Sensitivity of the Drift-Diffusion Approach in Estimating the Power Conversion Efficiency of Bulk Heterojunction Polymer Solar Cells

Abstract

There are numerous theoretical approaches to estimating the power conversion efficiency (PCE) of organic solar cells (OSCs), ranging from the empirical approach to calculations based on general considerations of thermodynamics. Depending on the level of abstraction and model assumptions, the accuracy of PCE estimation and complexity of the calculation can change dramatically. In particular, PCE estimation with a drift-diffusion approach (widely investigated in the literature), strongly depends on the assumptions made for the physical models and optoelectrical properties of semiconducting materials. This has led to a huge deviation as well as complications in the analysis of simulated results aiming to understand the factors limiting the performance of OSCs. In this work, we intend to highlight the complex relation between mobility, exciton dynamics, nanoscale dimension, and loss mechanisms in one framework. Our systematic analysis represents key information on the sensitivity of the drift-diffusion approach, to estimate how physical parameters and physical processes bind the PCE of the device under the influence of structure, contact, and material layer properties. The obtained results ultimately led to recommendations for putting effort into certain properties to get the most out of avoidable losses, presented the impact and importance of modification of material properties, and in particular, recommended to what degree the design of new material could improve OSC performance.

Probing Temperature-Dependent Recombination Kinetics in Polymer:Fullerene Solar Cells by Electric Noise Spectroscopy

“…At room temperature, = 17.6 ± 0.4 × 10 cm 3 ·s −1 and = 4.3 ± 0.1 × 10 cm 3 ·s −1 can be computed for the oDCB and oDCB+THN solvent, respectively. These values are in good agreement with typical recombination factors reported in literature for various organic solar cells [12,50]. As already evidenced, the use of THN reduces the recombination rate at the heterointerface between the donor and the acceptor phases, leading to an increase of the carrier lifetime.…”

“…These techniques give a direct analysis on the charge recombination mechanisms in the polymer:fullerene solar cell. However, they do not provide information on the carrier mobility and, therefore, on the charge transport, which are usually considered inefficient in low mobility materials, such as the P3HT:PCBM blend [12]. In the BHJ solar cell, the charge carrier recombination dynamics is often found to be bimolecular and is described by Langevin's theory [13,14].…”