[25p-E206-1~9] 12.5 Organic solar cells

△ [25p-E206-3] Quantifying the Optimal Thickness in Polymer:Fullerene Solar Cells from the Analysis of Charge Transport Dynamics and Photoabsorption

〇Shaoxian Li¹, Fumiya Hamada¹, Ryosuke Nishikubo^1,2, Akinori Saeki^1,2 (1.Osaka Univ., 2.ICS-OTRI)

Keywords:organic solar cell, charge transport dynamics, device optimal thickness

The optimal photoactive layer thickness (L_opt) of bulk heterojunction (BHJ) organic solar cells (OSCs) is typically below 200 nm, which is unlikely suitable for large scale production. To increase L_opt, a deeper understanding on L_opt is indispensable. Here we propose a semi-empirical model for quantifying L_opt in OSCs considering the carrier transport length, space charge effect and photoabsorption. Three polymer:fullerene OSCs (P3HT, PffBT4T, and PCPDTBT blended with PCBM) were used to validate this model. Simultaneous measurements of time-of-flight (TOF) and time-resolved microwave conductivity (TRMC) revealed the electron/hole mobility relaxation and effective carrier diffusion length. The space charge effect on L_opt was examined by the electron/hole mobility balance. The photoabsorption effect was incorporated by the effective absorption coefficient under AM 1.5G. Using this model, the calculated L_opt of these BHJs was consistent with the experimental values. This model’s effectiveness was further supported by the solar cell capacitance simulator (SCAPS) calculations. We provided a feasible method and insight for quantifying L_opt in OSCs.