A Simple and Effective Modification of PCBM for Use as an Electron Acceptor in Efficient Bulk Heterojunction Solar Cells

Abstract

[6,6]‐phenyl‐C‐61‐butyric acid methyl ester (PCBM) and poly(3‐hexylthiophene) (P3HT) are the most widely used acceptor and donor materials, respectively, in polymer solar cells (PSCs). However, the low LUMO (lowest unoccupied molecular orbital) energy level of PCBM limits the open circuit voltage (Voc) of the PSCs based on P3HT. Herein a simple, low‐cost and effective approach of modifying PCBM and improving its absorption is reported which can be extended to all fullerene derivatives with an ester structure. In particular, PCBM is hydrolyzed to carboxylic acid and then converted to the corresponding carbonyl chloride. The latter is condensed with 4‐nitro‐4’‐hydroxy‐α‐cyanostilbene to afford the modified fullerene F. It is more soluble than PCBM in common organic solvents due to the increase of the organic moiety. Both solutions and thin films of F show stronger absorption than PCBM in the range of 250–900 nm. The electrochemical properties and electronic energy levels of F and PCBM are measured by cyclic voltammetry. The LUMO energy level of F is 0.25 eV higher than that of PCBM. The PSCs based on P3HT with F as an acceptor shows a higher Voc of 0.86 V and a short circuit current (Jsc) of 8.5 mA cm−2, resulting in a power conversion efficiency (PCE) of 4.23%, while the PSC based on P3HT:PCBM shows a PCE of about 2.93% under the same conditions. The results indicate that the modified PCBM, i.e., F, is an excellent acceptor for PSC based on bulk heterojunction active layers. A maximum overall PCE of 5.25% is achieved with the PSC based on the P3HT:F blend deposited from a mixture of solvents (chloroform/acetone) and subsequent thermal annealing at 120 °C.

Confined organization of fullerene units along high polymer chains

“…These characteristic absorption features represent free methanofullerene derivatives in solution, similar to those reported for PCBM. 50 The spectrum of 4a (m ¼ 12), however, showed the same absorption features but the absorbance from 400 to 550 nm increased, making the peak at 430 nm less sharp compared to that of 3a. For 4b, a shorter spacer (m ¼ 6) made the peak at 430 nm even broader.…”

Complementary study on the electrical and structural properties of poly(3-alkylthiophene) and its copolymers synthesized on ITO by electrochemical impedance and Raman spectroscopy

“…The ITO presents appropriate work function value to organic materials, i.e. it has a good ability to collect electrons generated by electron donors, allowing this property to vary according to changes in its active surface [13][14][15][16][17].…”

Light‐Harvesting Materials for Organic Electronics

“…In this regard Mikroyannidis et al [56] described recently a simple and effective modification of PCBM by a two-step reaction. This modified PCBM (25, Fig.…”