…”

A N‐Ethylcarbazole‐Terminated Spiro‐Type Hole‐Transporting Material for Efficient and Stable Perovskite Solar Cells

“…[3][4][5][6][7][8][9][10] In general, in addition to achieving high device efficiency, extracting holes from perovskite layers, and inhibiting non-radiative recombination, hole-transporting materials (HTMs) have been reported in numerous articles to improve the stability of PSCs. [11][12][13][14][15][16] Nowadays, different types of organic HTMs have been applied in efficient PSCs, including linear, star-shaped, or spirocentered structures. [17][18][19][20][21] Among them, spiro-centered molecules, especially 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD), are still recognized as the most efficient HTM in PSCs [22] because of the superiority from their twisted structures granting suitable energy levels for transporting holes and blocking electrons.…”

Broadly Applicable Synthesis of Heteroarylated Dithieno[3,2-b:2′,3′-d]pyrroles for Advanced Organic Materials – Part 2: Hole-Transporting Materials for Perovskite Solar Cells

“…15,16 A major disadvantage of spiro-OMeTAD is the low glass transition temperature decreasing the thermal stability. 17 Many new organic HTMs have been developed in recent years [18][19][20][21] but the highest efficient PSCs still rely on spiro-OMeTAD.…”