Abstract
In this work, we studied influence of post thermal annealing on the performance and charge photogeneration processes of PffBT4T-2OD/PC71BM solar cells. As-prepared device exhibits a high-power conversion efficiency of 9.5%, much higher than that after thermal annealing. To understand this phenomenon, we studied charge photogeneration processes in these solar cells by means of time resolved spectroscopy. We associate the degradation of solar cell performance with the reduction of exciton dissociation efficiency and with increased bimolecular recombination of photogenerated charges as a result of annealing. We correlate the generation of localized PffBT4T-2OD polarons observed via spectro-electrochemical measurements with enhancement of the bimolecular charge recombination of annealed solar cells.
Highlights
Polymer solar cells belong to the third-generation solar cell with a number of advantages such as light weight and flexibility, low cost, easy processing for mass production and so on [1,2,3,4]
-quaterthiophen-5,5000 -diyl)] (PffBT4T-2OD) (Figure 1) is a crystallizable polymer with a high hole mobility, which can be manipulated to form an optimal structure for charge photogeneration in bulk heterojunction solar cells [9,10,11,12,13,14,15]
We have studied an effect of thermal annealing on the performance and charge dynamics in PffBT4T-2OD/PC71 BM solar cells
Summary
Polymer solar cells belong to the third-generation solar cell with a number of advantages such as light weight and flexibility, low cost, easy processing for mass production and so on [1,2,3,4]. PCE of PffBT4T-2OD based binary and ternary solar cells has exceeded 10% [9,10,13,15] In these studies, it has been claimed that the interface engineering is required to achieve high PCE to control the morphology of active layer. Thermal annealing is an important method for regulating the morphology of bulk heterojunction polymer solar cells, and has become an essential option for optimizing the device efficiency and performance. PffBT4T-2OD/PC71 BM solar cells, the correlation between the device performance and the dynamics of photogenerated charges is not settled yet. We have studied an effect of thermal annealing on the performance and charge dynamics in PffBT4T-2OD/PC71 BM solar cells. Higher exciton dissociation rate and lower bimolecular recombination result in a higher power conversion efficiency of unannealed device comparing to the thermal annealed ones
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