High Efficiency Polymer Solar Cells with Long Operating Lifetimes

Abstract

The power conversion effi ciency of organic photovoltaic (OPV) cells has increased from 4-5% in 2005 [ 1 , 2 ] to 7.4% [ 3 ] and 8.3% [ 4 ] in 2010. The goal of a 10% single junction OPV device seems attainable [ 5 ] making the commercialization of OPV more realistic. With advances made on the effi ciency front, the lifetime and reliability of OPV devices has come into focus. [ 6 , 7 ] To date there has been considerable work done in understanding and quantifying the lifetime and degradation of bulk heterojunction solar cells (BHJs) based on poly( para -phenylene vinylene) (PPV) [8][9][10][11] and poly(3-hexylthiophene) (P3HT) polymers. [12][13][14][15] A comparison of OPV lifetime experimental results across different research groups has posed challenges due to the lack of standardized testing and reporting procedures; however, great strides were made in this regard during the most recent International Summit on OPV Stability (ISOS-3). Modules based on P3HT/fullerene BHJs have shown lifetimes of 5000 h when state-of-the-art encapsulation with a glass-on-glass architecture is used. [ 16 ] Assuming negligible degradation in the dark and 5.5 h of one-sun intensity per day, 365 days per year, this translates into an operating lifetime approaching three years. More recently P3HT/PCBM devices utilizing an inverted architecture have been shown to retain more than 50% of their initial effi ciency after 4700 h of continuous exposure to one-sun intensity at elevated temperatures [ 17 ] and have exhibited a long shelf-life when stored in the dark in ambient conditions. [ 18 , 19 ] However, results to date have yet to show polymer based OPV lifetimes greater than 3-4 years.Here we present a detailed operating lifetime study of encapsulated solar cells comprising poly[9'-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole) (PCDTBT) in BHJ composites with the fullerene derivative [6,6]-phenyl C 70 -butyric acid methyl ester (PC 70 BM). PCDTBT/ PC 70 BM solar cells achieved an effi ciency greater than 6%, [ 20 ] making this one of a small number of polymers able to achieve this level of performance. We describe an experimental set-up that is capable of testing large numbers of solar cells simultaneously, holding each device at its maximum power point while controlling and monitoring the temperature and light intensity. Using this set-up we were able to compare the PCDTBT/PC 70 BM system with the well-studied P3HT/PCBM system and demonstrate a lifetime for PCDTBT devices that approaches 7 years, which is the longest reported operating lifetime for a polymer-based solar cell. Figure 1 shows a typical effi ciency decay pattern for polymer/ fullerene BHJs employing a standard architecture with an organic hole-transporting layer as the anode (e.g., PEDOT:PSS) and a metal cathode (e.g., Ca/Al). [ 14 , 15 ] One typically observes a burn-in period characterized by an exponential loss in effi ciency whose magnitude and duration can vary by polymer system, followed by a linear decay period that someti...

Printable luminescent down shifter for enhancing efficiency and stability of organic photovoltaics

“…For the control device, no UV filtering is present, so this modification occurs rapidly after the commencement of the experiment (t ~ 100 hours). The fall in FF and JSC follows the expected trend with other papers [21], showing a negative exponential drop from t = 0 hour, due to the chemical and physical degradation mechanisms of the photoactive PCBM:P3HT layer and electrode interfaces. T is worth noting, the Voc and FF of OPV with such a device architecture may also degrade under UV-light due to generation of shunts in the ZnO hole blocking layer [15].…”

“…Figure 5 shows how the key performance parameters of VOC, JSC, FF and PCE for the P3HT:PCBM solar cells changed relative to their initial values during light soaking. As expected, the overall performance of devices without encapsulation decreased rapidly with trend matching closely an exponential decay, emphasising the need for encapsulation if devices are to be put to practical use [21,22].…”

Efficient and Air‐Stable Mixed‐Cation Lead Mixed‐Halide Perovskite Solar Cells with n‐Doped Organic Electron Extraction Layers

“…We fit the post "burn-in" section of the power conversion efficiency to a straight line and extrapolate the curve back to zero time to obtain the t = 0 efficiency. We determined the lifetime to 80% degradation (t 80 ) from this t = 0 post burn-in efficiency [63] for the most stable devices to be 656 h, and the SPO is 583 h for the 60 ) and the devices comprising doped C 60 is that the degree of the efficiency drop on burn-in is significantly lower than for the doped cells. The other important observation is that the devices with the doped C 60 layer are persistently more efficient than the devices with the neat C 60 layer over the entire aging window, indicating that the improvement introduced by doping of the C 60 layer is stable.…”

Extended interface layer concept for higher stability and improvement of life time in bulk heterojunction solar cells

“…As such the encapsulation with using glass and epoxy [7][8][9] (along with LiF prior to Al to cathode is being used) is globally utilized for the life time improvement. The device thus encapsulated shows life time improvement 10,11 than the unencapsulated one. However, it is still not adequate for the commercial vibrant.…”