Search

How to improve charge transport properties and reduce energy losses are the two main challenges of organic solar cells (OSCs). Herein, a new device fabrication strategy that combines the layer‐by‐layer (LBL) method and a quaternary active layer is demonstrated to realize highly efficient photovoltaic performance of the OSCs based on PM6:PM7/Y6:O1‐2F. The introduction of the second donor, PM7, forms a cascade energy‐level alignment with PM6 that facilitates effective charge transfer. The second acceptor, O1‐2F, which is poorly miscible with the donors, helps to reduce the miscibility between the donors and acceptors, and thus delivers a more desirable vertical phase separation of the active layer. Furthermore, the alloy acceptor of O1‐2F and Y6 can optimize the horizontal and vertical morphology of the active layer, forming an effective charge separation and continuous charge transport channel. As a result, the PM6:PM7/Y6:O1‐2F system shows a distinct increase in charge mobility and a reduced nonradiative loss ΔVnr of 0.231 V compared to the PM6/Y6 system, achieving a high‐power conversion efficiency of 18.23%. The results indicate that the quaternary LBL OSCs are promising for future large‐scale and industrial manufacture of the OSCs. [ABSTRACT FROM AUTHOR]

The high‐performance organic solar cells (OSCs) tend to choose the polymers with high molecular weight as donors, which easily produce good crystallinity to facilitate intermolecular charge transfer. However, these polymers usually accompanied by the low solubility and synthetic difficulty, increasing batch‐to‐batch variations. The proposal of conjugated mesopolymers (molar mass (Mn) in 1–10 kDa) can overcome these problems. Herein, a new mesopolymer, MePBDFClH as donor material is designed and synthesized, and firstly applied in OSCs. As a comparison, other lower molecular weight mesopolymer of MePBDFClL and higher molecular weight polymer of PBDFCl with same structure are also prepared and investigated. Because of its appropriate phase separation and miscibility in the blend film, the MePBDFClH exhibits the highest power conversion efficiency (PCE) of 15.06% among the three materials. Meanwhile, the champion PCE is a new record for benzo[1,2‐b:4,5‐b′]difuran‐based photovoltaic materials. Importantly, comparing to the pronounced PCE decrease of polymer PBDFCl by about 12%, a slightly PCE difference for mespolymer MePBDFClL is only less than 5%, reducing the batch‐to‐batch variation. This work not only suggests that the benzo[1,2‐b:4,5‐b′]difuran unit is a promising electron‐donating core but also shows that the mesopolymers have great potentials to produce the low‐differentiated and high‐performance organic photovoltaic materials. [ABSTRACT FROM AUTHOR]

Rational design and synthesis of new small‐molecule donors are critically important to achieve highly efficient small‐molecule organic solar cells (SM‐OSCs) with desirable device stability. Herein, two new acceptor–donor–acceptor (A–D–A) structured small‐molecule donor materials SM‐DTBDT and SM‐BDT with dithieno[2,3‐d:2′,3′‐d′]benzo[1,2‐b:4,5‐b′]dithiophene (DTBDT) and benzodithiophene (BDT) as the core D‐units are designed and synthesized, respectively. After thermal annealing treatment, the power conversion efficiencies (PCEs) of the SM‐DTBDT‐ and SM‐BDT‐based devices with Y8 as acceptor material reach 12.45% and 10.68%, respectively. The main reason for the different device performance can be ascribed to the different crystallinity and morphology features of the small‐molecule donor:Y8 blend films. Compared with the SM‐BDT:Y8 blend films, the SM‐DTBDT:Y8 blend films show a smoother surface, more uniform phase separation, mixed edge‐on and face‐on orientations, and enhanced crystallinity, resulting in the more efficient exciton dissociation and charge transport. In addition, it is observed that the SM‐DTBDT‐based devices also exhibit better stability. This work shows that fine‐tuning the center units of small‐molecule donors can not only increase the photovoltaic performance but can also be an effective method to improve the device stability. [ABSTRACT FROM AUTHOR]