Broadband internal quantum efficiency and absorption enhancement of organic solar cells using a multi-functional layer

Abstract

Here, we report enhanced internal quantum efficiency (IQE) and absorption of small molecular organic solar cells (OSC) in broadband by inserting a multi-functional layer (MFL). An MFL has energy level between main donor and acceptor levels, assisting the charge transport in the active layers. Furthermore, two donors have complementary absorption band yield higher and broader absorption spectra. Experimentally, when $ClAlPc:C_{60}$ was inserted as an MFL on top of $ClAlPc:C_{60}$, the short circuit current ($J_sc$) was improved from $10.35 mA/cm^2$ to $11.63 mA/cm^2$, leading to increase the power conversion efficiency (PCE) from 2.3 % to 2.71 %. In addition, when ClAlPc was inserted as an MFL between CuPc and $C_{60}$ in a trilayer OSC, $J_{sc}$ was enhanced from $5.04 mA/cm^2$ to $6.08 mA/cm^2$, resulting to an increase of the PCE from 1.33 % to 1.69 %.