Synthesis of a Broadly Absorbing Modified PCBM and Application As Electron Acceptor with Poly(3-Hexylthiophene) As Electron Donor in Efficient Bulk Heterojunction Solar Cells

Abstract

A simple and effective modification of PCBM was carried out by a two-step reaction. The modified PCBM, i.e., A was obtained as a mixture of monoadduct and multiadducts arising from the Prato reaction and was soluble in THF. It showed broader and stronger absorption in the visible region of the solar spectrum than PCBM due to the presence of a cyanovinylene 4-nitrophenyl segment. The lowest occupied molecular energy level (LUMO) of A was measured and found that it is higher than that of PCBM by 0.15 eV. The polymer solar cell (PSC) based on the P3HT as the electron donor with A as the electron acceptor shows an open circuit voltage (V oc) of 0.80 V, a short-circuit current (J sc) of 9.0 mA/cm2, and a power conversion efficiency (PCE) of 3.88%, which are higher than those for the PSC based on P3HT:PCBM. The higher PCE for the PSC based on P3HT:A accounts for the increase in both J sc and V oc, due to the increased absorption of A in the visible region and its higher LUMO level. The PCE of the PSC has been further increased to 4.50% and 5.32% when the P3HT:A blend film is cast from mixed solvents and subsequent thermal annealing, respectively. The improvement in PCE is mainly due to the increase in J sc, which has been attributed to the increase in the crystallinity of the film leading to an increase in the hole mobility, which causes a balanced charge transport in the devices.

Effect of preparation parameters on performance of P3HT: PCBM solar cells

“…It is very important to control the film thickness and processing conditions of the active layer, where photons were absorbed to generate excitons, in order to achieve high short-circuit current and power conversion efficiencies (PCE) [4][5][6][7][8][9]. In recent years, new donor and acceptor materials or additive materials have been applied to improve the photoelectric conversion property of photoactive layer by enhancing the capture ability of the donor/ acceptor (D/A) hetero-junctions and optimizing the energy level alignment of interface [10][11][12]. Poly(3-hexylthiophene) (P3HT) is the one of the most commonly used donor materials due to its higher hole transporting ability (10 À 4 -10 À 2 cm 2 V À 1 s À 1 ) and lower band gap.…”

[60]Fullerene‐quinoxaline, benzothiadiazole and benzoselenadiazole based dyads for thermally stable polymer solar cells: anchoring of substituent on fullerene with a poly(3‐hexylthiophene) polymer chain

“…Figure shows the UV–visible absorption spectra of TQT, TBTT, TBST, TQT‐C 60 , TBTT‐C 60 and TBST‐C 60 in o ‐DCB solution. All three chromophoric units, TQT, TBTT and TBST, exhibit two well‐defined absorption bands: the bands in the high energy region correspond to the π–π* transition and the bands in the lower energy region correspond to the intramolecular charge transfer (ICT) interactions between the electron rich and electron deficient groups in the chromophoric units . Upon moving from TQT to TBTT to TBST, the absorption maxima of both lower and higher energy bands (TQT 306 nm, 436 nm; TBTT 316 nm, 466 nm; TBST 324 nm, 500 nm) show a red shift; the intensity of the lower energy bands remains the same while the intensity of the higher energy bands increases, as shown in Fig.…”

Efficient bulk heterojunction photovoltaic devices based on modified PCBM

“…Synthesis of a modified PCBM which is soluble in THF was reported by Mikroyannidis et al [41]. Due to the presence of the cyanovinylene 4-nitrophenyl segment, the modified PCBM showed stronger absorption in the visible region of solar spectrum than PCBM.…”

“…MEH-PPV, PCBM and PEDOT: PSS were purchased from Aldrich Chemicals and used as such. The modified PCBM (MPCBM) was supplied by Prof. Mikroyannidis,University of Patra, Greece and its synthesis was given elsewhere[41]. The chemical structure of the donor (MEH-PPV) and the acceptor (PCBM and Modified PCBM) is shown infig.…”