Small is Powerful: Recent Progress in Solution‐Processed Small Molecule Solar Cells

Abstract

Over the last 5 years, research on the synthesis, device engineering, and device physics of solution‐processed small molecule solar cells (SMSCs) has rapidly expanded. Improvements in molecular design and emergent device processing techniques have helped solution‐processed SMSCs overcome earlier difficulties in controlling active layer morphology, such that many systems are now at—or approaching—10% power conversion efficiency. In this review, details of the highest performing blend systems are presented in order to identify key trends and provide perspective on current progress in the field. Among the best systems, a planarized molecular structure is prevalent, which can be achieved using large fused‐ring moieties, intermolecular non‐bonding interactions, and side chain engineering. To obtain efficient devices, the highest performing systems have been optimized through the careful combination of thermal and solvent annealing procedures. Even without additional processing, some systems have been able to obtain interconnected morphologies and efficient charge generation and charge transport. Ultimately, the design of more efficient materials also requires additional understanding of the device physics and loss mechanisms. After highlighting what is known to date on processes limiting device efficiency, an outlook on the most important challenges remaining to the field is provided.

Charge Separation and Triplet Exciton Formation Pathways in Small-Molecule Solar Cells as Studied by Time-Resolved EPR Spectroscopy

“…8 Recently BHJs that incorporate solution processed small molecule donors in place of the polymer have become increasingly competitive, with PCEs of 10.1 % now reported. 6, 9–10 …”

The Dawn of Single Material Organic Solar Cells

“…The control of the nanoscale morphology of the interface is the key to the fabrication of BHJs. [32][33][34][35][36][37][38][39] Whereas the first examples of molecular donor such as thiophene or PPV oligomers or acenes possess a homogeneous electronic structure, [38] molecular donors of second generation are based on combinations of D and A building blocks in order to create an internal charge transfer which at the same time improves the light-harvesting properties of the material and increases the cell voltage. Conjugated polymers have been for a long time the unique class of D materials for BHJs.…”

“…Conjugated polymers have been for a long time the unique class of D materials for BHJs. [36] Owing to high electron mobility and isotropic charge transport, fullerenes derivatives have become the standard acceptor materials for OPV. [27][28][29] On the other hand, soluble derivatives of fullerenes C 60 and C 70 , namely [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM) and PC 71 BM have been the standard acceptor materials for many years.…”

Rationalizing Small‐Molecule Donor Design toward High‐Performance Organic Solar Cells: Perspective from Molecular Architectures

“…Here, the impact of different molecular architectures (i.e., A-π -D-π -A, D-π-A-π -D and π-A-D-A-π ) of the donors on the interfacial arrangements and electronic processes in small-molecule (SM) OSCs is elucidated by means of multiscale theoretical simulations. [20][21][22][23][24][25][26][27][28] To date, three typical push-pull molecular structures, namely, D-π -A-π -D, π -A-D-A-π , and A-π -D-π -A, have been successfully used as SM donors. [1][2][3][4][5][6][7][8][9] For fullerene-based small-molecule (SM) OSCs, power conversion efficiencies (PCEs) have exceeded 11%, which is in stark contrast to the highest value of 1% in 2006 (Figure 1a).…”

“…[1][2][3][4][5][6][7][8][9] For fullerene-based small-molecule (SM) OSCs, power conversion efficiencies (PCEs) have exceeded 11%, which is in stark contrast to the highest value of 1% in 2006 (Figure 1a). [20][21][22][23][24][25][26][27][28] To date, three typical push-pull molecular structures, namely, D-π -A-π -D, π -A-D-A-π , and A-π -D-π -A, have been successfully used as SM donors. [20][21][22][23][24][25][26][27][28] To date, three typical push-pull molecular structures, namely, D-π -A-π -D, π -A-D-A-π , and A-π -D-π -A, have been successfully used as SM donors.…”