Optimization and performance enhancement of conjugated polymer and fullerene derivatives based bulk heterojunction photovoltaic cells: weight ratios of donor and acceptor, anodic buffer layer thickness and heat treatment

Abstract

In this research, we systematically investigated and optimized the performance of photovoltaic cells based on P3HT: PCBM in different conditions. The applied conditions to these cells include the change in the weight ratio of the donor (P3HT) to the acceptor (PCBM), the thickness of the anodic buffer layer (MoO3), and the annealing temperature of the active layer. An accurate correlation between these physical parameters is essential for the better performance of bulk heterojunction photovoltaic cells. At each step of the experiment, the power conversion efficiency, short-circuit current density, and fill factor increased. Laboratory evidence suggests that a cell fabricated from the same weight ratio of the donor and acceptor (1:1) has a better performance than other proportions. The power conversion efficiency in this case was 3.12%. In addition, the optimum thickness of 7 nm was determined for MoO3 as anodic buffer layer, in which the power conversion efficiency of the cell increased to 3.52%. By investigating the different annealing temperatures of the active layer to optimize the polymer photovoltaic cell, it was observed that at annealing temperature of 140 °C, the cell demonstrated better performance and the power conversion efficiency of the cell increased to 4.74%. Finally, the correlation between morphology changes of the active layer surface and the efficiency of the cell were investigated.