Abstract:Multijunction solar cells are designed to improve the overlap with the solar spectrum and to minimize losses due to thermalization. Aside from the optimum choice of photoactive materials for the respective sub‐cells, a proper interconnect is essential. This study demonstrates a novel all‐oxide interconnect based on the interface of the high‐work‐function (WF) metal oxide MoOx and low‐WF tin oxide (SnOx). In contrast to typical p‐/n‐type tunnel junctions, both the oxides are n‐type semiconductors with a WF of 5… Show more
“…An example was provided by Bag et al in 2016, where they used an ICL made of evaporated chromium and molybdenum oxide . Only in 2018, Becker et al reported the first all‐oxide ICL for polymer tandem solar cells . A possible reason for the scarcity of such examples might be because very few metal oxide layers guarantee the protection of the front cell active layer against the processing from solution of the back cell active layer .…”
Single-junction solar cells are principally limited in performance by two factors (Figure 1a). Electrons excited by photons with energy higher than the bandgap relax to the band edges, releasing surplus energy as heat (thermalization loss). Photons with energy lower than the bandgap are not absorbed (transmission loss). These losses can be alleviated with two or more absorber layers. The first layer should feature a wide bandgap material to reduce the thermalization loss for high-energy photons. The second layer should have a lower bandgap to absorb the low-energy photons that pass the first layer. In such configuration a tandem cell provides less thermalization and less transmission losses than each of the corresponding single-junction cells. In the detailed-balance limit, a double-junction (tandem) cell can reach an efficiency of 42% and a triple-junction cell 49%. [6] To construct a tandem cell, the two complementary absorber layers must be stacked optically and electrically ( Figure 1b). The interconnecting layer (ICL) between the two subcells must pass light and sustain the photocurrent by providing an optically transparent electrical contact for recombination of electrons and holes from the adjacent photoactive layers. The Fermi level of the hole-transporting layer (HTL) and the electron-transporting layer (ETL) that jointly form the ICL must match the relevant highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels in the adjacent photoactive layers (Figure 1b). The ICL should not cause voltage losses and have low resistance. The open-circuit voltage (V OC ) of the tandem solar cell is ideally the sum of the V OC s of the subcells and the photocurrent is limited by the subcell generating less current. To overcome the intrinsic performance limits of single-junction cells, the subcells should absorb complementary regions of the solar spectrum and generate equal photocurrent.In the first organic tandem solar cells, materials were thermally evaporated. Initially only metal clusters were used to interconnect the subcells, [7][8][9] later complemented by p-and n-doped organic transport layers. [10,11] In 2007, the first fully solution-processed tandem polymer solar cells were reported by Gilot et al. [12] and Kim et al. [13] In both examples the ICL featured a layer of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as HTL, stacked on top of either a zinc oxide or a titanium oxide layer as ETL. Kim et al. achieved a PCE of 6.5%. Since then PCEs have steadily increased. Major improvements involved the use of more efficient photoactive blends that afford a high V OC relative to their optical bandgap The efficiency of organic solar cells can benefit from multijunction device architectures, in which energy losses are substantially reduced. Herein, recent developments in the field of solution-processed multijunction organic solar cells are described. Recently, various strategies have been investigated and implemented to improve the performance of these device...
“…An example was provided by Bag et al in 2016, where they used an ICL made of evaporated chromium and molybdenum oxide . Only in 2018, Becker et al reported the first all‐oxide ICL for polymer tandem solar cells . A possible reason for the scarcity of such examples might be because very few metal oxide layers guarantee the protection of the front cell active layer against the processing from solution of the back cell active layer .…”
Single-junction solar cells are principally limited in performance by two factors (Figure 1a). Electrons excited by photons with energy higher than the bandgap relax to the band edges, releasing surplus energy as heat (thermalization loss). Photons with energy lower than the bandgap are not absorbed (transmission loss). These losses can be alleviated with two or more absorber layers. The first layer should feature a wide bandgap material to reduce the thermalization loss for high-energy photons. The second layer should have a lower bandgap to absorb the low-energy photons that pass the first layer. In such configuration a tandem cell provides less thermalization and less transmission losses than each of the corresponding single-junction cells. In the detailed-balance limit, a double-junction (tandem) cell can reach an efficiency of 42% and a triple-junction cell 49%. [6] To construct a tandem cell, the two complementary absorber layers must be stacked optically and electrically ( Figure 1b). The interconnecting layer (ICL) between the two subcells must pass light and sustain the photocurrent by providing an optically transparent electrical contact for recombination of electrons and holes from the adjacent photoactive layers. The Fermi level of the hole-transporting layer (HTL) and the electron-transporting layer (ETL) that jointly form the ICL must match the relevant highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels in the adjacent photoactive layers (Figure 1b). The ICL should not cause voltage losses and have low resistance. The open-circuit voltage (V OC ) of the tandem solar cell is ideally the sum of the V OC s of the subcells and the photocurrent is limited by the subcell generating less current. To overcome the intrinsic performance limits of single-junction cells, the subcells should absorb complementary regions of the solar spectrum and generate equal photocurrent.In the first organic tandem solar cells, materials were thermally evaporated. Initially only metal clusters were used to interconnect the subcells, [7][8][9] later complemented by p-and n-doped organic transport layers. [10,11] In 2007, the first fully solution-processed tandem polymer solar cells were reported by Gilot et al. [12] and Kim et al. [13] In both examples the ICL featured a layer of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as HTL, stacked on top of either a zinc oxide or a titanium oxide layer as ETL. Kim et al. achieved a PCE of 6.5%. Since then PCEs have steadily increased. Major improvements involved the use of more efficient photoactive blends that afford a high V OC relative to their optical bandgap The efficiency of organic solar cells can benefit from multijunction device architectures, in which energy losses are substantially reduced. Herein, recent developments in the field of solution-processed multijunction organic solar cells are described. Recently, various strategies have been investigated and implemented to improve the performance of these device...
“…Also sol–gel tin oxide has been used for organic photovoltaic devices . Recently, Becker et al presented a tandem polymer solar cell with a molybdenum oxide/tin oxide ICL, where these layers were deposited by thermal evaporation and atomic layer deposition, respectively. Here we demonstrate the use of commercially available tin oxide colloidal dispersions as ETL for the solution‐processing of efficient single junction and tandem polymer solar cells with both the inverted and the conventional configuration.…”
Tin oxide nanoparticles are employed as an electron transporting layer in solution‐processed polymer solar cells. Tin oxide based devices yield excellent performance and can interchangeably be used in conventional and inverted device configurations. In combination with poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a hole transporting layer, tin oxide forms an effective interconnecting layer (ICL) for tandem solar cells. Conventional and inverted tandem cells with this ICL provide efficiencies up to 10.4% in good agreement with optical‐electrical modeling simulations. The critical advantage of tin oxide in an ICL in a conventional tandem structure over the commonly used zinc oxide is that the latter requires the use of a pH‐neutral formulation of PEDOT:PSS to fabricate the ICL, limiting the open‐circuit voltage (VOC) because of its low work function. The SnO2/PEDOT:PSS ICL, on the other hand, provides a nearly loss‐free VOC.
“…In recent years, several different combinations of materials have been proposed as ICL, involving either organic materials or transparent semiconducting metal oxides . For the selective extraction of holes from the photoactive layers poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is widely used but also metal oxides such as MoO 3 , V 2 O 5 , and WO 3 , or graphene oxide (GO) can be used for the purpose.…”
Section: Introductionmentioning
confidence: 99%
“…In recent years, several different combinations of materials have been proposed as ICL, involving either organic materials or transparent semiconducting metal oxides. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] For the selective extraction of holes from the photoactive layers poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is widely used but also metal oxides such as MoO 3 , [25] V 2 O 5 , [26] and WO 3 , [27] or graphene oxide (GO) [28] can be used for the purpose. For selective electron extraction, solution-processed metal oxides such as ZnO nanoparticles, [29] sol-gel TiO x , [11] or Lidoped ZnO [30] are popular.…”
The interconnection layer (ICL) that connects adjacent subcells electrically and optically in solution‐processed multi‐junction polymer solar cells must meet functional requirements in terms of work functions, conductivity, and transparency, but also be compatible with the multiple layer stack in terms of processing and deposition conditions. Using a combination of poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate, diluted in near azeotropic water/n‐propanol dispersions as hole transport layer, and ZnO nanoparticles, dispersed in isoamyl alcohol as electron transport layer, a novel, versatile ICL has been developed for solution‐processed tandem and triple‐junction solar cells in an n‐i‐p architecture. The ICL has been incorporated in six different tandem cells and three different triple‐junction solar cells, employing a range of different polymer‐fullerene photoactive layers. The new ICL provided an essentially lossless contact in each case, without the need of adjusting the formulations or deposition conditions. The approach permitted realizing complex devices in good yields, providing a power conversion efficiency up to 10%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.