Organometallic Halide Perovskites: Sharp Optical Absorption Edge and Its Relation to Photovoltaic Performance.
Solar cells based on organometallic halide perovskite absorber layers are emerging as a high-performance photovoltaic technology. Using highly sensitive photothermal deflection and photocurrent spectroscopy, we measure the absorption spectrum of CH3NH3PbI3 perovskite thin films at room temperature. We find a high absorption coefficient with particularly sharp onset. Below the bandgap, the absorption is exponential over more than four decades with an Urbach energy as small as 15 meV, which suggests a well-ordered microstructure. No deep states are found down to the detection limit of ∼1 cm(-1). These results confirm the excellent electronic properties of perovskite thin films, enabling the very high open-circuit voltages reported for perovskite solar cells. Following intentional moisture ingress, we find that the absorption at photon energies below 2.4 eV is strongly reduced, pointing to a compositional change of the material.
†Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL), Maladière 71, Neuchâtel 2000, Switzerland.
Stefaan
S
De Wolf
‡Institute of Physics, Academy of Sciences of the Czech Republic, v. v. i., Cukrovarnická 10, 162 00 Prague, Czech Republic.
Jakub
J
Holovsky
§PV Center, Centre Suisse d'Electronique et de Microtechnique (CSEM), Jacquet Droz 1, Neuchâtel 2000, Switzerland.
Soo-Jin
SJ
Moon
†Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL), Maladière 71, Neuchâtel 2000, Switzerland.
Philipp
P
Löper
†Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL), Maladière 71, Neuchâtel 2000, Switzerland.
Bjoern
B
Niesen
†Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL), Maladière 71, Neuchâtel 2000, Switzerland.|‡Institute of Physics, Academy of Sciences of the Czech Republic, v. v. i., Cukrovarnická 10, 162 00 Prague, Czech Republic.
Martin
M
Ledinsky
†Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL), Maladière 71, Neuchâtel 2000, Switzerland.
Franz-Josef
FJ
Haug
§PV Center, Centre Suisse d'Electronique et de Microtechnique (CSEM), Jacquet Droz 1, Neuchâtel 2000, Switzerland.
Jun-Ho
JH
Yum
†Photovoltaics and Thin-Film Electronics Laboratory, Institute of Microengineering (IMT), Ecole Polytechnique Fédérale de Lausanne (EPFL), Maladière 71, Neuchâtel 2000, Switzerland.|§PV Center, Centre Suisse d'Electronique et de Microtechnique (CSEM), Jacquet Droz 1, Neuchâtel 2000, Switzerland.
Christophe
C
Ballif
Urbach energy; absorption; band edge; bandgap; perovskites; solar cells; stability