More stable hybrid organic solar cells deposited on amorphous Si electron transfer layer

Samiee, Mehran; Modtland, Brian Joseph; Aidarkhanov, Damir; Dalal, Vikram L.

doi:10.1063/1.4878405

Cited by 6 publications

(6 citation statements)

References 16 publications

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“…8 Ultraviolet and blue photons in a full spectrum are known to degrade organic solar cells much more strongly than a LED white light spectrum. 13 Since a use of perovskite cells will be as a top gap cell in a tandem cell arrangement, 14 we examine the photo-degradation of perovskite cells under a full spectrum illumination using an AM1.5 simulator.…”

confidence: 99%

The physics of photon induced degradation of perovskite solar cells

et al. 2016

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Lead-trihalide perovskite solar cells are an important photovoltaic technology. We investigate the effect of light induced degradation on perovskite solar cells. During exposure, the open-circuit voltage (Voc) of the device increases, whereas the short-circuit current (Isc) shows a decrease. The degradation can be completely recovered using thermal annealing in dark. We develop a model based on light induced generation of ions and migration of these ions inside the material to explain the changes in Isc, Voc, capacitance and dark current upon light exposure and post-exposure recovery. There was no change in defect density in the material upon exposure.

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confidence: 99%

The physics of photon induced degradation of perovskite solar cells

et al. 2016

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“…The decrease is likely due to increased trap density. To investigate deep trap defects, the capacitance–frequency C ( f ) technique was used to obtain the DOS and the subgap QE was measured, as described next.…”

Section: Resultsmentioning

confidence: 99%

Carbon Dangling Bonds in Photodegraded Polymer:Fullerene Solar Cells

Fungura

Lindemann

Shinar

et al. 2016

Advanced Energy Materials

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conversion efficiency (PCE), [1][2][3][4][5][6][7][8] up to ≈11.5%, was achieved by, e.g., using low bandgap polymers [1][2][3][4][5][6] and developing approaches to control the active layer's morphology utilizing thermal [7] or solvent annealing, [8] mixed solvents, [4] or additives. [1][2][3][4][5][6] Low bandgap polymers improve the PCE by absorbing more sunlight, increasing the short circuit current density J sc (the value without applied bias). A larger open circuit voltage V oc (the forward bias that zeros the current) is achieved by lowering the polymer's highest occupied molecular orbital (HOMO) energy. [1][2][3][4][5] PSC degradation is the main commercialization obstacle. Hence, extensive efforts are directed at understanding degradation [9][10][11][12][13][14][15][16][17] due to, e.g., moisture and oxygen [9][10][11] and light, [11][12][13][14] although the microscopic nature of the generated defects has not been revealed. This paper demonstrates, for the first time, UV/blue photogeneration of metastable carbon dangling bonds (DBs, i.e., threefold coordinated C atoms) akin to the well-known Si DBs that pervade hydrogenated amorphous Si (a-Si:H). [18] The C DBs are revealed via the electron paramagnetic resonance (EPR) of their unpaired spin 1/2 electron after observing the signature EPR of C DBs at g = 2.0029 ± 0.0004 [19][20][21][22][23] in polymer:fullerene films. Importantly, at room temperature the DBs decay slowly in the dark, in sharp contrast to their stability in a-Si:H. [18] However, since the performance of the solar cells does not recover, it is suspected that the C DBs are passivated by, e.g., O-or OH-related groups, rather than the polymer recovering its original configuration.The paper focuses on low-bandgap polymers of alternating benzo[1,2-b:4,5-b′]dithiophene (BDT) and thieno[3,4-b]-thiophene (TT) units (PBDTTTs), [15] which exhibit PCEs up to 10% for inverted cells in polymer:fullerene bulk heterojunction (BHJ) structures. These polymers have high absorption coefficients up to ≈750 nm and high carrier mobilities. [15,16] Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b] thiophene-)-2-carboxylate-2-6-diyl)] (PBDTTT-EFT; Figure 1) has a HOMO level of −5.24 eV and a lowest unoccupied molecular orbital (LUMO) level of −3.66 eV (i.e., bandgap E g = 1.58 eV; Figure 1). [1] BHJ cells of the related PBDTTT-C:PC 70 BM (phenyl-C 70 -butyric-acid-methyl ester) degrade with heat. [17] To improve stability, understanding the defect states' nature and how they act as trapping/recombination centers is important.Intrinsic photodegradation of organic solar cells, theoretically attributed to CH bond rearrangement/breaking, remains a key commercialization barrier. This work presents, via dark electron paramagnetic resonance (EPR), the first experimental evidence for metastable C dangling bonds (DBs) formed by blue/UV irradiation of polymer:fullerene blend films in nitrogen. The DB density increases with irradiation and decreas...

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“…It is also noted that such defect states are meta-stable in nature and can be recovered with conjunction of appropriate device architecture and post degradation thermal annealing. [9,10,16] There are numerous attempts to eliminate or reduce the amount of photo-degradation which includes the use of in-organic amorphous silicon as electron transport layer (ETL) [17], use of amorphous silicon filter, amorphous silicon-organic (in-organic/organic) tandem solar cells etc. [18,19,20].…”

Section: Introductionmentioning

confidence: 99%

Blue photon management by inhouse grown ZnO:Al cathode for enhanced photostability in polymer solar cells

Bhattacharya

Peer

Joshi

et al. 2018

Solar Energy Materials and Solar Cells

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We report the improvement in photostability of P3HT:PC60BM based bulk heterojunction solar cells deposited on Al-doped ZnO as a cathode layer replacing ITO as regularly used TCO in cells with N-I-P configuration. We experimentally and theoretically demonstrate that use of thicker ZnO:Al as cathode can successfully cut down the rate of photodegradation in short circuit current by ~40% and open circuit voltage by ~30% compared to the control device made on ITO based cathode. This effective reduction in photodegradation is understood to be coming from the absorption of ultraviolet and blue photon in the cathode layer itself. The loss in short circuit current due to the loss of blue photon in EQE is compensated by higher FF (lower series resistance) due to thicker ZnO:Al layer resulting in final device efficiency almost uncompromised with added benefit of reduced photo degradation. The experimental results are supported with optical simulations which show more absorption in the short wavelength region for the thicker ZnO films, compared to ITO films, deposited on glass substrates. This work also proposes using ZnO:Al cathode as a template for random textured front surface to potentially increase short circuit current by increase in photon absorption in active layer matrix by light scattering techniques. Our results provide an inexpensive pathway for improving the stability of organic photovoltaics without compromising the device performance.

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More stable hybrid organic solar cells deposited on amorphous Si electron transfer layer

Cited by 6 publications

References 16 publications

The physics of photon induced degradation of perovskite solar cells

The physics of photon induced degradation of perovskite solar cells

Carbon Dangling Bonds in Photodegraded Polymer:Fullerene Solar Cells

Blue photon management by inhouse grown ZnO:Al cathode for enhanced photostability in polymer solar cells

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