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abstract: Summary Recently, non fullerene n type organic semiconductors have attracted significant attention as acceptors in organic photovoltaics (OPVs) due to their great potential to realize high power conversion efficiencies. The rational design of the central fused ring unit of these acceptor molecules is crucial to maximize device performance. Here, we report a new class of non fullerene acceptor, Y6, that employs a ladder type electron deficient core based central fused ring (dithienothiophen[3.2 b] pyrrolobenzothiadiazole) with a benzothiadiazole (BT) core to fine tune its absorption and electron affinity. OPVs made from Y6 in conventional and inverted architectures each exhibited a high efficiency of 15.7% measured in two separate labs. Inverted device structures were certified at Enli Tech Laboratory demonstrated an efficiency of 14.9% We further observed that the Y6 based devices maintain a high efficiency of 13.6% with an active layer thickness of 300 nm. The electron deficient core based fused ring reported in this work opens a new door in the molecular design of high performance acceptors for OPVs.
author_names: Jun Yuan

Yunqiang Zhang

Liuyang Zhou

Guichuan Zhang

Hin-Lap Yip

Tsz-Ki Lau

Xinhui Lu

Can Zhu

Hongjian Peng

Paul A Johnson

Mario Leclerc

Yong Cao

Jacek Ulanski

Yongfang Li

Yingping Zou
title: Single Junction Organic Solar Cell with over 15% Efficiency Using Fused Ring Acceptor with Electron Deficient Core
venue: Joule
year: 2019

author_names: Qishi Liu

Yufan Jiang

Ke Jin

Jianqiang Qin

Jingui Xu

Wenting Li

Ji Xiong

Jinfeng Liu

Zuo Xiao

Kuan Sun

Shangfeng Yang

Xiaotao Zhang

Liming Ding
title: 18% Efficiency organic solar cells
year: 2020

abstract: Besides broadening of the absorption spectrum, modulating molecular energy levels, and other well studied properties, a stronger intramolecular electron push pull effect also affords other advantages in nonfullerene acceptors. A strong push pull effect improves the dipole moment of the wings in IT 4F over IT M and results in a lower miscibility than IT M when blended with PBDB TF. This feature leads to higher domain purity in the PBDB TF:IT 4F blend and makes a contribution to the better photovoltaic performance. Moreover, the strong push pull effect also decreases the vibrational relaxation, which makes IT 4F more promising than IT M in reducing the energetic loss of organic solar cells. Above all, a power conversion efficiency of 13.7% is recorded in PBDB TF:IT 4F based devices.
author_names: Wanning Li

Long Ye

Sunsun Li

Huifeng Yao

Harald W Ade

Jianhui Hou
title: A High Efficiency Organic Solar Cell Enabled by the Strong Intramolecular Electron Push Pull Effect of the Nonfullerene Acceptor.
venue: Advanced materials
year: 2018

abstract: With rapid development for tens of years, organic solar cells (OSCs) have attracted much attention for their potential in practical applications. As an important photovoltaic parameter, the fill factor (FF) of OSCs stands for the effectiveness of charge generation and collection, which significantly depends on the properties of the interlayer and active layer. Here, a facile and effective strategy to improve the FF through hole transporting layer (HTL) modification is demonstrated. By mixing WOx nanoparticles with a poly(3,4 ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) emulsion, the surface free energy of the HTL is improved and the morphology of the active layer is optimized. Benefiting from increased carrier lifetime, a device based on WOx :PEDOT:PSS HTL exhibits a boosted performance with an FF of 80.79% and power conversion efficiency of 14.57% PCE. The results are certified by the National Institute of Metrology (NIM) which, to date, are the highest values in this field with certification. This work offers a simple and viable option of HTL modification to realize highly efficient OSCs.
author_names: Zhong Zheng

Qin Hu

Shaoqing Zhang

Dongyang Zhang

Jianqiu Wang

Shenkun Xie

Rong Wang

Yunpeng Qin

Wanning Li

Ling Hong

Ningning Liang

Feng Liu

Yuan Zhang

Zhixiang Wei

Zhiyong Tang

Thomas P Russell

Jianhui Hou

Huiqiong Zhou
title: A Highly Efficient Non Fullerene Organic Solar Cell with a Fill Factor over 0.80 Enabled by a Fine Tuned Hole Transporting Layer.
venue: Advanced materials
year: 2018

abstract: Nowadays, organic solar cells (OSCs) with Y6 and its derivatives as electron acceptors provide the highest efficiencies among the studied binary OSCs. To further improve the performances of OSCs, the fabrication of ternary OSCs (TOSCs) is a convenient strategy. Essentially, morphology control and the trade off between voltage and photocurrent are the main critical issues in TOSCs. Herein, we address these problems by constructing TOSCs where an alloy like composite is formed between Y6 and a newly designed derivative, BTP M. Employing an electron pushing methyl substituent as a replacement for the electron withdrawing F atoms on Y6, BTP M shows higher energy levels and lower crystallinity than Y6. As a result, the obtained Y6:BTP M alloy can simultaneously optimize energy levels to reduce energy loss as well as the morphologies of the active layers to favor photocurrent generation, leading to an enhanced open circuit voltage (Voc) of 0.875 V together with a larger short circuit current density (Jsc) of 26.56 mA cm 2 for TOSCs based on the polymer donor PM6 and Y6:BTP M acceptor alloy. Consequently, a best efficiency of 17.03% is achieved for the corresponding TOSCs, which is among the best values for single junction OSCs. In addition, our TOSCs also exhibit good thickness tolerance, and can reach 14.23% efficiency even though the active layer is as thick as 300 nm.
author_names: Lingling Zhan

Shuixing Li

Tsz-Ki Lau

Yong Cui

Xinhui Lu

Minmin Shi

Changzhi Li

Hanying Li

Jianhui Hou

Hongzheng Chen
title: Over 17% efficiency ternary organic solar cells enabled by two non fullerene acceptors working in an alloy like model
year: 2020

abstract: Stability through oxysalts The stability of organic inorganic perovskite solar cells is limited by degradation from oxygen and water. Yang et al. show that in situ reaction of perovskites with sulfate or phosphate ions can create thin, strongly bonded lead oxysalt layers that protect defect sites. This layer also boosts charge carrier lifetimes that lead to a power conversion efficiency of more than 20% Encapsulated devices maintained about 97% of this efficiency with simulated solar irradiation for nearly 2 months at a realistic operation temperature of 65degC. Science, this issue p. 473 Thin lead oxysalt layers passivate hybrid perovskite surfaces under an ambient atmosphere and enhance solar cell efficiency. We show that converting the surfaces of lead halide perovskite to water insoluble lead (II) oxysalt through reaction with sulfate or phosphate ions can effectively stabilize the perovskite surface and bulk material. These capping lead oxysalt thin layers enhance the water resistance of the perovskite films by forming strong chemical bonds. The wide bandgap lead oxysalt layers also reduce the defect density on the perovskite surfaces by passivating undercoordinated surface lead centers, which are defect nucleating sites. Formation of the lead oxysalt layer increases the carrier recombination lifetime and boosts the efficiency of the solar cells to 21.1% Encapsulated devices stabilized by the lead oxysalt layers maintain 96.8% of their initial efficiency after operation at maximum power point under simulated air mass (AM) 1.5 G irradiation for 1200 hours at 65degC.
author_names: Shuang Yang

Shangshang Chen

Edoardo Mosconi

Yanjun Fang

Xun Xiao

Congcong Wang

Yu Jie Zhou

Zhenhua Yu

Jingjing Zhao

Yongli Gao

Filippo De Angelis

Jinsong Huang
title: Stabilizing halide perovskite surfaces for solar cell operation with wide bandgap lead oxysalts
venue: Science
year: 2019

abstract: The remarkable development in photovoltaic (PV) technologies over the past 5 years calls for a renewed assessment of their performance and potential for future progress. Here, we analyse the progress in cells and modules based on single crystalline GaAs, Si, GaInP and InP, multicrystalline Si as well as thin films of polycrystalline CdTe and CuInxGa1 xSe2. In addition, we analyse the PV developments of the more recently emerged lead halide perovskites together with notable improvements in sustainable chalcogenides, organic PVs and quantum dots technologies. In addition to power conversion efficiencies, we consider many of the factors that affect power output for each cell type and note improvements in control over the optoelectronic quality of PV relevant materials and interfaces and the discovery of new material properties. By comparing PV cell parameters across technologies, we appraise how far each technology may progress in the near future. Although accurate or revolutionary developments cannot be predicted, cross fertilization between technologies often occurs, making achievements in one cell type an indicator of evolutionary developments in others. This knowledge transfer is timely, as the development of metal halide perovskites is helping to unite previously disparate, technology focused strands of PV research.Nearly all types of solar photovoltaic cells and technologies have developed dramatically, especially in the past 5 years. Here, we critically compare the different types of photovoltaic technologies, analyse the performance of the different cells and appraise possibilities for future technological progress.
author_names: Pabitra K Nayak

Suhas Mahesh

Henry J Snaith

David Cahen
title: Photovoltaic solar cell technologies: analysing the state of the art
venue: Nature Reviews Materials
year: 2019

abstract: Stabilization of the crystal phase of inorganic/organic lead halide perovskites is critical for their high performance optoelectronic devices. However, due to the highly ionic nature of perovskite crystals, even phase stabilized polycrystalline perovskites can undergo undesirable phase transitions when exposed to a destabilizing environment. While various surface passivating agents have been developed to improve the device performance of perovskite solar cells, conventional deposition methods using a protic polar solvent, mainly isopropyl alcohol (IPA) results in a destabilization of the underlying perovskite layer and an undesirable degradation of device properties. We demonstrate the hidden role of IPA in surface treatments and develop a strategy in which the passivating agent is deposited without destabilizing the high quality perovskite underlayer. This strategy maximizes and stabilizes device performance by suppressing the formation of the perovskite d phase and amorphous phase during surface treatment, which is observed using conventional methods. Our strategy also effectively passivates surface and grain boundary defects, minimizing non radiative recombination sites, and preventing carrier quenching at the perovskite interface. This results in an open circuit voltage loss of only ~340 mV, a champion device with a power conversion efficiency of 23.4% from a reverse current voltage scan, a device with a record certified stabilized PCE of 22.6% and enhanced operational stability. In addition, our perovskite solar cell exhibits an electroluminescence external quantum efficiency up to 8.9%
author_names: Jason J Yoo

Sarah Wieghold

Melany Sponseller

Matthew R Chua

Sophie N Bertram

Noor Titan Putri Hartono

Jason S Tresback

Eric C Hansen

Juan-Pablo Correa-Baena

Vladimir Bulovic

Tonio Buonassisi

Seong Sik Shin

Moungi G Bawendi
title: An interface stabilized perovskite solar cell with high stabilized efficiency and low voltage loss
year: 2019

abstract: Over the past few years, non fullerene organic solar cells have been a focus of research and their power conversion efficiencies have been improved dramatically from about 6 to over 14 In addition to innovations in non fullerene acceptors, the ongoing development of polymer donors has contributed significantly to the rapid progress of non fullerene organic solar cell performance. This Minireview highlights the polymer donors that enable high performance non fullerene organic solar cells. We show the impressive photovoltaic devices results achieved by some of important classes of conjugated polymer systems in non fullerene organic solar cells. We discuss the molecular design strategies as far as developing matching polymer donors for non fullerene acceptors. We conclude with a brief summary and outlook for advances in donor polymers required for commercialization.
author_names: Huiting Fu

Zhaohui Wang

Yanming Sun
title: Polymer Donors for High Performance Non Fullerene Organic Solar Cells.
venue: Angewandte Chemie
year: 2019

abstract: Energy loss within organic solar cells (OSCs) is undesirable as it reduces cell efficiency 1 4 In particular, non radiative recombination loss 3 and energetic disorder 5 which are closely related to the tail states below the band edge and the overall photon energy loss, need to be minimized to improve cell performance. Here, we report how the use of a small molecule acceptor with torsion free molecular conformation can achieve a very low degree of energetic disorder and mitigate energy loss in OSCs. The resulting single junction OSC has an energy loss due to non radiative recombination of just 0.17 eV and a high power conversion efficiency of up to 16.54% (certified as 15.89% by the National Renewable Energy Laboratory) The findings take studies of organic photovoltaics deeper into a new regime, beyond the limits of energetic disorder and large energy offset for charge generation. An organic solar cell designed with minimal energetic disorder exhibits very low energy loss due to non radiative recombination and highly efficient operation.
author_names: Shan Liu

Jun Yuan

Wanyuan Deng

Mei Luo

Yuan Xie

Quanbin Liang

Yingping Zou

Zhicai He

Hongbin Wu

Yong Cao
title: High efficiency organic solar cells with low non radiative recombination loss and low energetic disorder
year: 2020