Understanding the High Performance of over 15% Efficiency in Single‐Junction Bulk Heterojunction Organic Solar Cells

Abstract

The highly efficient single-junction bulk-heterojunction (BHJ) PM6:Y6 system can achieve high open circuit voltages (V OC) while maintaining exceptional fill-factor (FF) and short-circuit current (J SC) values. With a low energetic offset, the blend system was found to exhibit radiative and nonradiative recombination losses that are among the lower reported values in the literature. Recombination and extraction dynamic studies revealed that the device shows moderate nongeminate recombination coupled with exceptional extraction throughout the relevant operating conditions. Several surface and bulk characterization techniques were employed to understand the phase separation, long-range ordering, as well as donor:acceptor (D:A) inter-and intramolecular interactions at an atomic-level resolution. This was achieved using photo-conductive atomic force microscopy (pc-AFM), grazing incidence wide angle x-ray scattering (GIWAXS), and solid-state 19 F Magic-Angle Spinning (MAS) NMR spectroscopy. The synergy of multifaceted characterization and device physics was used to uncover key insights, for the first time, on the structure-property relationships of this high performing BHJ blend. Detailed information about atomically resolved D:A interactions and packing revealed that the high performance of over 15% efficiency in this blend can be correlated to a beneficial morphology that allows high J SC and FF to be retained despite the low energetic offset.

Asymmetric Acceptors with Fluorine and Chlorine Substitution for Organic Solar Cells toward 16.83% Efficiency

“…The development of organic solar cells (OSCs) has experienced a prosperous period in the past decade. [ 1–33 ] Due to their noticeable properties such as semi‐transparency, flexibility and environmental friendliness, the passion of commercialization from researchers and investors is always high. [ 34–38 ] At present, focusing on designing well performed “acceptor‐donor‐acceptor (A‐D‐A)”‐type small molecular acceptors (SMAs), especially the A‐DA'D‐A structured SMAs, is the mainstream of breaking through the bottleneck of power conversion efficiencies (PCEs), for their photovoltaic properties can be easily tuned by simple synthesis steps.…”

Highly Efficient Nonfullerene Organic Photovoltaic Devices with 10% Power Conversion Efficiency Enabled by a Fine‐Tuned and Solution‐Processed Hole‐Transporting Layer

“…For instance, 1) a nonfullerene (NF) material system (so‐called NF‐based OPV) is well known as the next major step forward in OPV technology, and improvements are expected with an energy‐level adjustment by extending the absorption spectrum to increase the short‐circuit current density ( J SC ) or by increasing the built‐in voltage to enhance the open‐circuit voltage ( V OC ). [ 7–17 ] Theoretical PCEs in excess of 20% and 25% for single‐junction and tandem architectures, respectively, have been predicted; [ 18 ] 2) the use of OPV devices in conventional architectures is restricted by stability issues. [ 19,20 ] To improve the stability of the OPV devices, inverted devices have been designed to reverse the electrode positions; furthermore, the unstable materials are replaced as well; [ 21 ] and 3) the entire process used to fabricate the OPV modules should be realized under ambient conditions by using solution coating/printing to minimize the cost.…”

“…[ 22,27 ] However, most of the highly efficient NF‐based OPV devices are typically demonstrated in conventional architectures or have undergone the thermal evaporation of MoO 3 to form the HTL in the inverted structure. [ 7–17,28,29 ] From the perspective of development strategies, combining newly discovered wide‐bandgap polymer donors and small‐bandgap nonfullerene acceptors (NFAs) delivers a high PCE. [ 14,17,30 ] Currently, the best polymer donor reported for collocating NFAs requires an extremely deep highest occupied molecular orbital ( HOMO ) level that is more negative than −5.4 eV to maximize the built‐in voltage of devices.…”

“…[ 14,17,30 ] Currently, the best polymer donor reported for collocating NFAs requires an extremely deep highest occupied molecular orbital ( HOMO ) level that is more negative than −5.4 eV to maximize the built‐in voltage of devices. [ 9–11,16,17,31 ] The low HOMO level of the active layer therefore forms a massive energy barrier between the HOMO of the electron donor and the work function (WF) of PEDOT:PSS (WF ≈ −5.0 eV is mostly reported in the literature), [ 32–34 ] which results in the poor electrical performance of inverted devices. Nevertheless, only a few studies have reported an inverted OPV device using an NF‐based BHJ layer with an alternative solution‐processed HTL for industrial module production.…”

Functionalized rGO Interlayers Improve the Fill Factor and Current Density in PbS QDs-Based Solar Cells

“…The R a correlates with the FF and J SC of the devices and is totally independent from V OC change. V OC is sensitive to the charge carriers' recombination [23,24], which could be enhanced by the rGO incorporation, while the better the film quality the better the QD layer resistance, thus increasing the current and FF.…”