TY  - JOUR
A1  - Kegelmann, Lukas
A1  - Wolff, Christian Michael
A1  - Awino, Celline
A1  - Lang, Felix
A1  - Unger, Eva L.
A1  - Korte, Lars
A1  - Dittrich, Thomas
A1  - Neher, Dieter
A1  - Rech, Bernd
A1  - Albrecht, Steve
T1  - It Takes Two to Tango-Double-Layer Selective Contacts in Perovskite Solar Cells for Improved Device Performance and Reduced Hysteresis
JF  - ACS applied materials & interfaces
N2  - Solar cells made from inorganic organic perovskites have gradually approached market requirements as their efficiency and stability have improved tremendously in recent years. Planar low-temperature processed perovskite solar cells are advantageous for possible large-scale production but are more prone to exhibiting photocurrent hysteresis, especially in the regular n-i-p structure. Here, a systematic characterization of different electron selective contacts with a variety of chemical and electrical properties in planar n-i-p devices processed below 180 degrees C is presented. The inorganic metal oxides TiO2 and SnO2, the organic fullerene derivatives C-60, PCBM, and ICMA, as well as double-layers with a metal oxide/PCBM structure are used as electron transport materials (ETMs). Perovskite layers deposited atop, the different ETMs with the herein applied fabrication method show a similar morphology according to scanning electron microscopy. Further, surface photovoltage spectroscopy measurements indicate comparable perovskite absorber qualities on all ETMs, except TiO2, which shows a more prominent influence of defect states. Transient photoluminescence studies together with current voltage scans over a broad range of scan speeds reveal faster charge extraction, less pronounced hysteresis effects, and higher efficiencies for devices with fullerene compared to those with metal oxide ETMs. Beyond this, only double-layer ETM structures substantially diminish hysteresis effects for all performed scan speeds and strongly enhance the power conversion efficiency up to a champion stabilized value of 18.0%. The results indicate reduced recombination losses for a double-layer TiO2/PCBM contact design: First, a reduction of shunt paths through the fullerene to the ITO layer. Second, an improved hole blocking by the wide band gap metal oxide. Third, decreased transport losses due to an energetically more favorable contact, as implied by photoelectron spectroscopy measurements. The herein demonstrated improvements of multilayer selective contacts may serve as a general design guideline for perovskite solar cells.
KW  - perovskite solar cell
KW  - electron contact
KW  - double-layer
KW  - regular planar architecture
KW  - hysteresis
KW  - fullerene
KW  - metal oxide
Y1  - 2017
U6  - https://doi.org/10.1021/acsami.7b00900
SN  - 1944-8244
VL  - 9
SP  - 17246
EP  - 17256
PB  - American Chemical Society
CY  - Washington
ER  -