Surfactant n-dopant in cathode interlayer or electron transport layer for polymer or perovskite solar cells with improving performance

Abstract

We present a simple and effective method to improve the performance and stability of organic and perovskite solar cells by the incorporation of room temperature solution-processed cetyltrimethylammonium bromide (CTAB)-doped zirconium oxide (ZrO x ) as cathode interlayer. Via anion-induced electron transfer between the bromide anions (Br−) of CTAB and ZrO x in the solid state, electrical conductivity was significantly improved from 4.3×109 to 2.9×10−5 S cm−1 CTAB doping lifts up work function of ZrO x -coated Ag electrode from 4.21 to 3.72 eV, which facilitates a better ohmic contact to a polymer (PTB7 or PDPP-TBT):fullerene (PC 61 BM or PC 71 BM) bulk heterojunction or perovskite (CH 3 NH 3 PbI 3 )/PC 61 BM bilayer and a higher built-in potential of the device. These are the causes for higher short-circuit current (J SC ) higher open-circuit voltage (V oc ), and hence better power conversion efficiency (PCE), 9.3 vs. 3.2% (PTB7), 2.5 vs. 0.6% (PDPP-TBT), 15.9 vs. 7.1% (perovskite) Surfactant CTABdoped PC 61 BM works as well in p-type perovskite solar cells. The combination of the ion pair interaction (from PC 61 BM radical anion and cetyltrimethylammonium cation) and long floppy cetyl group of CTAB reduces the aggregation of PC 61 BM and promotes the coverage of the PC 61 BM thin film onto the perovskite layer. Our fabricated p-type perovskite solar cells deliver PCE as high as 17.11%, which is much better than CH 3 NH 3 PbI 3 /PC 61 BM devices without CTAB dopant (PCE is only 2.15%). Moreover, CTAB-doped perovskite solar cells showed little hysteresis and retained 80% of the initial PCE after 360 hours of shelf-storage, where devices were under ambient conditions (30°C, ∼ 60% relative humidity) without extra package or encapsulation.