| The burgeoning field of solar cells has seen many ground-breaking advances in recent years, and it has brought about increasingly more convenience for our daily life thus far. Compared with highly industrial inorganic solar cells, organic polymer solar cells(PSCs) and organic-inorganic perovskite solar cells(pero-SCs) have exhibited distinct advantages such as lower cost, more wide choices in materials, and excellent compatibility with flexible substrates. Therefore, the solar cells have sparked considerable research interest in the past decades. Through a succession of scientific research, the performance of these two kinds of solar cells has been improved gradually. Especially, the power conversion efficiency of pero-SCs has reached 22.1 percent. In order to realize the large-scale application, however, there exist lots of problems that need to be solved. The most serious and urgent problems are the restriction of light absorption in active layer and low mechanical stability of solar cells. This thesis mainly focuses on optimizing the interface of solar cells. The nanostructure has been fabricated to excite local surface plasmon(LSP) mode. The LSP-induced field enhancement has been explored in PSCs to solve the tradeoff between photon absorption efficiency and exciton harvesting efficiency. In addition, by passivating surface defects and modifying the electrode interface, the lifetime of the photo-generated carrier and the mechanical stability of the pero-SCs have been improved. The research results are summarized as follows:(1) Resolving the tradeoff between photon absorption efficiency and exciton harvesting efficiency by using field enhancement of LSP mode to enhance the absorption of active layer in the PSCs.The efficiency of the PSCs was affected directly by the absorption of the active layer. The active layer is generally thin due to the short exciton diffusion length(~10 nm) and low mobility, which could hardly get sufficient light absorption. Thereby, the tradeoff between photon absorption efficiency and exciton harvesting efficiency need to be resolved. Here, we employed the Au-Ag alloy nanoparticles(NPs) into PSCs. LSP resonance peak would be tuned by the composition ratio of Au-Ag alloy nanoparticles. The incorporation of the alloy NPs with an appropriate molar ratio into the PSCs structures supports amplification of the electric field near the particles surface through LSPR and thus results in an enhanced light absorption at the absorption wavelength region of the absorber owing to the near field coupling. The strong scattering of alloy NPs also prolongs the effective optical path propagation in the device. As a result, the short-circuit photocurrent density of the alloy NPs-based PSCs is increased by 18%, and the efficiency of 3.03% is obtained, which corresponds to an enhancement factor of 19%.(2) Enhanced lifetime of photo-generated carrier and thereafter the efficiency of pero-SCs by passivating the surface defects of the perovskite film.Surface morphology of perovskite film is critical for highly efficient perovskite-based solar cells. The solution processed perovskite films tend to have voids and pin-holes between the crystals, which has been cited as very detrimental to device performance. The voids and pin-holes not only cause electrical shorting but also deleteriously impact on charge recombination because of the defects existed on the surface and grain boundaries of the perovskite films. Here we demonstrate passivation of the perovskite surface and grain boundaries by small molecules through infiltration of boron subphthalocyanine chloride(SubPc) into the perovskite film. The defect passivation results in an increased carrier lifetime, which indicates the increased charge diffusion length. Meanwhile, the SubPc infiltration has prevented the harmful contact between the hole layer and the electron transport layer, thereafter reducing the series resistance in the device. As a result, the power conversion efficiency for the solution-processed planar heterojunction solar cells has been enhanced from 9.96% for the contrastive perovskite solar cells to 13.6% for the SubPc passivated perovskite solar cells.(3) An efficient ITO-free flexible pero-SCs with excellent mechanical stability by using continuous ultrathin Au elelctrode.The intrinsic brittleness of the commonly used transparent conducting oxide(TCO) electrodes is one of the limitations for the mechanical stability of the flexible pero-SCs. Metallic films are one of the candidates as the electrode materials in flexible solar cells due to its excellent ductility and conductivity. Ultrathin metallic films could increase the transmittance, but the conductivity and continuity may be reduced. Here we have demonstrated flexible pero-SCs with improved mechanical stability by using ultrathin Au electrode and vapour-deposited perovskite film. The conductivity and continuity of metallic film are governed by the nucleation and the growth kinetics on the substrates, which can be improved by seed layer and modification layer. Meanwhile, perovskite film prepared by vapour deposition has few defects due to small crystals and thermal annealing-free process, which is of significant benefit to the stability of the ultrathin Au electrode-based flexible pero-SCs. The PCE for flexible pero-SCs maintains 74% of their initial efficiencies after 2000 bending cycles with a bending radius of 3.5 mm.(4) Resolving the tradeoff between the transmittance and conductivity by using a dipole resonance coupled with LSP mode which is excited by nanohole array in the metallic film.Metallic film as an ITO alternative, which shows excellent mechanical flexibility and high conductivity, would be a promising electrode for flexible solar cells. However, a bottleneck of metallic film was a lack of transmittance that limits the absorption of the functional layer in solar cells. Here, we have demonstrated a nanoaperture metallic film prepared by adopting the template striping method which can overcome the above mentioned bottleneck. This metallic film has a random nanoaperture arrays. This metallic film with nanoaperture array is not only able to show optical transmittance due to the role of air hole, but also possesses tunable LSP as well. The LSP mode coupled to the dipole resonance in the hole could transmit more radiation into the other side of metallic film, which could largely facilitate the transparent window with strong dispersion and low absorption. The transmittance of the metallic film with nanohole array has a 15% enhancement(@550 nm) and also a high conductivity with low resistance(8.5?/?). Moreover, this metallic film with nanoaperture array will exhibit particular advantage in flexible solar cells, because the backing layer itself is flexible substrate. Thus, this metallic film could be a good electrode for OSCs in the future. |
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