Enhanced Organic Solar Cells Efficiency through Additive Electronic and Electro-optic Effects Resulting from Doping a Polymer Hole Transport Layer

摘要

We demonstrate that blending fluorinated molecules in PEDOT:PSS holetransport layers (HTL) induces charge transfers which impact on both chargeextraction and photogeneration within organic photovoltaic (OPV) devices. OPVsfabricated with modified HTL and two photoactive polymer blends ledsystematically to power conversion efficiencies (PCE) increases, withPTB7:PC70BM blend exhibiting PCE of ~ 8.3 %, i.e. ~ 15 % increase compared topristine HTL devices. A reduced device-to-device characteristics variations wasalso noticed when fluorinated additives were used to modify the PEDOT:PSS.Shading lights onto the effect of HTL fluorination, we show that the morphologyof the polymer:PCBM blends remains surprisingly unaffected by the fluorinatedHTL surface energy but that, instead, the OPVs are impacted not only by the HTLelectronic properties (work function, dipole layer, open circuit voltage,charge transfer dynamic) but also by alteration of the complex refractiveindices (photogeneration, short circuit current density, external quantumefficiencies, electro-optic modelling). Both mechanisms find their origin influorination induced charge transfers. This work points towards fluorination asa promising strategy toward combining both external quantum efficiencymodulation and power conversion efficiency enhancement in OPVs. Chargetransfers could also be used more broadly to tune the optical constants andelectric field distribution, as well as to reduce interfacial chargerecombinations within OPVs.