Decohesion Kinetics in Polymer Organic Solar Cells

Abstract

We investigate the role of molecular weight (MW) of the photoactive polymer poly(3-hexylthiophene) (P3HT) on the temperature-dependent decohesion kinetics of bulk heterojunction (BHJ) organic solar cells (OSCs). The MW of P3HT has been directly correlated to its carrier field effect mobilities and the ambient temperature also affects OSC in-service performance and P3HT arrangement within the BHJ layer. Under inert conditions, time-dependent decohesion readily occurs within the BHJ layer at loads well below its fracture resistance. We observe that by increasing the MW of P3HT, greater resistance to decohesion is achieved. However, failure consistently occurs within the BHJ layer representing the weakest layer within the device stack. Additionally, it was found that at temperatures below the glass transition temperature (∼41-45 °C), decohesion was characterized by brittle failure via molecular bond rupture. Above the glass transition temperature, decohesion growth occurred by a viscoelastic process in the BHJ layer, leading to a significant degree of viscoelastic deformation. We develop a viscoelastic model based on molecular relaxation to describe the resulting behavior. The study has implications for OSC long-term reliability and device performance, which are important for OSC production and implementation.

Challenge and Solution of Characterizing Glass Transition Temperature for Conjugated Polymers by Differential Scanning Calorimetry

“…Turning to the CPs, we observed a much weaker glass transition both for P3HT and P3(4MP)T, as shown in Figure (b,c), respectively. For P3HT, it features a two‐step transition where the first step with a T g of 11.7 °C (this value shows great agreement the literature reported value of 12–14 °C measured with DSC and DMA …”

“…For P3HT, it features a two-step transition where the first step with a T g of 11.7 C (this value shows great agreement the literature reported value of 12-14 C measured with DSC and DMA. 15,[38][39][40][41] ) is associated with the mobile amorphous fraction and the second one with a T g of 42.2 C is related to the rigid amorphous fraction. This is consistent with previous work by Remy et al 42 Upon tuning the side chain isomerism, surprisingly, P3(4MP)T only gives a one-step transition with a T g of 35.2 C. Such a difference is presumably related to the difference in crystalline morphology and requires further investigation in future.…”

Mechanical integrity of solution-processed perovskite solar cells

“…More robust charge transport layers or replacements must be developed that are not mechanically fragile, hydroscopic, corrosive, or susceptible to delamination from perovskite surfaces.Currently, the most efficient perovskite solar cells utilize organic layers to mediate carrier extraction and charge transport [18]. This places perovskite cells in a similar realm as organicbulk heterojunction solar cells, which, when subjected to thermomechanical analysis, both delaminated readily and exhibited poor layer cohesion [19][20][21][22]. …”

Investigation on the Synthesis and Photocatalytic Property of Uranyl Complexes of the β-Diketonates Biscatecholamide Ligand

“…The peak fitting results of the O 1s and U 4f were shown in Table 4. Because XPS is not a quantitative analysis method, these data could be used for semiquantitative analysis of the distribution of multicomponent [31,32]. As shown in Figure 6(a), it was observed that complexes 1-3 presented six main components O 1s spectra for oxygen functionalities.…”