Polymer solar cells power conversion efficiency

Susanna G, Salamandra L, Ciceroni C, Mura F, Brown TM, Reale A, Rossi M, Di Carlo A, Bmnetti F (2015) 8.7 % power conversion efficiency polymer solar cell realized with non-chlorinated solvents. Sol Energy Mater Sol Cells 134 194-198... 

Liang YY, Xu Z, Xia JB, Tsai ST, Wu Y, Li G, Ray C, Yu LP (2010) For the bright future-bulk heterojunction polymer solar cells with power conversion efficiency of 7.4%. Adv Mater 22 E135... 

Physical incorporatiem of phthalocyanines and porphyrins in polymers was mentioned in Chap. 2.1.1 and 2.1.2. Moreover, photovoltaic properties of Schottky bavier solar cells were checked by dispersing metal free Pc in a polymer binder At peak solar power (135 mW/cm ) a power conversion efficiency of 1,2% has been obtained. 

To help the design of optimized polymeric materials for BHJ solar cells, several models have been recently proposed [87-89]. The combination of these models and DFT calculations has recently led to the synthesis of several other poly(2,7-carbazole) derivatives (P17, P19-P22). Symmetric polymers (P17-P19) show better structural organization than asymmetric polymers (P20-P22), resulting in higher hole mobilities and power conversion efficiencies. Moreover, their low HOMO energy levels (ca. (- 5.6)—(— 5.4)eV) provide an excellent air stability and relatively high Voc values (between 0.71-0.96 V). 

Various alternative acceptor components for organic BHJ solar cells have been tried in an attempt to improve cell performance. Fullerene derivatives such as C70 PCBM and Cg4 PCBM have been used in place of Ceo PCBM, because the lower molecular symmetry compared with Ceo PCBM enables stronger light absorption by the fullerene. The C70 PCBM derivatives were relatively successful, leading to 3% power conversion efficiency for devices made with MDMO-PPV polymer (Wienk et al, 2003). The Cg4 derivatives resulted in rather poor device efficiencies, attributed to the unfavourable film morphology resulting from the immiscibility of Cs4 derivatives with typical organic solvents (Kooistra et al, 2006). 

During the last decade polymer solar cells have attracted a steadily increasing interest in both science and industry [7,13-16]. The growing number of scientific pubhcations within this field of research since 1990 impressively demonstrates this fact (Fig. 3) [17]. In fact this surge of interest has corresponded with the accelerating improvements in power conversion efficiency obtained during the last decade, currently reaching about 4-5% [18-21]. 

Table 1 Record power conversion efficiencies and device parameters of polymer solar cells...

Fig. 28 Solar cell parameters for MDMO-PPV PCBM polymer solar cells under slightly elevated temperatures, as expected for realistic operation conditions. Interestingly, the short circuit photocurrent increases with temperature, while the open circuit voltage drops. As a result the power conversion efficiency is maximized for temperatures of 50 (Reprinted with permission from [122], 2001, American Institute of Physics)...

With the prospect of long-term stability [185,188] and the abiUty to print polymer solar cells [188] with power conversion efficiencies of 4-5%, EQEs of over 75%, internal quantum efficiencies approaching unity [194], and fill factors of almost 70% [18,21], the P3HT PCBM system is at the moment highly optimized. The main limitations in reaching larger power conversion effiden-... 

Recently, the Konarka group achieved power conversion efficiencies of 5.2% for a low band gap polymer-fuUerene bulk heterojunction solar cell, as confirmed by NREL (National Renewable Energy Laboratory, USA). This encourages the practical use of this concept for low cost, large area production of photovoltaic devices. 

The first realizations of polymer-polymer bulk heterojunction solar cells were independently reported in the mid-1990s by Yu and Heeger as well as by Halls et al. [28,30]. These solar cells were prepared from blends of two poly(para-phenylenevinylene) (PPV) derivatives the well-known MEH-PPV (poly[2-methoxy-5-(2 -ethylhexyloxy)-l,4-phenylenevinylene]) was used as donor component, while cyano-PPV (CN-PPV) served as acceptor component (identical to MEH-PPV with an additional cyano (- CN) substitution at the vinylene group). The blends showed increased photocurrent and power conversion efficiency (20-100 times) when compared to the respective single component solar cells. 

In these cases bimolecular recombination limited device efficiencies at higher light intensities nonetheless, up to 1.1% power conversion efficiency was reached under full AM 1.5 solar irradiation [222]. Interestingly, the authors observed an open circuit voltage exceeding the work function difference of the respective electrodes by more than a factor of 2 for various acceptor polymers. The origin of this will be discussed on the basis of polyflu-orene based polymer-polymer solar cells later in this section. 

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