Abstract
AbstractCrystallizable, high‐mobility conjugated polymers have been employed as secondary donor materials in ternary polymer solar cells in order to improve device efficiency by broadening their spectral response range and enhancing charge dissociation and transport. Here, contrasting effects of two crystallizable polymers, namely, PffBT4T‐2OD and PDPP2TBT, in determining the efficiency improvements in PTB7‐Th:PC71BM host blends are demonstrated. A notable power conversion efficiency of 11% can be obtained by introducing 10% PffBT4T‐2OD (relative to PTB7‐Th), while the efficiency of PDPP2TBT‐incorporated ternary devices decreases dramatically despite an enhancement in hole mobility and light absorption. Blend morphology studies suggest that both PffBT4T‐2OD and PDPP2TBT are well dissolved within the host PTB7‐Th phase and facilitate an increased degree of phase separation between polymer and fullerene domains. While negligible charge transfer is determined in binary blends of each polymer mixture, effective energy transfer is identified from PffBT4T‐2OD to PTB7‐Th that contributes to an improvement in ternary blend device efficiency. In contrast, energy transfer from PTB7‐Th to PDPP2TBT worsens the efficiency of the ternary device due to inefficient charge dissociation between PDPP2TBT and PC71BM.
Highlights
Recent work has shown that semi-crystalline conjugated macromolecules or small molecules are effective third components when preparing efficient ternary solar cells. [18,19,20] For example, both the crystallinity and face-on preferential polymer orientation in PTB7-Th:PC71BM binary blends can be simultaneously enhanced via the addition of a highly crystalline small molecule p-DTS(FBTTH2)2, resulting in a high Power conversation efficiency (PCE) of 10.5%.[21]
The weak External quantum efficiency (EQE) spectra in the wavelength range from 780 to 900 nm in Figure 1f indicate a part of photocurrent derived from PDPP2TBT:PC71BM[37, 38,55], the contribution of this cell is limited as the photocurrent generation between PDPP2TBT and PC71BM is inefficient, restricting the overall PCE of the PTB7-Th:PDPP2TBT:PC71BM ternary blend
Morphology studies suggest that the incorporation of PffBT4T-2OD and PDPP2TBT into the PTB7Th:PC71BM blends obstructs the crystallization of these crystallizable additives, and both PffBT4T-2OD and PDPP2TBT were located in the PTB7-Th domains, increasing the average sizes of the phase-separated polymer and fullerene domains
Summary
Over the past ten years, promising progress has been made in organic photovoltaics (OPVs) by developing new electron donors and acceptors,[1,2] controlling and optimizing the nanoscale morphology[3,4,5] and via interfacial engineering of the device architectures.[6,7] Power conversation efficiency (PCE) metrics for this technology stand at 13% for lab-scale single junction and tandem devices.[8,9] Ternary photovoltaic blends,[10,11,12,13,14,15] prepared by incorporating a third component into the donor:acceptor active layer, have emerged as a promising strategy for realizing further improvements in PCE by enhancing device spectral response and charge collection efficiency This method is favorable as it removes the time-consuming and expensive process of synthesizing new conjugated polymers, in addition to the complicated manufacturing steps that are associated with tandem solar cell fabrication.[16,17]. The addition of an optimum amount of PffBT4T-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
