New progress in all-molecular organic solar cells

Energy shortages and environmental pollution have become important factors constraining social and economic development. The use of renewable energy, especially solar energy, is increasingly showing its importance. As a result, more and more solar energy is being developed and utilized, energy conversion efficiency is rising, and the cost of use is decreasing. The main way to use solar energy is solar cells.

The development of solar cell

In 1954, Bell Labs in the United States successfully developed silicon solar cells, which pioneered the research of photoelectric conversion, and the research on solar cells developed rapidly. Originally it focused on inorganic solar cells using single crystal silicon as an active material. In the 1990s, devices such as gallium arsenide, cadmium telluride, and stacked GaInP/GaAs/Ge were developed, which were composed of single crystal, polycrystalline or amorphous films. At present, solar cells are roughly classified into three categories: crystalline silicon solar cells, thin film solar cells, and new solar cells. Crystalline silicon solar cells are further divided into single crystal silicon and polycrystalline silicon solar cells. Thin film solar cells include amorphous silicon solar cells and multi-component solar cells, and new solar cells include organic solar cells, dye-sensitized solar cells, quantum dot solar cells, and hybrid perovskite solar cells.

All small molecule organic solar cell

Recently, Professor Zhang Haoli of Lanzhou University and Professor Xiao Wei of Peking University have made a series of new progress on all-molecular organic solar cells.

All-small-molecule organic solar cells are a new type of organic solar cells with small organic molecules as donor materials and fused ring electron acceptors as acceptor materials. These cells can fully combine small molecule donors and fused ring electron acceptors. The advantages have great research value and application potential. However, such batteries are currently under-researched and have low performance, which is mainly due to the design of small molecule donor materials and the precise regulation of the active layer morphology.

Earlier, the researchers designed two medium optical band gap small molecule donors, BDTTT-DPP and BDTTVT-DPP, to match the narrow optical band gap of the fused ring electron acceptor, and the star fused ring electron acceptor IDIC. The efficiency of blended ASM-OSCs was 5%. Subsequently, the researchers designed two new small molecule donors, DRBDT-TVT and DRBDT-STVT, by extending the conjugated backbone to control molecular energy levels and stacking. The efficiency of ASM-OSCs prepared exceeded 6.5%. Based on the above exploration, the researchers further proposed the design strategy of Dual-Accepting-Unit, designed and synthesized a small molecule donor SBDT-BDD with structure A1-A2-D-A2-A1 type, medium optical band gap and deep HOMO level. Based on SBDT-BDD: IDIC's binary battery can achieve 9.2% efficiency, based on SBDT-BDD: IDIC:PC71BM ternary battery can get 10.9% efficiency, which is one of the highest efficiency of this type of battery.

It was found that PC71BM as a third component can effectively control the morphology of the active layer and synergistically improve the short-circuit current and fill factor of the device. The donor molecular design strategy developed by the researcher with double-suction electron unit has important guiding significance for obtaining the all-molecular cell with superior performance, and provides an effective way for the precise regulation of the active layer morphology of the whole small molecule battery. 

Edited by Suzhou Yacoo Science Co., Ltd.