Synergistic Effects of Electric-Field-Assisted Annealing and Thermal Annealing in Bulk-Heterojunction Solar Cells

Abstract

We propose an optimum low-temperature-based annealing procedure for semicrystalline donor-fullerene solar cells that is well-suited for plastic and flexible substrates. This proposed alternate strategy utilizes an external electric field (EF) across the bulk heterojunction (BHJ) film during processing at a desired temperature. This processing technique is studied for different molecular weights of the donor in the BHJ blend films. The films indicate an increase in interchain interactions of the semicrystalline polymer chains and an enhancement in hole mobility with EF-assisted annealing treatment. Besides being a controlled method, this processing technique is capable of yielding solar cell devices with performance equivalent to or better than those obtained using plain thermal procedures.

Enhanced Stability and Optimized Morphology Induced by Electric‐Field‐Assisted Annealing of Bulk Heterojunction Solar Cells

“…These results are consistent with our earlier studies of GIWAXS where EF(+) treatment was carried out on P3HT: PC 70 BM BHJ films. [6a] The XRD peak of polymer donor around Q value of 0.31 A −1 , corresponds to the alkyl interchain interaction (100) . The lower intensity of the PTB7‐Th peak reflects the amorphous nature of the donor polymer.…”

“…EFTA‐treated devices exhibit nominal efficiency and higher stability when compared with control devices. The EFTA treatment involves an application of external DC electric field (EF) during TA of active layer . Earlier studies on EFTA treatment were focused on semicrystalline donor polymer; primarily, semicrystalline donor (P3HT‐based BHJs).…”

“…Earlier studies from our laboratory of the EFTA treatment focused on the effects of molecular weight or varying chain length of P3HT in P3HT:PC 70 BM devices. [6a] It was observed that the optimum EF strength at which the maximum device performance was dependent on the molecular weight of the donor. In the Out‐Of‐Plane‐GIWAXS spectra, PC 70 BM peak around 2 θ of 18 ° ( Q ≈ 1.3 A −1 ) was shown to decrease as the EF strength was increased during the treatment.…”

Elongated Nanodomains and Molecular Intermixing Induced Doping in Organic Photovoltaic Active Layers with Electric Field Treatment

“…Among the various synthesis parameters [6][7][8][9][10][11][12][13][14], the effects of the application of electric field during synthesis or as a postproduction treatment have shown improvements in the PCE [11,[15][16][17][18][19][20][21][22]. A better understanding of the electric field treatment will provide great insights on further improving the OPVC performance.…”

“…Other factors were also discussed in literature, such as the elimination of the nano-domains (better intermolecular mixing) [32] or the rougher surfaces for better contact [24]. In some works, the electric field dependence experiments showed that there exists a certain optimized electric field strength for the optimal OPVC performance [20][21][22]. This observation indicates that the electric field treatment may induce both positive and negative impacts on the OPVC performance.…”