This Review summarizes recent progress in the development of polymer solar cells. It covers the scientific origins and basic properties of polymer solar cell technology, material requirements and device operation mechanisms, while also providing a synopsis of major achievements in the field over the past few years. Potential future developments and the applications of this technology are also briefly discussed.

Polymer solar cells

-phenylenevinylene)s L4. Fluorene-Based Conjugated Polymers L4.1. Fluorene-Based Copolymers ContainingElectron-Rich MoietiesM4.2. Fluorene-Based Copolymers ContainingElectron-Deﬁcient MoietiesN4.3. Fluorene-Based Copolymers ContainingPhosphorescent ComplexesQ5. Carbazole-Based Conjugated Polymers R5.1. Poly(2,7-carbazole)-Based Polymers R5.2. Indolo[3,2-

https://ir.nctu.edu.tw:443/bitstream/11536/6508/1/000271856900020.pdf

Synthesis of Conjugated Polymers for Organic Solar Cell Applications

typically based on n-type metal oxides, our device is solutionprocessed at room temperature, enabling easy processibility over a large area. Accordingly, the approach is fully amenable to highthroughput roll-to-roll manufacturing techniques, may be used to fabricate vacuum-deposition-free PSCs of large area, and find practical applications in future mass production. Moreover, our discovery overturns a well-accepted belief (the inferior performance of inverted PSCs) and clearly shows that the characteristics of high performance, improved stability and ease of use can be integrated into a single device, as long as the devices are optimized, both optically and electrically, by means of a meticulously designed device structure. We also anticipate that our findings will catalyse the development of new device structures and may move the efficiency of devices towards the goal of 10% for various material systems. Previously, we reported that PFN can be incorporated into polymer light-emitting devices (PLEDs) to enhance electron injection from high-work-function metals such as aluminium (work function w of 4.3 eV) 22,23 and has thus been used to realize high-efficiency, air-stable PLEDs 24 . Furthermore, we also found that efficient electron injection can be obtained even in the most noble metals with extremely high work functions, such as gold (w ¼ 5.2 eV), by lowering the effective work function (for example lowering w in gold by 1.0 eV), which has previously been ascribed to the formation of a strong interface dipole 25 .

/pdf/enhanced-power-conversion-efficiency-in-polymer-solar-cells-4oh1re6qpi.pdf

Enhanced power-conversion efficiency in polymer solar cells using an inverted device structure

Solution-processed bulk-heterojunction solar cells have gained serious attention during the last few years and are becoming established as one of the future photovoltaic technologies for low-cost power production. This article reviews the highlights of the last few years, and summarizes today's state-of-the-art performance. An outlook is given on relevant future materials and technologies that have the potential to guide this young photovoltaic technology towards the magic 10% regime. A cost model supplements the technical discussions, with practical aspects any photovoltaic technology needs to fulfil, and answers to the question as to whether low module costs can compensate lower lifetimes and performances.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.200801283

Polymer‐Fullerene Bulk‐Heterojunction Solar Cells

Following the development of the bulk heterojunction1 structure, recent years have seen a dramatic improvement in the efficiency of polymer solar cells. Maximizing the open-circuit voltage in a low-bandgap polymer is one of the critical factors towards enabling high-efficiency solar cells. Study of the relation between open-circuit voltage and the energy levels of the donor/acceptor2 in bulk heterojunction polymer solar cells has stimulated interest in modifying the open-circuit voltage by tuning the energy levels of polymers3. Here, we show that the open-circuit voltage of polymer solar cells constructed based on the structure of a low-bandgap polymer, PBDTTT4, can be tuned, step by step, using different functional groups, to achieve values as high as 0.76 V. This increased open-circuit voltage combined with a high short-circuit current density results in a polymer solar cell with a power conversion efficiency as high as 6.77%, as certified by the National Renewable Energy Laboratory. Adding electron-withdrawing groups to the backbone of the polymer PBDTTT is shown to increase the open-circuit voltage of photovoltaic cells, resulting in a polymer solar-cell that has a certified power-conversion efficiency of 6.77%.

/pdf/polymer-solar-cells-with-enhanced-open-circuit-voltage-and-464500qqzd.pdf

Polymer solar cells with enhanced open-circuit voltage and efficiency

Multiple exciton generation (MEG) is a process that can occur in semiconductor nanocrystals, or quantum dots (QDs), whereby absorption of a photon bearing at least twice the bandgap energy produces two or more electron-hole pairs. Here, we report on photocurrent enhancement arising from MEG in lead selenide (PbSe) QD-based solar cells, as manifested by an external quantum efficiency (the spectrally resolved ratio of collected charge carriers to incident photons) that peaked at 114 ± 1% in the best device measured. The associated internal quantum efficiency (corrected for reflection and absorption losses) was 130%. We compare our results with transient absorption measurements of MEG in isolated PbSe QDs and find reasonable agreement. Our findings demonstrate that MEG charge carriers can be collected in suitably designed QD solar cells, providing ample incentive to better understand MEG within isolated and coupled QDs as a research path to enhancing the efficiency of solar light harvesting technologies.

http://science.sciencemag.org/content/sci/334/6062/1530.full.pdf

Peak external photocurrent quantum efficiency exceeding 100% via MEG in a quantum dot solar cell.

Polymer solar cells (PSCs) are commonly composed of a blend film of a conjugated polymer donor and a soluble C60 derivative acceptor sandwiched between an ITO anode and a low-workfunction metal cathode. Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) are the most widely used donor and acceptor materials, respectively. However, the low LUMO energy level of PCBM limits the open circuit voltage (Voc) of the P3HT-based PSCs to ca. 0.6 V. Here we synthesized a new soluble C60 derivative, indene−C60 bisadduct (ICBA), with a LUMO energy level 0.17 eV higher than that of PCBM. The PSC based on P3HT with ICBA as acceptor shows a higher Voc of 0.84 V and higher power conversion efficiency (PCE) of 5.44% under the illumination of AM1.5, 100 mW/cm2, while the PSC based on P3HT/PCBM displays a Voc of 0.58 V and PCE of 3.88% under the same experimental conditions. The results indicate that ICBA is an alternative high-performance acceptor and could be widely used in high-performance ...

Indene−C60 Bisadduct: A New Acceptor for High-Performance Polymer Solar Cells

A new low band gap silole-containing conjugated polymer, PSBTBT, was designed and synthesized. Photovoltaic properties of PSBTBT were initially investigated, and an average power conversion efficiency (PCE) of 4.7% with a best PCE of 5.1% was recorded under illumination (AM 1.5G, 100 mW/cm(2)). The response range of the device covers the whole visible range from 380 to 800 nm. These results indicate that PSBTBT is a promising polymer material for applications in polymer solar cells.

Synthesis, Characterization, and Photovoltaic Properties of a Low Band Gap Polymer Based on Silole-Containing Polythiophenes and 2,1,3-Benzothiadiazole

HOMO level of the PBDTTT-based polymer was successfully reduced by introducing an keton group in place of the ester group. The average PCE of the PBDTTT-based devices reached 6.3% with a champion PCE result of 6.58%. Due to its highly efficient photovoltaic performance and more feasible synthesis approach, PBDTTT-C has the potential to be successfully applied in the large-scale manufacturing of polymer solar cells.

/pdf/synthesis-of-a-low-band-gap-polymer-and-its-application-in-50gbyr0jcj.pdf

Hsiang-Yu Chen

Papers

Polymer solar cells with enhanced open-circuit voltage and efficiency

Peak external photocurrent quantum efficiency exceeding 100% via MEG in a quantum dot solar cell.

Indene−C60 Bisadduct: A New Acceptor for High-Performance Polymer Solar Cells

Synthesis, Characterization, and Photovoltaic Properties of a Low Band Gap Polymer Based on Silole-Containing Polythiophenes and 2,1,3-Benzothiadiazole

Synthesis of a Low Band Gap Polymer and Its Application in Highly Efficient Polymer Solar Cells