Molecular Lock Induced by Chloroplatinic Acid Doping of PEDOT:PSS for High-Performance Organic Photovoltaics

In organic photovoltaics (OPVs), the mechanical contact between charge transport layers and photoactive layer can influence the electrical contact that facilitates carrier collection. Unfortunately, the mechanical contact at the interface is rarely discussed in the OPV context. Herein, we report a distinct molecular locking effect that occurs between the donor molecules in the photoactive layer and the hole transport layer (HTL). This is achieved by doping chloroplatinic acid into poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate). The "molecular lock" at the interface leads to denser distribution and more ordered assembling of PM6 donor molecules close to the HTL. Consequently, the trap-assisted recombination in the cell is greatly suppressed, and the carrier lifetime is prolonged by more than 2 times. Together with the elevated charge carrier collection probability, a high fill factor of 77% and a power conversion efficiency of 16.5% are achieved in the PM6:Y6-based OPVs. This study provides a feasible way to boost the device performance by reinforcing the interfacial interaction between the HTL and photoactive layer

Design of All-Small-Molecule Organic Solar Cells Approaching 14% Efficiency via Isometric Terminal Alkyl Chain Engineering

Morphology is crucial to determining the photovoltaic performance of organic solar cells (OSCs). However, manipulating morphology involving only small-molecule donors and acceptors is extremely challenging. Herein, a simple terminal alkyl chain engineering process is introduced to fine-tune the morphology towards high-performance all-small-molecule (ASM) OSCs. We successfully chose a chlorinated two-dimension benzo[1,2-b:4,5-b′]dithiophene (BDT) central unit and two isomeric alkyl cyanoacetate as the end-capped moieties to conveniently synthesize two isomeric small-molecule donors, namely, BT-RO-Cl and BT-REH-Cl, each bearing linear n-octyl (O) as the terminal alkyl chain and another branched 2-ethylhexyl (EH) as the terminal alkyl chain. The terminal alkyl chain engineering process provided BT-RO-Cl with 13.35% efficiency and BT-REH-Cl with 13.90% efficiency ASM OSCs, both with Y6 as the electron acceptor. The successful performance resulted from uniform phase separation and the favorable combination of face-on and edge-on molecular stacking of blended small-molecule donors and acceptors, which formed a fluent 3D transport channel and thus delivered high and balanced carrier mobilities. These findings demonstrate that alkyl chain engineering can finely control the morphology of ASM OSCs, and provides an alternative for the optimal design of small-molecule materials towards high-performance ASM OSCs

19.31% binary organic solar cell and low non-radiative recombination enabled by non-monotonic intermediate state transition

Non-radiative recombination loss suppression is critical for boosting performance of organic solar cells. Here, the authors regulate self-organization of bulk-heterojunction in a non-monotonic manner, and achieve device efficiency over 19% with low non-radiative recombination loss down to 0.168 eV

All-Small-Molecule Organic Solar Cells with an Ordered Liquid Crystalline Donor

The crystallinity and intermolecular interaction among small molecules are enhanced in order to achieve reasonable phase segregation between the donor and acceptor in all-small-molecule organic solar cells (ASM OSCs). By substituting an alkyl side chain with a chlorine (Cl) atom on the original benzodithiophene terthiophene rhodanine (BTR) molecule, the new small molecular donor, namely BTR-Cl, processes a more ordered liquid crystalline property, down-shifted molecular energy levels, and higher crystallinity. When blended with a non-fullerene acceptor Y6, which has a complementary absorption profile and well-matched energy levels but no liquid crystalline property, a prominent phase separation and optimal film morphology are obtained. As a result, a record-high power conversion efficiency (PCE) of 13.6% is achieved, taking a large step forward in ASM OSCs. Our results highlight the importance of crystallinity to phase separation, suggesting the great promise of liquid crystalline materials in OSCs

Rational molecular and device design enables organic solar cells approaching 20% efficiency

Abstract For organic solar cells to be competitive, the light-absorbing molecules should simultaneously satisfy multiple key requirements, including weak-absorption charge transfer state, high dielectric constant, suitable surface energy, proper crystallinity, etc. However, the systematic design rule in molecules to achieve the abovementioned goals is rarely studied. In this work, guided by theoretical calculation, we present a rational design of non-fullerene acceptor o-BTP-eC9, with distinct photoelectric properties compared to benchmark BTP-eC9. o-BTP-eC9 based device has uplifted charge transfer state, therefore significantly reducing the energy loss by 41 meV and showing excellent power conversion efficiency of 18.7%. Moreover, the new guest acceptor o-BTP-eC9 has excellent miscibility, crystallinity, and energy level compatibility with BTP-eC9, which enables an efficiency of 19.9% (19.5% certified) in PM6:BTP-C9:o-BTP-eC9 based ternary system with enhanced operational stability

Rational molecular and device design enables organic solar cells approaching 20% efficiency.

For organic solar cells to be competitive, the light-absorbing molecules should simultaneously satisfy multiple key requirements, including weak-absorption charge transfer state, high dielectric constant, suitable surface energy, proper crystallinity, etc. However, the systematic design rule in molecules to achieve the abovementioned goals is rarely studied. In this work, guided by theoretical calculation, we present a rational design of non-fullerene acceptor o-BTP-eC9, with distinct photoelectric properties compared to benchmark BTP-eC9. o-BTP-eC9 based device has uplifted charge transfer state, therefore significantly reducing the energy loss by 41 meV and showing excellent power conversion efficiency of 18.7%. Moreover, the new guest acceptor o-BTP-eC9 has excellent miscibility, crystallinity, and energy level compatibility with BTP-eC9, which enables an efficiency of 19.9% (19.5% certified) in PM6:BTP-C9:o-BTP-eC9 based ternary system with enhanced operational stability

Artificial Intelligence Designer for Highly-Efficient Organic Photovoltaic Materials

Designing efficient organic photovoltaic (OPV) materials purposefully is still challenging and time-consuming. It is of paramount importance in material development to identify basic functional units that play the key roles in material performance and subsequently establish the substructure-property relationship. Herein, we describe an automatic design framework based on an in-house designed La FREMD Fingerprint and machine learning (ML) algorithms for highly efficient OPV donor molecules. The key building blocks are identified, and a library consisting of 18 960 new molecules is generated within this framework. Through investigating the chemical structures of materials with different performance, a guidance on designing efficient OPV materials is proposed. Furthermore, the most promising candidates exhibit a predicted power conversion efficiency (PCE) value of over 15% when combined with acceptor Y6. Density functional theory (DFT) studies show these candidate materials possess exceptional potential for efficient charge carrier transport. The proposed framework demonstrates the ability to design new materials based on the substructure-property relationship built by ML, which provides an alternative methodology for applying ML in new material discovery