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We investigated and characterized the stability of the power output from methylammonium lead iodide perovskite photovoltaic devices produced with various hole-collecting anode configurations consisting of Au, Ag, MoO x /Au, MoO x /Ag, and MoO x /Al. The unencapsulated devices were operated under constant illumination and constant load conditions in laboratory ambient with periodic current–voltage testing. Although the initial efficiencies of devices were comparable across these configurations, the stability of these devices varied significantly due to subtle differences in the electrode structure. Specifically, we found that devices with MoO x /Al electrodes are more stable than devices with more conventional, and more costly, Au and Ag electrodes. We demonstrate that a thin MoO x layer inhibits decomposition of the perovskite films under illumination in ambient laboratory conditions and greater improvements in device stability are achieved specifically with MoO x /Al electrodes. We investigated the role of the MoO x interlayer in the MoO x /Al electrodes by exploring the effect of relative humidity and the MoO x interlayer thickness on the perovskite solar cell stability.

Solvent additives such as diiodooctane (DIO) are becoming ubiquitous in processing high performance organic photovoltaic (OPV) active layers. Here, we investigate the effects of DIO on the long-term stability of the active layer by studying the photodegradation under ambient white light illumination of the polymer PTB7-Th in pure polymer thin films and in blend films with PC71BM. Using X-ray fluorescence, we directly detect iodine in the active layer films, indicating the presence of residual DIO after casting from solution. Additionally, we show that this residual DIO dramatically decreases the photostability of the active layer. Structural changes in the films upon illumination are probed with grazing-incidence wide-angle X-ray scattering (GIWAXS). FTIR spectroscopy is used to monitor chemical changes in the polymer structure during irradiation in the presence of DIO. Furthermore, we demonstrate that film treatment either with high vacuum (10–8 Torr) for 60 min or with a high-temperature thermal anneal at 175 °C for 30 min removes residual DIO from the film and delays photodegradation. Therefore, when processing polymer solar cells with DIO-containing solutions, it is imperative to remove any trace amounts of DIO from deposited films.

To push perovskite solar cell (PSC) technology toward practical applications, large-area perovskite solar modules with multiple subcells need to be developed by fully scalable deposition approaches. Here, we demonstrate a deposition scheme for perovskite module fabrication with spray coating of a TiO 2 electron transport layer (ETL) and blade coating of both a perovskite absorber layer and a spiro-OMeTAD-based hole transport layer (HTL). The TiO 2 ETL remaining in the interconnection between subcells significantly affects the module performance. Reducing the TiO 2 thickness changes the interconnection contact from a Schottky diode to ohmic behavior. Owing to interconnection resistance reduction, the perovskite modules with a 10 nm TiO 2 layer show enhanced performance mainly associated with an improved fill factor. Finally, we demonstrate a four-cell MA 0.7 FA 0.3 PbI 3 perovskite module with a stabilized power conversion efficiency (PCE) of 15.6% measured from an aperture area of ∼10.36 cm 2 , corresponding to an active-area module PCE of 17.9% with a geometric fill factor of ∼87.3%.

To understand the effects of Ag nanoparticles (NPs) on the performance of organic solar cells, we examined the properties of hybrid poly(3-hexylthiophene):[6,6]-phenyl-C-61-butyric-acid-methyl-ester:Ag NP solar cells using photoinduced charge extraction with a linearly increasing voltage. We find that the addition of Ag NPs into the active layer significantly enhances carrier mobility but decreases the total extracted carrier. Atomic force microscopy shows that the Ag NPs tend to phase segregate from the organic material at high concentrations. This suggests that the enhanced mobility results from carriers traversing Ag NP subnetworks, and that the reduced carrier density results from increased recombination from carriers trapped on the Ag particles. (C) 2011 American Institute of Physics. [doi:10.1063/1.3601742

Interstitial zinc defects in solution-processed ZnO can be mitigated by using a diethylzinc precursor instead of zinc acetate, or by modifying the ZnO surface with a phosphonic acid, resulting in improved organic solar cell stability.

Plastic photovoltaic devices offer a real potential for making solar energy economically viable. Unfortunately, bulk heterojunction (BHJ) solar cells fabricated from blends of the commonly used materials poly(3-hexylthiophene), P3HT, and phenyl-C 61 -butyric acid methyl ester, PCBM, sometimes exhibit low efficiencies even when the procedures followed often produce solar cells with efficiencies exceeding 5%. In this Letter, we show that this irreproducibility is caused by subtleties in the film processing conditions that ultimately lead to poor electron extraction from the devices. For low-performing devices, photogeneration and charge extraction with a linearly increasing voltage ramp (photo-CELIV) measurements show an order-of-magnitude difference in the effective mobilities of the electrons and holes. Atomic force microscopy (AFM) experiments reveal that the top surface of these low-performing devices is nearly pure P3HT. We argue that small variations in the solvent evaporation kinetics during spin-coating of the BHJ active layer, which are difficult to control, cause PCBM to segregate toward the bottom of the P3HT film to different extents, explaining why electron extraction from the PCBM component of the BHJ is so difficult in poorly performing devices. Finally, we show that electron extraction can be greatly improved by spin-coating a thin PCBM layer on top of the BHJ before deposition of the cathode, allowing the reproducible fabrication of high-efficiency polymer solar cells.Organic photovoltaics based on bulk-heterojunction (BHJ) composites of conjugated polymers and fullerenes have shown rapid improvement in the past few years, 1,2 with power conversion efficiencies recently surpassing 6%.3 Although facile, solution-phase fabrication is one of the greatest advantages this class of solar cells has over its inorganic-based counterparts. The behavior of polymer/fullerene devices is sensitive to small variations in processing conditions; 4,5 for example, small changes in material blend ratios, 6 single-percent variations in the composition of the solvent used for spin-coating, 7,8 and changes in postfabrication treatments such as the time and/or temperature of thermal annealing 9 all can dramatically affect device performance. Perhaps even more troublesome, there is not always good reproducibility when different groups use the same processing recipe for producing polymer/fullerene thin-film photovoltaic devices, indicating that there are still processing parameters that we have not yet either correctly identified or properly learned to control in order to consistently optimize device performance.A prime example of this lack of reproducibility can be seen in BHJ devices fabricated from blends of the commonly used materials regioregular poly(3-hexylthiophene), P3HT, and phenyl-C 61 -butyric acid methyl ester, PCBM. BHJ solar cells fabricated from these materials can have power conversion efficiencies (PCEs) exceeding 5%, 9,10 but sometimes, cells fabricated with nominally identical processing conditions can ...

We examine the ultrafast dynamics of exciton migration and polaron production in sequentially processed 'quasi-bilayer' and preblended 'bulk heterojunction' (BHJ) solar cells based on conjugated polymer films that contain the same total amount of fullerene. We find that even though the polaron yields are similar, the dynamics of polaron production are significantly slower in quasi-bilayers than BHJs. We argue that the different polaron production dynamics result from the fact that (1) there is significantly less fullerene inside the polymer in quasi-bilayers than in BHJs and (2) sequential processing yields polymer layers that are significantly more ordered than BHJs. We also argue that thermal annealing improves the performance of quasi-bilayer solar cells not because annealing drives additional fullerene into the polymer but because annealing improves the fullerene crystallinity. All of the results suggest that sequential processing remains a viable alternative for producing polymer/fullerene solar cells with a nanometer-scale architecture that differs from BHJs.