Bulk donor-acceptor heterojunction solar cells

Fig. 3 Contemporary organic solar cell devices are based on donor/acceptor heterojunction device architectures, (a) Energy level diagram, (b) Planar heterojunction conligmation. (c) Bulk heterojunction configuration...

Vandewal K, Tvingstedt K, Gadisa A, Inganas O, Manca JV (2010) Relating the open-circuit voltage to interface molecular properties of donor acceptor bulk heterojunction solar cells. Phys Rev B 81 125204... 

Fig. 5.32. Voc for solar cells using PCBM, azafulleroid 5 and ketolactam 6 as the acceptor component in bulk heterojunction solar cells comprising MDMO-PPV as electron donor...

The observed experimental result that Voc decreases linearly for bulk heterojunction solar cells allows us to conclude that, at least in the high temperature range (T > 200 K), these solar cells may be described by a diode model with Ip exp(E/kT). Here E is a parameter analogous to Eg for conventional semiconductors. For conjugated polymer/fullerene bulk heterojunction solar cells, E should correspond to the energy difference between the HOMO level of the donor and the LUMO level of the acceptor components of the active layer [as also suggested by the extrapolated value of V oc(0 K)]. 

Interpenetrating Network of Donor-Acceptor Organics. Bulk Heterojunction Solar Cells... 

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. 

The ideal schematic structure of a bulk heterojunction solar cell is displayed in Fig. 69. The donor and acceptor phases are interspaced by around... 

The influence of the donor/acceptor ratio on the performance of organic bulk heterojunction solar cells. Presented at the E-MRS spring meeting, Strasbourg... 

H. Zhou, L. Yang, S. Xiao, S. Liu, W. You, Donor-Acceptor Polymers Incorporating Alkylated Dithienylbenzothiadiazole for Bulk Heterojunction Solar Cells Pronounced Effect of Positioning Alkyl Chains. Macromolecules 2010, 43,811-820. 

FIGURE 10.8 The energy diagram of the photoinduced electron transfer and the main energy loss mechanisms in donor-acceptor bulk heterojunction solar cells. 

Jenekhe, Watson, and coworkers [277] reported synthesizing three new donor-acceptor conjugated polymers incorporating thieno[3,4-c]pyrrole-4,6-dione acceptor and dialkoxybithiophene or cyclopentadithiophene donor units. The thieno[3,4-c]pyrrole-4,6-dione acceptor containing materials were studied in bulk heterojunction solar cells and organic field-effect transistors. The polymers had... 

Bulk heterojunction solar cell devices were fabricated by Liu and coworkers, using the copolymers as the electron donor and ([6,6 ]-phenyl-C6i-butyric acid methyl ester) as the electron acceptor. The preliminary research has revealed power conversion efficiencies of 0.17-0.59% under AM 1.5 illumination (100 mW/cm ). 

Similar to organic solar cells, photocurrent generation is a multistep process in NC-polymer hybrid bulk heterojunction solar cells, as demonstrated in Figure 13.7. Briefly, when a photon is absorbed by the absorbing material, electrons are exited from the valance band (VB) to the conduction band (CB) to form excitons. The excitons diffuse to the donor/acceptor interface where charge transfer occurs, leading to the dissociation of the excitons into free electrons and holes. Driven by the... 

Vanderzande et al. reported the facile synthesis to 5,6-disubstituted-l,3-dithienylbenzo[c]thiophenes 3.10 via Pd°-catalyzed coupling reaction of 5,6-dichloroterthiophenes 3.9 with an alkyl Grignard reagent (Scheme 1.30) [309, 321]. Chemical polymerization of the 5,6-modified monomers with FcCIb yielded polymers with bandgaps of 1.4-1.8 eV, which are similar to that of poly(dithienylbenzo[c]thiophene) P3.3 [309]. Application of these polymers as donors and fullerene PCBM as acceptor in bulk heterojunction solar cells (BHJSC) was also investigated and reported. An overall power conversion efficiency of 0.3 % and an internal power conversion efficiency of 24% were obtained for PMMA-poly-P3.9c-PCBM (1 2 6) blended devices [321]. 

Roncali et al. prepared tetrahedral oligothienylsilane derivatives 5.44 and 5.45 by reaction of lithiated terthiophenes with SiCU (Chart 1.72) [486]. In comparison with the linear parent terthiophenes, the tetrahedral structures gave a red shift of 17-19 nm in the absorption spectra. These materials were implemented as the donor component in bilayer heterojunction solar cells, showing a significant increase in performance (jj < 0. 20 %) compared with cells including only the terthiophene branches (t] = 0.04 %) as active material. In bulk-heterojunction solar cells with PCBM as acceptor, 5.45 showed an efficiency of 0.3 %, which is fairly low compared with standard P3HT-PCBM solar cells [195, 196, 487-490]. 

This approach mimics in some way dye sensitized solar cells because porphyrin/fuUerene clusters serve as sensitizers for buffer tin oxide (Sn02). At the same time, mixed fuUerene/polymer nanostructures resemble bulk heterojunction solar cells since donor (porphyrin) and acceptor (fullerene) molecules are blended together in the active layer. 

---