Abstract
1,8-diiodooctane (DIO) additive is an important method for optimizing the morphology and device performance of polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7)-based polymer solar cells. However, the effect of DIO additive on charge photogeneration dynamics of PTB7-based polymer solar cells is still poorly understood. In this work, the effect of DIO additive on the carrier photogeneration dynamics, as well as device performance of PTB7: [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) solar cells was studied. Bias-dependent photoluminescence (PL) experiments of a neat PTB7 device show that the exciton cannot be dissociated by the electric field in the device within the operating voltage range, but it can be effectively dissociated by the high electric field. PL and time-resolved PL studies show that DIO additive reduces the phase size of PTB7 in the blend film, resulting in an increased exciton dissociation efficiency. The carrier recombination processes were studied by transient absorption, which shows geminate carrier recombination was suppressed in the DIO-treated PTB7:PC71BM device in ultrafast time scale. The increased exciton dissociation efficiency and suppressed carrier recombination in ultrafast time scale play an important role for DIO-treated PTB7:PC71BM solar cells to attain a higher power conversion efficiency.
Highlights
In the past few decades, polymer solar cells (PSCs) have received extensive attention due to their outstanding advantages of high flexibility, low cost, and easy processing [1,2,3,4,5]
Detailed analysis of current density-voltage (J–V) properties found that the DIO-treated morphology of the active layer can significantly reduce the loss of geminate recombination in PTB7:phenyl-C71-butyric acid methyl ester (PC71BM) solar cells [22,23]
For PTB7:PC71BM blend films, both with and without DIO treatment, there is a strong absorption in the range of 300~750 nm due to the complementary absorption PC71BM for PTB7
Summary
In the past few decades, polymer solar cells (PSCs) have received extensive attention due to their outstanding advantages of high flexibility, low cost, and easy processing [1,2,3,4,5]. The binding energy of excitons in PTB7 and the influence of DIO additives on the carrier recombination dynamics, on the dissociation and recombination dynamics of charge-transfer state (CT) in ultrafast time scale, need to be clarified. The study of these questions is helpful to understand the role of DIO additives in the photoelectric conversion processes of the active layer and has a certain guiding significance for the performance optimization of new polymer photovoltaic devices. The effect of DIO additive on the carrier photogeneration and recombination dynamics, as well as device performance of PTB7:PC71BM solar cells, was studied. This work is helpful for understanding the influence of additives on the photoelectric conversion processes of photovoltaic devices
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