Single‐Material Organic Solar Cells Based on Small Molecule Homojunctions: An Outdated Concept or a New Challenge for the Chemistry and Physics of Organic Photovoltaics?

Abstract

Single‐material organic solar cells (SMOSCs) are on the forefront of research on organic photovoltaics (OPV). The generic term of SMOSCs encompasses a large variety of chemical structures implying very different basic concepts. Polydisperse «double cable» polymers and oligomers with acceptor groups linked to the conjugated backbone by a flexible spacer and donor–acceptor block copolymers are at present, the most investigated and efficient systems with spectacular progress in conversion efficiency achieved in the past 2–3 years. However, besides this mainstream SMOSCs research, a few recent publications describe OPV cells constituted of homojunctions based on small π‐conjugated molecules. While the process of charge generation in such systems is still a matter of debate due in particular to the possible direct photogeneration of charge–carriers, devices with significant performance have been recently reported. After a brief overview of the most recent advances on the various types of SMOSCs, recent remarkable results on homojunction OPV cells based on small π‐conjugated molecules are discussed in order to highlight the potential fundamental and technological interest of this emerging field of research.

Molecular dyads with non-fused electron acceptor backbones for single-component organic solar cells

“…9,10 As a straightforward and drastic strategy, the single component photoactive layer has been employed to address the inherent instability issues of binary BHJ architecture, in which D and A are covalently combined in one molecule by exible insulation or rigid p-conjugated linkers. [11][12][13] Apart from the remarkable stability of single component OSCs (SCOSCs), a considerably simplied lm fabrication process is also a unique advantage for industrial application. More specially, in SCOSCs, the exciton generation and dissociation would occur at one sole molecular architecture, denitely erasing the issue regarding limitations of the short exciton diffusion length.…”

“…More specially, in SCOSCs, the exciton generation and dissociation would occur at one sole molecular architecture, definitely erasing the issue regarding limitations of the short exciton diffusion length. 11…”

Achieving 12.6% Efficiency in Single‐Component Organic Solar Cells Processed from Nonhalogenated Solvents

“…There are three types of SCOSCs have been developed, [ 25 ] mainly including molecular dyads, [ 17,21 ] double‐cable conjugated polymers, [ 20,26 ] and conjugated block copolymers (CBCs). [ 27–29 ] Compared with the molecular dyads and double‐cable conjugated polymers, CBCs are capable of relatively simple synthesis (i.e., one‐pot polymerization), and various types of CBCs were developed with an impressive achievement of PCEs over 6%.…”

“…[24] As a consequence, the highest PCE of SCOSCs is still far lagging behind that of the reported BHJ OSCs. [5] There are three types of SCOSCs have been developed, [25] mainly including molecular dyads, [17,21] double-cable conjugated polymers, [20,26] and conjugated block copolymers (CBCs). [27][28][29]…”

Structure–properties of small donor–acceptor molecules for homojunction single-material organic solar cells

“…25,26 Homojunction organic solar cells (HOSCs) based on small molecules are the ultimate stage of simplification of SMOSCs and hence of OSCs. 27 Although the low efficiency of primitive HOSCs 4 has severely hampered research in this direction, some recent reports suggest of renewal of interest in this of topic. [28][29][30][31][32][33][34][35][36][37] Research on HOSCs is a high-risk challenge but the knowledge accumulated during a half-century of OSC research represents a valuable intellectual capital which makes it possible to consider the problem on new bases.…”