Unraveling the efficiency-limiting morphological issues of the perylene diimide-based non-fullerene organic solar cells

Abstract

Herein we report a comparative morphological analysis of the perylene diimide (PDI)- and fullerene-based organic solar cells (OSCs) to identify the factors responsible for low performance of PDI-based devices. A PDI derivative, bis-PDI, and a fullerene derivative, PC70BM, are mixed with an efficient polymer donor, PffBT4T-2OD. The large disparity in power conversion efficiencies (PCEs) of OSCs composed of PffBT4T-2OD:bis-PDI (PCE = 5.18%) and PffBT4T-2OD:PC70BM (PCE = 10.19%) observed are attributed to differences in the nanostructural motif of bulk heterojunction (BHJ) morphologies of these blend systems. The X-ray scattering and surface energy characterizations revealed that the structurally dissimilar bis-PDI and PC70BM molecules determine the variation in blend film morphologies, and in particular, the molecular packing features of the donor PffBT4T-2OD polymer. In addition, high-resolution transmission electron microscopy (HRTEM) images explore the BHJ morphologies and presence of longer polymer fibrils in PffBT4T-2OD:bis-PDI system, justifying the unbalanced charge transport and high hole mobility. The low performance of PffBT4T-2OD:bis-PDI devices was further investigated by studying charge carrier recombination dynamics by using light-intensity-dependent and transient photovoltage (TPV) experiments. Furthermore, the temperature-dependent experiments showed the photovoltaic properties, including charge recombination losses, are strongly affected by energetic disorder present in bis-PDI-based system.

Cationic Imidazolium Polythiophenes: Effects of Imidazolium-Methylation on Solution Concentration-Driven Aggregation and Surface Free Energy of Films Processed from Solvents with Different Polarity

“…For example, a difference of around 10 mN/m in γ S between layers (29.1 and 41.1 mN/m) promotes poor miscibility, producing a slightly larger phase-separated film morphology. 22 , 25 , 26 However, when this difference decreases to around 2.5 mN/m (29.1 and 31.6 mN/m), penetration and diffusion of the fullerene into the polymer region are promoted. 11 , 22 , 25 , 26 …”

Ternary Blend Strategy for Achieving High‐Efficiency Organic Photovoltaic Devices for Indoor Applications

“…In our work, we noticed that under 500 lx light conditions, the FF increased significantly, up to around 68.5 %, and the V OC increased by approximately 0.05 V in the device prepared with the same weight percentage of EP‐PDI (40 wt %). The increase in FF was assigned to the better charge transport and charge extraction properties of the system (described in the next section), and the increase in V OC can be attributed to the increase in R Sh or the higher LUMO level of the EP‐PDI in blend system …”

“…The ITO‐coated glass substrates were cleaned as reported earlier . After UV/ozone treatment for 30 min, a ZnO solution, prepared as reported in previous work, was spin coated at 4000 rpm on each substrate and then the resulting composite was baked at 150 °C for 30 min on a hot plate. The reference binary solution, consisting specifically of PTB7 and PC 71 BM, was prepared with a PTB7/PC 71 BM ratio of 1:1.5 (wt %), with a concentration of the donor polymer PTB7 of approximately 12 mg mL −1 , in chlorobenzene (CB)/1,8‐diiodooctane (DIO, 97:3 vol %) solvent.…”

Indeno[1,2-b]thiophene End-capped Perylene Diimide: Should the 1,6-Regioisomers be systematically considered as a byproduct?

“…Although these records were reached with indacenodithiophene derivatives, perylene diimides (PDIs) have always held an important place among the electron transporting materials due to their excellent thermal, chemical and photochemical stabilities combined with their singular optical, redox and charge transport properties 9,10 . Nonetheless, the PDI extended π-conjugated structure typically suffers from an excessive π-π stacking tendency, forming micrometer-sized crystallites that are detrimental for an efficient charge separation in bulk heterojunction (BHJ) solar cells [11][12][13][14] . To tackle this problem, important efforts have been devoted to functionalize the peripheral positions, namely the bay (1,6,7,12) and ortho positions (2,5,8,11) 3,9,[15][16][17][18] , leading to profuse design principles and above all, to a better understanding of the structure-property relationships (Fig.…”

“…Nonetheless, the PDI extended π-conjugated structure typically suffers from an excessive π-π stacking tendency, forming micrometer-sized crystallites that are detrimental for an efficient charge separation in bulk heterojunction (BHJ) solar cells [11][12][13][14] . To tackle this problem, important efforts have been devoted to functionalize the peripheral positions, namely the bay (1,6,7,12) and ortho positions (2,5,8,11) 3,9,[15][16][17][18] , leading to profuse design principles and above all, to a better understanding of the structure-property relationships (Fig. 1) [19][20][21][22][23][24][25][26][27][28] .…”