A New Wide Bandgap Donor Polymer for Efficient Nonfullerene Organic Solar Cells with a Large Open‐Circuit Voltage

Abstract

Significant progress has been made in nonfullerene small molecule acceptors (NF‐SMAs) that leads to a consistent increase of power conversion efficiency (PCE) of nonfullerene organic solar cells (NF‐OSCs). To achieve better compatibility with high‐performance NF‐SMAs, the direction of molecular design for donor polymers is toward wide bandgap (WBG), tailored properties, and preferentially ecofriendly processability for device fabrication. Here, a weak acceptor unit, methyl 2,5‐dibromo‐4‐fluorothiophene‐3‐carboxylate (FE‐T), is synthesized and copolymerized with benzo[1,2‐b:4,5‐b′]dithiophene (BDT) to afford a series of nonhalogenated solvent processable WBG polymers P1‐P3 with a distinct side chain on FE‐T. The incorporation of FE‐T leads to polymers with a deep highest occupied molecular orbital (HOMO) level of −5.60−5.70 eV, a complementary absorption to NF‐SMAs, and a planar molecular conformation. When combined with the narrow bandgap acceptor ITIC‐Th, the solar cell based on P1 with the shortest methyl chain on FE‐T achieves a PCE of 11.39% with a large V oc of 1.01 V and a J sc of 17.89 mA cm−2. Moreover, a PCE of 12.11% is attained for ternary cells based on WBG P1, narrow bandgap PTB7‐Th, and acceptor IEICO‐4F. These results demonstrate that the new FE‐T is a highly promising acceptor unit to construct WBG polymers for efficient NF‐OSCs.

Long-range exciton diffusion in non-fullerene acceptors and coarse bulk heterojunctions enable highly efficient organic photovoltaics

“…Previous studies of PTB7-Th blends with ITIC derivatives deposited by one-step spin-coating also showed ne granular morphology with roughly round grains. 35,36 Recent reports show that high efficiency can also be achieved in sequentially deposited donor acceptor layers which may have very different needle-like morphology. 37,38 Hence, assuming that acceptor domains have a spherical shape with a radius r, the ratio g(t) of the PL decay in a blend to the PL decay in a neat acceptor lm is described by…”

Improved Average Figure‐of‐Merit of High‐Efficiency Nonfullerene Solar Cells via Minor Combinatory Side Chain Approach

“…[36][37][38][39][40][41][42] To promote high PCEs, thiophene-based donor-acceptor type (D-A) polymers have been extensively investigated through fluorination, chlorination, esterification, and their combinations. [34,[43][44][45][46] However, most of the relevant high-performing polymers show estimated SC values of more than 36%, partly due to using of comonomers with relatively high SCs (Table S1 and S2, Supporting Information). For example, polymer PTO2 (namely, P15 in Chart S2, Supporting Information) can display a high single-junction efficiency of 14.7% but with a high SC value of 52.96% because of using a fluorinated electrondonating moiety with a high SC value of 60%.…”

Ternary Organic Solar Cell with a Near‐Infrared Absorbing Selenophene–Diketopyrrolopyrrole‐Based Nonfullerene Acceptor and an Efficiency above 10%

“…However, the applications of tandem organic solar cells (OSCs) are limited due to the difficulties in device fabrication and engineering . An interesting alternative to tandem OSCs are ternary solar cells, which combine the easy processing of binary OSCs with an improvement in the efficiency involving a trade‐off between open‐circuit voltage ( V oc ) and J sc . Such systems have given enhanced PCEs up to 12.2% together with improved photocurrent density, open‐circuit voltage, and fill factor (FF).…”