Impact of 9‐(4‐methoxyphenyl) Carbazole and Benzodithiophene Cores on Performance and Stability for Perovskite Solar Cells Based on Dopant‐Free Hole‐Transporting Materials

Abstract

Perovskite solar cells (PSCs) possess both high-power conversion efficiency (PCE) and good operation stability for future application. Although many different types of hole-transporting materials (HTMs) are assessed, few dopant-free small organic molecule HTMs-based PSC cells exist, which exhibit excellent stability under both heat and illumination. Herein, two novel HTMs that are based on 9-(4-methoxyphenyl) carbazole and benzodithiophene cores are synthesized and named N1,N1 0 -(9-(4-methoxyphenyl)-9H-carbazole-3,6-diyl)bis(N1-(4-(bis (4-methoxyphenyl)amino)phenyl)-N4,N4-bis(4-methoxyphenyl)benzene-1,4diamine) (PhCz-4MeOTPA) and N1,N1 0 -(benzo[1,2-b:4,5-b 0 ]dithiophene-2,6-diyl) bis(N1-(4-(bis(4-methoxyphenyl)amino)phenyl)-N4,N4-bis(4-methixyphenyl) benzene-1,4-diamine) (BDT-4MeOTPA). Of the two HTMs, PhCz-4MeOTPA possesses a lower level of planarity than that of BDT-4MeOTPA, which inhibits molecular stacking to improve film quality and increases hole-transport mobility and charge transport. A PCE of 16.04% is achieved with the application of dopantfree PhCz-4MeOTPA in PSCs, which is higher than that of dopant-free BDT-4MeOTPA. The unencapsulated PSC devices based on PhCz-4MeOTPA maintain 82% of their initial values under continuous sun illumination in an ambient environment at 40-45 C after 672 h and 92% of their initial values at 80 C in an ambient environment after 1200 h in the dark.With the intensification of the energy crisis, solar energy is being regarded as a potentially inexhaustible energy source. [1] Perovskite solar cells (PSCs) have received widespread attention over the past few years for their excellent characteristics, [2][3][4][5][6][7][8] such as high absorption coefficients, long diffusion lengths, broad spectral absorption ranges, and high charge carrier mobilities. [9][10][11] The power conversion efficiency (PCE) of PSCs has already increased from 3.8% [12] in 2009 to 23.7% [13] in 2018.In PSC cells, small organic holetransporting materials (HTMs) play a critical role in extracting holes from the perovskite layer, transporting these holes to the counter electrode, and preventing internal charge recombination, thereby improving the PSC efficiency. Among the different available HTMs, the triarylamine-based HTM 2,2 0 ,7,7 0 -tetrakis(N,N-di-p-methoxyphenylamine)-9,9 0 -spirobifluorene (Spiro-OMeTAD) is regarded as the most promising HTM because of its impressive efficiency. [14][15][16][17] Whereas a high PCE can only be achieved by doping additives, such as lithium bis(trifluoromethyl sulfonyl) imide (Li-TFSI) and 4-tert-butylpyridine (TBP), [18][19][20][21] this dopant compromises the stability of PSC cells. [22] Furthermore, Spiro-OMeTAD has some disadvantages, such as low stability under heat stress resulting from crystallization, a complex synthesis route, and cumbersome purification procedures, [14,23] all of which hinder its industrial application. Although numerous doped HTMs exhibit comparable efficiencies to that of Spiro-OMeTAD, [24][25][26][27][28][29][30][31][32][33] their sta...

Pyridine Bridging Diphenylamine-Carbazole with Linking Topology as Rational Hole Transporter for Perovskite Solar Cells Fabrication

“…In order to investigate the influence of linking topology on molecular structure, we calculate the representative dihedral angles between the pyridine core and DANCBZ arm. As shown (Figure3b), the 2,6PyDANCBZ with 56.76° and 35.95° dihedral angles owns a lower level of planarity as compared to 3,5PyDANCBZ with 46.61° and 38.58° dihedral angles, which reduces the molecular stacking and helps in the formation of uniform film in 2,6PyDANCBZ 50,51.…”

Additive Engineering for Efficient and Stable Perovskite Solar Cells

“…However, the high cost of synthesis of these materials along with the need to use hydrophilic dopants present a challenge to PSC development. The stability issue under heat stress at 85 °C could limit practical applications . Attempts have been made to develop more cost‐effective and dopant‐free HTMs or some other efficient dopants for potential commercial applications of PSCs .…”

Recent Progress in Perovskite Solar Cells Modified by Sulfur Compounds

“…To fabricate an efficient and stable device, dopant‐free BDT‐based HTMs have been developed. [ 150 ] Chen et al used BDT as the core, thiophene, and benzo‐[c][1,2,5]‐thiadiazole (BTZ) derivatives as π ‐conjugation components and obtained a novel dopant‐free HTM BDT‐C1. [ 151 ] BDT‐C1 demonstrated a favorable HOMO level at −5.26 eV, as well as remarkable hole mobility and conductivity even without a dopant.…”