Recent Advances in n-Type Polymers for All-Polymer Solar Cells

All-polymer solar cells (all-PSCs) based on n- and p-type polymers have emerged as promising alternatives to fullerene-based solar cells due to their unique advantages such as good chemical and electronic adjustability, and better thermal and photochemical stabilities. Rapid advances have been made in the development of n-type polymers consisting of various electron acceptor units for all-PSCs. So far, more than 200 n-type polymer acceptors have been reported. In the last seven years, the power conversion efficiency (PCE) of all-PSCs rapidly increased and has now surpassed 10%, meaning they are approaching the performance of state-of-the-art solar cells using fullerene derivatives as acceptors. This review discusses the design criteria, synthesis, and structure-property relationships of n-type polymers that have been used in all-PSCs. Additionally, it highlights the recent progress toward photovoltaic performance enhancement of binary, ternary, and tandem all-PSCs. Finally, the challenges and prospects for further development of all-PSCs are briefly considered.

Utilizing Benzotriazole and Indacenodithiophene Units to Construct Both Polymeric Donor and Small Molecular Acceptors to Realize Organic Solar Cells With High Open-Circuit Voltages Beyond 1.2 V

Devolopment of organic solar cells with high open-circuit voltage (V_OC) and power conversion efficiency (PCE) simutaniously plays a significant role, but there is no guideline how to choose the suitable photovoltaic material combinations. In our previous work, we developed "the Same-Acceptor-Strategy" (SAS), by utilizing the same electron-accepting segment to construct both polymeric donor and small molecular acceptor. In this study, we further expend SAS to use both the same electron-accepting and electron-donating units to design the material combination. The p-type polymer of PIDT-DTffBTA is designed by inserting conjugated bridge between indacenodithiophene (IDT) and fluorinated benzotriazole (BTA), while the n-type small molecules of BTAx (x = 1, 2, 3) are obtained by introducing different end-capped groups to BTA-IDT-BTA backbone. PIDT-DTffBTA: BTAx (x = 1-3) based photovolatic devices can realize high V_OC of 1.21-1.37 V with the very small voltage loss (0.55-0.60 V), while only the PIDT-DTffBTA: BTA3 based device possesses the enough driving force for efficient hole and electron transfer and yields the optimal PCE of 5.67%, which is among the highest value for organic solar cells (OSCs) with a V_OC beyond 1.20 V reported so far. Our results provide a simple and effective method to obtain fullerene-free OSCs with a high V_OC and PCE.

Improved color rendering index of low band gap semi-transparent polymer solar cells using one-dimensional photonic crystals

Improved CRI and PCE were achieved by introducing 1DPCs as a wavelength-dependent filter on top of semi-transparent polymer solar cells.

Structure–property relationship in fluorene-based polymer films obtained by electropolymerization of 4,4′-(9-fluorenylidene)-dianiline

For the first time, the electropolymerization of 4,4′-(9-fluorenylidene)-dianiline and physico-chemical properties of the obtained polymer films are reported.