Improved performance of polymer solar cells by using inorganic, organic, and doped cathode buffer layers

The interface between the active layer and the electrode is one of the most critical factors that could affect the device performance of polymer solar cells. In this work, based on the typical poly（3-hexylthiophene）：[6,6]-phenyl C61-butyric acid methyl ester （P3HT：PCBM） polymer solar cell, we studied the effect of the cathode buffer layer （CBL） between the top metal electrode and the active layer on the device performance. Several inorganic and organic materials commonly used as the electron injection layer in an organic light-emitting diode （OLED） were employed as the CBL in the P3HT：PCBM polymer solar cells. Our results demonstrate that the inorganic and organic materials like Cs2CO3, bathophenanthroline （Bphen）, and 8-hydroxyquinolatolithium （Liq） can be used as CBL to efficiently improve the device performance of the P3HT：PCBM polymer solar cells. The P3HT：PCBM devices employed various CBLs possess power conversion efficiencies （PCEs） of 3.0%-3.3%, which are ca. 50% improved compared to that of the device without CBL. Furthermore, by using the doped organic materials Bphen：Cs2CO3 and Bphen：Liq as the CBL, the PCE of the P3HT：PCBM device will be further improved to 3.5%, which is ca. 70% higher than that of the device without a CBL and ca. 10% increased compared with that of the devices with a neat inorganic or organic CBL.

Efficiency enhancement in DIBSQ：PC71BM organic photovoltaic cells by using Liq-doped Bphen as a cathode buffer layer

We have improved the photovoltaic performance of 2,4-bis[4-（N,N- diisobutylamino）-2,6-dihydroxyphenyl] squaraine：[6,6]-phenyl C71-butyric acid methyl ester （DIBSQ：PC71BM） organic photovoltaic （OPV） cells via incorporating Liq-doped Bphen （Bphen-Liq） as a cathode buffer layer （CBL）. Based on the Bphen-Liq CBL, a DIBSQ：PC71BM OPV cell possessed an optimal power conversion efficiency of 4.90%, which was 13% and 60% higher than those of the devices with neat Bphen as CBL and without CBL, respectively. The enhancement of the device performance could be attributed to the enhanced electron mobility and improved electrode/active layer contact and thus the improved photocurrent extraction by incorporating the Bphen-Liq CBL. Light-intensity dependent device performance analysis indicates that the incorporating of the Bphen-Liq CBL can remarkably improve the charge transport of the DIBSQ：PC71BM OPV cell and thus decrease the recombination losses of the device, resulting in enhanced device performance. Our finding indicates that the doped Bphen-Liq CBL has great potential for high-performance solution-processed small-molecule OPVs.