Intensive Exposure of Functional Rings of a Polymeric Hole‐Transporting Material Enables Efficient Perovskite Solar Cells

Abstract

A variety of dopant-free hole-transporting materials (HTMs) is effectively applied in perovskite solar cells (PSCs); however, HTMs with the additional function of HTM/perovskite interfacial optimization that is crucial to their photovoltaic performance are really limited. In this work, the design of an HTM bearing an intensive exposure of its functional aromatic rings to perovskite layer via side-chain engineering is attempted. With an edge-on orientation and a short distance to perovskite, this HTM was expected to display an excellent ability to extract holes from and passivate defects in the perovskite layer. To demonstrate this strategy, an alternating copolymer was constructed with a 2,5-di-2-ethylhexyloxy-1,4-phenylene unit and a bithiophene unit, and the PSC based on this polymer showed an ultrahigh short-circuit current density of 25.50 mA cm , which was the highest so far presented by dopant-free organic HTMs. A comparable power conversion efficiency of 19.68% (certified: 19.5%) to that of a control 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) device (19.81%) was thus obtained, which is the highest value ever reported for mesoporous PSCs based on dopant-free polymeric HTMs.

Hydrothermally Treated SnO2 as the Electron Transport Layer in High‐Efficiency Flexible Perovskite Solar Cells with a Certificated Efficiency of 17.3%

“…As shown in Figure d, the trap densities of state (tDOS) for the PSCs with different ETLs were calculated from the TAS analysis. As reported in previous literature, the region with energies lower than 0.30 eV is denoted as the shallow trap state and that with energies above 0.30 eV is denoted as the deep trap state, corresponding to the defect concentrations in the bulk of the perovskite layer and on the surface of the perovskite layer, respectively . The PSCs based on AD‐SnO 2 exhibit the highest concentration of shallow trap states among the AD‐SnO 2‐ , TA‐SnO 2‐ and HT‐SnO 2 ‐based PSCs, which indicates that more defects are present in the bulk of the perovskite film, resulting from the presence of pinholes as shown in Figure d.…”

“…Although organic transport materials, such as phenyl‐C61‐butyric acid methyl ester (PCBM), poly(3‐hexylthiophene) (P3HT), and poly(bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine) (PTAA), can be processed at low temperatures and directly used in flexible PSCs, their high costs and low stabilities hinder the large‐scale production of flexible PSCs . Utilizing inorganic ETLs should be a much more effective strategy because they have greater stability than organic ETLs; however, most inorganic ETLs have to be processed at high temperatures or vacuum, which limits their utilization in flexible PSCs …”

Development of Dopant‐Free Organic Hole Transporting Materials for Perovskite Solar Cells

“…This HTM based on triazatruxene, thiophene, and malononitrile moieties was fabricated in (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 devices, which rendered a PCE of 19% without any dopants. Apart from small molecules, Zhang et al designed a simple structured copolymer, 2,5‐dialkoxyl‐1,4‐phenylene unit and bithiophene unit, (DTB) with 2,5‐dialkoxyl‐1,4‐phenylene unit and bithiophene unit . The PCE using undoped DTB led to a superior passivation effect to the defects on the surface of the perovskite, resulting in a higher extraction efficiency of 19.5% compared with the typical Spiro‐OMeTAD (19.81%) under identical conditions.…”

Hole Transport Materials in Conventional Structural (n–i–p) Perovskite Solar Cells: From Past to the Future

“…c) Molecular orientation of DTB and J – V curve of its device. Reproduced with permission . Copyright 2018, Wiley.…”

“…Therefore, PCDTBT1 , which has short alkoxy side‐chains, exhibited the highest efficiency in the Per‐SC and a high stability (90% over 30 days) in the ambient condition (40–70% RH and 25–35 °C). Xu and co‐workers reported the copolymer ( DTB ) composed of dithiophene and benzene, which exhibited 19.68% of efficiency (Figure c) . Interestingly, the DTB has an edge‐on orientation generally believed not to be appropriate for solar cell structures because of the lateral π–π stacking opposite to the favorable direction for solar cells; thus, it has a relatively low hole mobility (SCLC, 1.0 × 10 −4 cm 2 V −1 s −1 ).…”