Excitons dynamics of 1-chloronaphthalene added P3HT:PC61BM solar cells

- 1-chloronaphthalene(CN) can enhance the efficiency of P3HT:PCBM Solar Cells from charge photogeneration and recombination.
- The enhanced fraction of CT states with CN added comes from the more crystalline P3HT phases and the slower CT states.
- Mobile charges decay of blend with CN added indicates reduced recombination losses from early time recombination.

The charge photogeneration and recombination are comprehensively investigated in blend films based on poly(3-hexylthiophene) (P3HT) as an electron donor and [6,6]-phenyl-C 61-butyric acid methyl ester (PC61BM) as an electron accepter. Transient absorption spectroscopy (TAS) together with absorption, photoluminescence (PL) are used respectively to measure optical properties of these blend films. In this paper, we demonstrate that solvent additive 1-chloronaphthalene (CN) has a unique influence on improving the performance of P3HT:PC61BM heterojunction solar cell. It is observed that the absorption of additive-added blends has a higher intensity and is red-shifted than that of the P3HT:PC61BM blend. The PL intensity increases which suggest that the conjugation length increases or the domain size of P3HT increases. Large domains with serious phase separation influence the interface area between P3HT and PC61BM. Excitons are generated in both the P3HT phase and the PC61BM phase. In all the film blends with or without additive, strongly bound interfacial CT states are formed by a large fraction of the excitons indicating geminate recombination may occur. It is demonstrated that in the blend with CN added the enhanced fraction of CT states comes from the more crystalline P3HT phases and the slower CT states and mobile charges decay indicates reduced recombination losses from early time recombination.