Phenothiazine-based small-molecule organic solar cells with power conversion efficiency over 7% and open circuit voltage of about 1.0 V using solvent vapor annealing

Abstract

We have used two unsymmetrical small molecules, named phenothiazine 1 and 2 with a D-A-D-π-D configuration, where phenothiazine is used as a central unit, triphenylamine is used as a terminal unit and TCBD and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD are used as an acceptor between the phenothiazine and triphenylamine units, as a small molecule donor along with PCBM as an acceptor for solution processed bulk heterojunction solar cells. The variation of acceptors in the phenothiazine derivatives makes an exciting change in the photophysical and electrochemical properties, hole mobility and therefore photovoltaic performance. The optimized device based on phenothiazine 2 exhibited a high power conversion efficiency of 7.35% (J = 11.98 mA cm, V = 0.99 V and FF = 0.62), while the device based on phenothiazine 1 showed a low PCE of 4.81% (J = 8.73 mA cm, V = 0.95 V and FF = 0.58) after solvent vapour annealing (SVA) treatment. The higher value of power conversion efficiency of the 2 based devices irrespective of the processing conditions may be related to the broader absorption and lower band gap of 2 as compared to 1. The improvement in the SVA treated active layer may be related to the enhanced crystallinity, molecular ordering and aggregation and shorter π-π stacking distance of the small molecule donors.

Synthesis and Properties of New Multiple TCNE Adducts from Dialkynyl‐N‐(het)arylpyrroles

“…The wide scope of this “click” reaction has been recently covered in comprehensive reviews , . The push‐pull properties stemming from these donor‐substituted TCBD moieties have recently found successful applications in photovoltaic devices , . Indeed, optimal charge‐transfer is a critical parameter for the design of sensitizers for solar energy applications.…”

Structure-induced optoelectronic properties of phenothiazine-based materials

“…In a similar study, Sharma and coworkers prepared two unsymmetrical small molecules 31 and 32 with a D-A-D-p-D architecture, where the central PTZ unit is connected to terminal triphenylamine via electron-withdrawing 1,1,4,4-tetracyanobutadiene and cyclohexa-2,5-diene-1,4-diylidene moieties. 51 The optimized OSCs with 32 as the active layer exhibited a high PCE of 7.35%, while the devices with 31 showed a low PCE of 4.81%. Revoju et al further examined the effect of varying the side chain and p-conjugation length on three A-A-D-A-A type PTZ-based small molecules.…”

Promoting Photocatalytic Hydrogen Evolution Activity of Graphitic Carbon Nitride with Hole‐Transfer Agents

“…Different derivatives of PTZ were also studied for the photocatalytic HER by combining them with a TiO 2 photocatalyst [13] . In addition, PTZ‐based molecules were successfully explored as hole‐transfer agents to improve the efficiency of solar cells [14] . Two main factors directly control the use of PTZ as an ideal hole‐transfer agent during the photocatalytic process: (i) one‐electron oxidation of PTZ to form the cationic radical (PTZ .+ ) with high stability and (ii) thermodynamically favorable hole transfer from the VB of g ‐CN [1.47 V vs. normal hydrogen electrode (NHE)] to the highest occupied molecular orbital (HOMO) of PTZ (0.9 V vs. NHE) [15] …”

“…[13] In addition, PTZ-based molecules were successfully explored as hole-transfer agents to improve the efficiency of solar cells. [14] Two main factors directly control the use of PTZ as an ideal hole-transfer agent during the photocatalytic process: (i) one-electron oxidation of PTZ to form the cationic radical (PTZ * + ) with high stability and (ii) thermodynamically favorable hole transfer from the VB of g-CN [1.47 V vs. normal hydrogen electrode (NHE)] to the highest occupied molecular orbital (HOMO) of PTZ (0.9 V vs. NHE). [15] Although Durrant and co-workers reported that the photophysics of g-CN materials are similar to that of inorganic semiconductors, [16] the role of the hole-transport agents (HTAs) on the photocatalytic properties of g-CN or, in a broader context, to photoactive organic polymers remains unexplored.…”