Toward Morphological Stabilization in Polymer Bulk Heterojunction Solar Cells by Crosslinking Using an Additive

A new approach to enhance performance and to stabilize active layer morphology by introducing a reacting processing additive, i.e., ditert butyl peroxide (DTBP), to the donor (P3HT) and acceptor (PCBM) solution with minimal disturbance in the packing of conjugated polymer is presented. Effects of DTBP contents and thermal annealing time on the performance of photovoltaic cells are investigated. Compared with the control device, the optimized device with 0.5 wt% DTBP exhibits enhanced performance with a J _sc of (10.44 ± 0.13) mA/cm ² , a fill factor of (57.61 ± 1.56)%, and a power conversion efficiency of (3.82 ± 0.11)%, which increases by 10%, 26%, and 33%, respectively. The enhanced mobility of carriers is attributed to the DTBP additive-induced decomposition, which leads to the rough morphology of the active layer, and to the more effective interfacial area formed between the P3HT and PCBM regions. We envisage the direct crosslinking of the alkyl chain of P3HT results in the formation of 3-D polymeric networks, which limits the conformational dynamics of P3HT and indirectly hinders the diffusion of PCBM, thus enabling efficient and more stable photovoltaic devices. Therefore, the large-scale phase separation between P3HT and PCBM in the active layer can be effectively suppressed.