Single-Junction Organic Solar Cell with over 15% Efficiency Using Fused-Ring Acceptor with Electron-Deficient Core

A new polymer donor (PBDB-T-SF) and a new small molecule acceptor (IT-4F) for fullerene-free organic solar cells (OSCs) were designed and synthesized The influences of fluorination on the absorption spectra, molecular energy levels, and charge mobilities of the donor and acceptor were systematically studied The PBDB-T-SF:IT-4F-based OSC device showed a record high efficiency of 131%, and an efficiency of over 12% can be obtained with a thickness of 100–200 nm, suggesting the promise of fullerene-free OSCs in practical applications

Molecular Optimization Enables over 13% Efficiency in Organic Solar Cells

18% Efficiency organic solar cells

Organic solar cells (OSCs) have been dominated by donor:acceptor blends based on fullerene acceptors for over two decades. This situation has changed recently, with non-fullerene (NF) OSCs developing very quickly. The power conversion efficiencies of NF OSCs have now reached a value of over 13%, which is higher than the best fullerene-based OSCs. NF acceptors show great tunability in absorption spectra and electron energy levels, providing a wide range of new opportunities. The coexistence of low voltage losses and high current generation indicates that new regimes of device physics and photophysics are reached in these systems. This Review highlights these opportunities made possible by NF acceptors, and also discuss the challenges facing the development of NF OSCs for practical applications.

/pdf/organic-solar-cells-based-on-non-fullerene-acceptors-2xrgk24kh9.pdf

Organic solar cells based on non-fullerene acceptors.

Non-fullerene acceptors (NFAs) are currently a major focus of research in the development of bulk-heterojunction organic solar cells (OSCs). In contrast to the widely used fullerene acceptors (FAs), the optical properties and electronic energy levels of NFAs can be readily tuned. NFA-based OSCs can also achieve greater thermal stability and photochemical stability, as well as longer device lifetimes, than their FA-based counterparts. Historically, the performance of NFA OSCs has lagged behind that of fullerene devices. However, recent developments have led to a rapid increase in power conversion efficiencies for NFA OSCs, with values now exceeding 13%, demonstrating the viability of using NFAs to replace FAs in next-generation high-performance OSCs. This Review discusses the important work that has led to this remarkable progress, focusing on the two most promising NFA classes to date: rylene diimide-based materials and materials based on fused aromatic cores with strong electron-accepting end groups. The key structure–property relationships, donor–acceptor matching criteria and aspects of device physics are discussed. Finally, we consider the remaining challenges and promising future directions for the NFA OSCs field. Non-fullerene acceptors have been widely used in organic solar cells over the past 3 years. This Review focuses on the two most promising classes of non-fullerene acceptors — rylene diimide-based materials and fused-ring electron acceptors — and discusses structure–property relationships, donor– acceptor matching criteria and device physics, as well as future research directions for the field.

Non-fullerene acceptors for organic solar cells

A novel non-fullerene electron acceptor (ITIC) that overcomes some of the shortcomings of fullerene acceptors, for example, weak absorption in the visible spectral region and limited energy-level variability, is designed and synthesized. Fullerene-free polymer solar cells (PSCs) based on the ITIC acceptor are demonstrated to exhibit power conversion effi ciencies of up to 6.8%, a record for fullerene-free PSCs.

An electron acceptor challenging fullerenes for efficient polymer solar cells.

A nonfullerene electron acceptor (IEIC) based on indaceno[1,2-b:5,6-b′]dithiophene and 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile was designed and synthesized. IEIC exhibited good thermal stability, strong absorption in the 500–750 nm region with an extinction coefficient of 1.1 × 105 M−1 cm−1 at 672 nm, deep LUMO energy level (−3.82 eV) close to those of fullerenes, and a relatively high electron mobility of 2.1 × 10−4 cm2 V−1 s−1. Fullerene-free polymer solar cells (PSCs) based on the blends of the IEIC acceptor and a low-bandgap polymer donor PTB7-TH, using a perylene diimide derivative as a cathode interlayer, showed power conversion efficiencies (PCEs) of up to 6.31%, which is among the best PCEs reported for fullerene-free PSCs.

High-performance fullerene-free polymer solar cells with 6.31% efficiency

A novel planar acceptor IDT-2BR was designed and synthesized. Polymer solar cells (PSCs) based on P3HT:IDT-2BR blended films gave power conversion efficiencies of up to 5.12%, which are much higher than that of PC61BM-based control devices (3.71%) and the highest values reported for P3HT-based fullerene-free PSCs.

A planar electron acceptor for efficient polymer solar cells

A novel small molecule based on indacenodithiophene and 1,1-dicyanomethylene-3-indanone was synthesized and used as an electron acceptor in solution processed organic solar cells, which exhibited a power conversion efficiency as high as 3.93%.

An electron acceptor based on indacenodithiophene and 1,1-dicyanomethylene-3-indanone for fullerene-free organic solar cells

Four A-D-A type small molecules using 4,4,9,9-tetrakis(4-hexylphenyl)- indaceno[1,2-b:5,6-b′]dithiophene as central building block, bithiophene or terthiophene as π-bridges, alkyl cyanoacetate or rhodanine as end acceptor groups were synthesized and investigated as electron donors in solution-processed organic solar cells (OSCs). These molecules showed excellent thermal stability with decomposition temperatures over 360 °C, relatively low HOMO levels of −5.18 to −5.22 eV, and strong optical absorption from 350 to 670 nm with high molar extinction coefficient of 1.1 × 105 to 1.6 × 105 M–1 cm–1 in chloroform solution. OSCs based on blends of these molecules and PC71BM achieved average power conversion efficiencies of 2.32 to 5.09% (the best 5.32%) after thermal annealing. The effects of thiophene bridge length and end acceptor groups on absorption, energy level, charge transport, morphology, and photovoltaic properties of the molecules were investigated.

Huitao Bai

Papers

An electron acceptor challenging fullerenes for efficient polymer solar cells.

High-performance fullerene-free polymer solar cells with 6.31% efficiency

A planar electron acceptor for efficient polymer solar cells

An electron acceptor based on indacenodithiophene and 1,1-dicyanomethylene-3-indanone for fullerene-free organic solar cells

Acceptor–Donor–Acceptor Small Molecules Based on Indacenodithiophene for Efficient Organic Solar Cells