Optimized Phase Separation and Reduced Geminate Recombination in High Fill Factor Small-Molecule Organic Solar Cells

Abstract

In recent years, a rapid increase in the power conversion efficiency above 10% in small-molecule-based organic solar cells (SM-OSCs) has been made possible. However, one of the key device parameters, fill factor (FF), which is mainly limited by comprehensive courses, including charge generation, recombination, transport, and extraction, still remains moderate. Here we demonstrate a record high FF of 78.35% in SM-OSCs obtained through dichloromethane solvent vapor annealing, which provides optimized phaseseparation morphology for efficient charge generation and facilitates charge transport and extraction at the same time. We use a combined charge dynamic measurement and current−voltage characteristic reconstruction to identify that geminate recombination loss that resulted from undesired film morphology is mainly responsible for low FF in the pristine devices. Even higher FF that is comparable with that of crystal silicon solar cells in organic solar cells is very likely with the presence of charge mobility around 5 × 10 −3 cm 2 V −1 s −1 and proper film morphology.

Hole‐Transfer Dependence on Blend Morphology and Energy Level Alignment in Polymer: ITIC Photovoltaic Materials

“…The advent of new NFAs based on IDTs such as 2,2′‐[[6,6,12,12‐tetrakis(4‐hexylphenyl)‐6,12‐dihydro‐dithieno[2,3‐ d :2′,3′‐ d ′]‐s‐indaceno[1,2‐ b :5,6‐ b ′]dithiophene‐2,8‐diyl]bis[methylidyne(3‐oxo‐1 H ‐indene‐2,1(3 H )‐diylidene)]]bis[propanedinitrile] ( ITIC ; Figure a), has afforded OPV PCEs rivaling or exceeding those of the best fullerene materials . Nevertheless, the best performing NFA‐based BHJ blends exhibit lower FFs than typically observed with fullerenes . This laboratory previously reported polymeric BHJ OPVs displaying exceptional FFs when paired with fullerene acceptors.…”

Developing High‐Performance Electron‐Rich Unit End‐Capped Wide Bandgap Oligomeric Donor by Weak Electron‐Deficient Central Core Strategy

“…The measured the electron mobility ( µ e ) in each blend film was also included in Table for comparison, which showed a slight increase upon SVA treatment and TA+SVA treatment. Nevertheless, besides higher charge mobility, the BTA6F/PC 71 BM devices upon either SVA treatment or TA+SVA treatment also possess more balanced hole and electron mobility, which is one of the most important prerequisite to achieve high FF over 0.7 in the devices …”

Nonfullerene organic photovoltaic cells exhibiting 13.76% efficiency by employing upside‐down solvent vapor annealing

“…Figure 1A shows the molecular structures of PM7 and IT-4Cl. [38][39][40][41][42] Among the different annealing solvents, CS 2 is the best solvent to finely regulate and control morphology of active layers. The OPVs with a normal structure of ITO/PEDOT:PSS/PM7:IT-4Cl/PDIN/Al ( Figure 1C) were fabricated with different UD-SVA treatment.…”

“…The decreased V OC of the OPVs with different UD-SVA treatment should be ascribed to the increased intermolecular interaction of used materials as well as faster charge transport and collection; the related discussions on this phenomenon have been commonly reported in some works. [38][39][40][41][42] Among the different annealing solvents, CS 2 is the best solvent to finely regulate and control morphology of active layers. The OPVs with CS 2 UD-SVA treatment display a PCE of 13.76% along with a J SC of 20.53 mA cm −2 , a FF of 77.05%, and a V OC of 0.870 V. More than 15% PCE improvement can be achieved for OPVs with CS 2 as annealing solvent compared with the as-cast OPVs.…”