Extended exciton lifetime via TADF material as energy donor in layer-by-layer all-polymer solar cells exhibiting 18.35 % efficiency

초록

Layer-by-layer all-polymer solar cells (LbL-APSCs) were constructed based on wide bandgap polymer PBQx-TCl as donor and narrow bandgap polymer PY-DT as acceptor. According to the Beer-Lambert law, most of photogenerated excitons will be generated in the donor layer near ITO electrode in LbL-APSCs. The utilization of excitons near ITO electrode should be great challenge for obtaining efficient LbL-APSCs due to the limited exciton diffusion distance. The power conversion efficiency (PCE) of LbL-APSCs can be improved from 17.35 % to 18.35 % by incorporating 0.3 wt% 4CzIPN, accompanied with simultaneously increased short-circuit current density of 25.09 mA cm- 2, open-circuit voltage (VOC) of 0.974 V and fill factor of 75.08 %. The energy loss (Eloss) in normal LbL-APSCs and inverted LbL-APSCs can be decreased from 0.513 eV to 0.503 eV and from 0.519 eV to 0.511 eV by incorporating 0.3 wt% 4CzIPN in PY-DT layer, resulting in the enhancement of VOC. The photoluminescence lifetime of PBQx-TCl and PY-DT can be prolonged from 182 ps to 295 ps and from 274 ps to 438 ps by incorporating 0.3 wt% 4CzIPN in PBQx-TCl layer or PY-DT layer, indicating the efficient energy transfer from 4CzIPN to PBQx-TCl and PY-DT. This work indicates that thermally activated delayed fluorescence material as an energy donor has great potential in constructing high-performance LbL-APSCs.

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