Premium
Photogenerated Carrier Mobility Significantly Exceeds Injected Carrier Mobility in Organic Solar Cells
Author(s) -
Melianas Armantas,
Pranculis Vytenis,
Xia Yuxin,
Felekidis Nikolaos,
Inganäs Olle,
Gulbinas Vidmantas,
Kemerink Martijn
Publication year - 2017
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201602143
Subject(s) - thermalisation , materials science , charge carrier , picosecond , electron mobility , chemical physics , polymer , organic solar cell , optoelectronics , charge (physics) , space charge , molecular physics , condensed matter physics , atomic physics , physics , optics , electron , laser , quantum mechanics , composite material
Charge transport in organic photovoltaic (OPV) devices is often characterized by space‐charge limited currents (SCLC). However, this technique only probes the transport of charges residing at quasi‐equilibrium energies in the disorder‐broadened density of states (DOS). In contrast, in an operating OPV device the photogenerated carriers are typically created at higher energies in the DOS, followed by slow thermalization. Here, by ultrafast time‐resolved experiments and simulations it is shown that in disordered polymer/fullerene and polymer/polymer OPVs, the mobility of photogenerated carriers significantly exceeds that of injected carriers probed by SCLC. Time‐resolved charge transport in a polymer/polymer OPV device is measured with exceptionally high (picosecond) time resolution. The essential physics that SCLC fails to capture is that of photogenerated carrier thermalization, which boosts carrier mobility. It is predicted that only for materials with a sufficiently low energetic disorder, thermalization effects on carrier transport can be neglected. For a typical device thickness of 100 nm, the limiting energetic disorder is σ ≈71 (56) meV for maximum‐power point (short‐circuit) conditions, depending on the error one is willing to accept. As in typical OPV materials the disorder is usually larger, the results question the validity of the SCLC method to describe operating OPVs.