Proceedings Article | 10 September 2019
KEYWORDS: Perovskite, Organic semiconductors, Semiconductors, Heterojunctions, Optoelectronics, Photovoltaics, Light emitting diodes, Transistors, Photodetectors, Molecules
The emergence of hybrid organic inorganic perovskites (HOIPs) perovskites, with their higher charge carrier mobilities and tunable bandgap, coupled with low-cost processability, has opened new avenues of research in optoelectronic applications. Various devices based on HOIPs, including photovoltaics, light-emitting diodes, transistors or photodetectors have been reported. Here, we explore the photocurrent properties in heterostructures consisting of small molecule semiconductors and HOIPs. Bilayer devices can use bandgap alignment to improve carrier separation and collection. The HOIP CH3NH3PbI3-xClx was the primary photoactive layer and electron transport layer, while the hole transport layer was 2,8-Difluoro-6,13-Bis(triisopropylsilylethynyl) anthradithiophene (diF-TIPS-ADT). We found that the responsivity of the bilayer device was six times greater than neat perovskite film, reaching values as high as 5.1 A/W, and detectivity more than doubled, to 2.9*10^11 Jones. We further tuned the interfacial processes by altering the microstructure of the organic semiconductor layer and evaluated the photocurrent response. We found that treatment of the gold contacts with (2,3,4,5,6)-Pentafluorothiophenol (PFBT) resulted in large grains within the organic semiconductor. Consequently, responsivity was over 15 times greater than that of the neat perovskite film, reaching values of 13.7 A/W, and detectivity improved by 8 times to 8.4*10^11 Jones. Grazing-incidence X-ray diffraction measurements indicate that diF-TIPS-ADT is preferentially oriented with its (001) plane parallel to the substrate in both sample types. The observed performance improvement thus cannot originate from differences in the interfacial coupling related to molecular orientation. Instead, we believe differences in trapping at grain boundaries is responsible for the changes in charge generation efficiency.
