Bulk heterojunction solar cells with thick active layers and high fill factors enabled by a bithiophene-co-thiazolothiazole push-pull copolymer

Abstract

A push-pull copolymer is presented which can be used in bulk heterojunction (BHJ) solar cells with active layers greater than 200 nm and fill factors above 60%. The efficiencies of most BHJ solar cells are limited by the fact that they have active layers which are between 60 and 110 nm. While this thickness regime enables peak quantum efficiencies (EQE) of 60%–70%, the ability to fabricate thicker devices would increase average EQE values and thus device efficiencies. Discovery of materials which can maintain high performance at large thicknesses will enable higher performance in BHJ hero cells and increase the commercial viability of this technology.

Optically-enhanced performance of polymer solar cells with low concentration of gold nanorods in the anodic buffer layer

“…The architecture of a bulk heterojunction (BHJ) solar cell has demonstrated its potential for enhancing the power conversion efficiency (PCE) by facilitating the excitons dissociation through an interpenetrating network between electron-donor and electron-acceptor materials [2]. Up to now, only 5% PCE has been achieved from a polymer:fullerene BHJ solar cell that comprises poly (3-hexylthiophene-2,5-diyl) (P3HT) as the polymer and [6,6]-phenyl-C 61 -butyric-acid-methyl-ester (PCBM) as the fullerene derivative [3]. The absorption of the active layer (polymer:fullerene layer) is a very important factor for achieving a high photovoltaic (PV)…”

“…The effective reported thickness for the active layer (~ 100-200 nm) [4][5][6] is too low for a complete absorption of the incident light within the absorption range of the active layer.…”

“…Although enlarging the active layer thickness increases its light absorption, the low charge carrier mobilities [5,6] reduce the efficiency of BHJ-OSC due to the increase in the charge carriers recombination and the device series resistance (Rs).…”

4-Terminal Tandem Photovoltaic Cell Using Two Layers of PTB7:PC71BM for Optimal Light Absorption

“…18 The detrimental effects become more apparent for thicker blends by causing a dramatic reduction in fill factor (FF) for the majority of polymers. 19 Recent work explains that for sufficiently thick cells space charge becomes more important because it creates field free regions with low collection efficiency. Doping is suggested as the dominant factor on the space charge and the thickness dependence of the performance.…”

Synthesis and optical and photovoltaic properties of dithienosilole–dithienylpyridine and dithienosilole–pyridine alternate polymers and polymer–B(C6F5)3 complexes

“…[4][5][6][7][8] DTS exhibits enhanced conjugation due to the orbital interaction between the silicon s-bonds and the bithiophene p-system, as well as a highly planar tricyclic structure. 9 Recently, several D-A-type compounds and polymers containing DTS units as the donor were prepared; they were shown to interact efficiently with acceptor groups, such as benzothiadiazole, 10 thiazolothiazole [11][12][13] and thienopyrrolodione, 14 and their applications to high-performance BHJ-type PSCs were explored.…”