Ternary strategy and material modification for high efficiency organic solar cell

Abstract

Organic solar cells (OSCs) have gained plenty of attention due to their unique properties, including light-weight, environmental friendly, semi-transparent, solution-processable and low cost. However, the problems such as low Voc, low charge mobilities, and recombination losses challenge the efficiency improvement of OSCs. Exploring new ternary material systems and modifying the involved materials could be the promising approaches to overcome these issues. In this thesis. I mainly focused on introducing the third component to the OSCs and modifying materials to achieve efficient OSCs. Fullerenes have high charge mobilities and introducing of PCBM as the third component can achieve better device efficiencies. Here, we added the PCBM to the high efficiency OSCs, and the device V_OC can be effectively promoted and both the Jsc and FF are also concurrently increased. A high efficiency of 16.7% were obtained with PM6:Y6:PC₇₁BM. We also investigate their optoelectronic properties and morphology and evacuate the mechanism of the improvement from the third component. Modifying the acceptor materials is another strategy to improve the OSC performance. we introduced a strategy of modifing Y6-series NFA via combining the branched alkyl chain and alkoxy chain substitution of the outer thiophene unit in Y6. Due to the upshifted LUMO, the Y6-O2BO based binary device can yield a much-enhanced V_OC of 0.96 V and a PCE of 16.2%. Ternary devices by mixing Y6 with Y6-O2BO were fabricated and the V_OC could be elevated progressively with the increasing fraction of Y6-O2BO. A maximum efficiency of 17.5% of the ternary device was achieved. Modifying the polymer donor is also important for OSCs. We also focused on the application of BDF units in D18 polymer donor and synthesized a new polymer D18-Fu. Y6-1O was chosen as the acceptor. The D18-Fu-based OSC achieved an excellent PCE of 16.38%, When PC₇₁BM was used as the third component, ternary device obtained a PCE of 17.07% with an excellent FF of 80.4%. The D18-Fu show more compact π-π stacking in the OOP direction, thus benefit the charge transport and results in higher FF.

Date of Award	2022
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	He YAN (Supervisor) & Zhiyong FAN (Supervisor)