Carbon-based Planar Perovskite Solar Cells Research Articles

Brominated zinc porphyrin assisted grain boundary defects passivation in carbon-based planar perovskite solar cells

Despite the great promotion of perovskite solar cells, the presence of defect trap states at the surfaces and grain boundaries has a negative influence on photovoltaic functionality, primarily due to the polycrystalline nature of perovskite film formation. Motivated by porphyrin molecules excellent charge mobility and various optical transitions in the visible region, we introduce a simple zinc(II)β-tetra-bromo-meso-tetra-phenyl-porphyrin as an additive in the perovskite layer to improve the performance and stability of planar perovskite solar cells. The modified electron density distribution of the molecule developed on electronegative Br sites enables the passivation of charged defect states. Its compatible energy levels and high charge mobility lead to better electron-hole transport through the perovskite layer and defect passivation in the grain boundaries. Moreover, it also has a positive effect on the perovskite film formation quality. As a result, the efficiency of the best device is up to 18.5 %, a factor of 15 % increase to that of the reference cell with a value of 16.1 %, which is superior in planar device structure with copper indium disulfide (CIS) as a hole transport material and carbon as back contact. Furthermore, enhanced hydrophobicity and crystalline quality improve the stability of devices, and the modified device maintained 96 % of its initial efficiency after 40 days in comparison with the control device with 38 % drop in its performance.

Enhanced Efficiency and Stability of Carbon‐Based Perovskite Solar Cells by Eva Interface Engineering

AbstractNanocrystalline tin (IV) oxide (SnO2) as an electron‐transport layer (ETL) has unique advantages in realizing highly efficient and stable planar perovskite solar cells (PSCs), especially showing great potential in the low‐temperature preparation of large‐area flexible carbon‐based PSCs (C‐PSCs). However, the high trap density on the surface of SnO2 tends to cause serious nonradiative recombination losses, thereby reducing photoelectric performance. In this work, an inexpensive and easily obtained polymer poly(ethylene‐co‐vinyl acetate) (Eva) is used as a interfacial modifier to reduce the interfacial defects and nonradiative recombination losses at the SnO2/perovskite interface. As a result, the crystallinity and conductivity of the perovskite layer are significantly increased, and the charge lifetime and stability are effectively improved. The Eva modified SnO2‐based C‐PSCs obtain an optimal power conversion efficiency (PCE) of 12.29%, which is 25.7% higher than that of 9.78% for the unmodified C‐PSCs. Furthermore, the unencapsulated devices maintain 88.6% and 91.9% of the initial PCE over 1 month in ambient air for the unmodified and Eva‐modified C‐PSCs, respectively. The study provides valuable experience for the development of highly efficient and stable C‐PSCs using common polymers for interface modification engineering.

Improving the Efficiency of Hole-Conductor-Free Carbon-Based Planar Perovskite Solar Cells with Long-Term Stability by Using the Hydrazine Acetate Additive via the One-Step Method

Improving the Efficiency of Hole-Conductor-Free Carbon-Based Planar Perovskite Solar Cells with Long-Term Stability by Using the Hydrazine Acetate Additive via the One-Step Method

Controlled Growth of Porous InBr3: PbBr2 Film for Preparation of CsPbBr3 in Carbon-Based Planar Perovskite Solar Cells.

Due to the low solubility of CsBr in organic solvents, the CsPbBr3 film prepared by the multi-step method has holes and insufficient thickness, and the light absorption capacity and current density of the perovskite film hinder the further improvement in the power conversion efficiency (PCE) of CsPbBr3 solar cells. In this study, we introduced InBr3 into the PbBr2 precursor solution and adjusted the concentration of PbBr2, successfully prepared PbBr2 with a porous structure on the compact TiO2 (c-TiO2) substrate to ensure that it fully reacted with CsBr, and obtained the planar carbon-based CsPbBr3 solar cells with high-quality perovskite film. The results reveal that the porous PbBr2 structure and the increasing PbBr2 concentration are beneficial to increase the thickness of the CsPbBr3 films, optimize the surface morphology, and significantly enhance the light absorption capacity. Finally, the PCE of the CsPbBr3 solar cells obtained after conditions optimization was 5.76%.

Investigation of CsPbBr3 films with controllable morphology and its influence on the photovoltaic properties for carbon-based planar perovskite solar cells

Recently, inorganic C s P b B r 3 perovskites have received much research interest in the photovoltaic field owing to their excellent stability. However, it is still challenging to prepare high-performance C s P b B r 3 films with good crystallinity and superior morphology at moderate temperatures. In this work, we report a novel, to the best of our knowledge, multistep spin-coating deposition method to prepare C s P b B r 3 perovskite film. Through optimizing the number of deposition cycles of a CsBr solution, C s P b B r 3 films containing high phase purity, good crystallinity, and strong absorption are obtained. The inorganic planar perovskite solar cell with optimized C s P b B r 3 film realizes a maximum power conversion efficiency of 4.70% under standard solar illumination conditions. Moreover, our devices with F T O / T i O 2 / C s P b B r 3 / C u P c / C exhibit fabulous stability when stored in an ambient atmosphere with ∼ 40 % humidity for 60 days. Our work provides new opportunities for facilitating practical application of C s P b B r 3 planar perovskite solar cells.

High performance carbon-based planar perovskite solar cells by hot-pressing approach

A simple yet effective method based on hot-pressing a free-standing carbon film onto adjacent hole transport layer (HTL) is used to fabricate carbon electrode for planar perovskite solar cells (C–PSCs). Due to the thermoplasticity of as-prepared carbon film, the conductivity of the carbon electrode is enhanced by over ten-fold and the adhesion to adjacent layer is dramatically strengthened via this hot-pressing process. By optimizing the pressing temperature, 15.3% of power conversion efficiency (PCE) is obtained for CuSCN based C–PSCs, which is 70% high than the device without heating at the same pressing pressure. The device demonstrates 93% performance retention after being stored in a humid environment (55–70%) without encapsulation over 80 days. This facile fabrication process of PSCs paves a way to facilitate commercialization of the new PV technology.

Spiro-OMeTAD or CuSCN as a preferable hole transport material for carbon-based planar perovskite solar cells

Carbon electrode-based planar PSCs demonstrated higher device performance and reduced hysteresis using a CuSCN based HTL owing to its favourable energy level alignment with the perovskite compared to conventional spiro-OMeTAD based HTL.

All-inorganic, hole-transporting-layer-free, carbon-based CsPbIBr2 planar perovskite solar cells by a two-step temperature-control annealing process

In this paper, all-inorganic CsPbIBr2 thin films were annealed by a two-step temperature-control process. All-inorganic, hole-transporting-layer-free, carbon-based planar perovskite solar cells (PSCs) with these CsPbIBr2 thin films (FTO/c-TiO2/CsPbIBr2/C) were fabricated. The effect of different first-step annealing temperatures during the two-step temperature-control process (50 °C/280 °C, 80 °C/280 °C, 100 °C/280 °C, 150 °C/280 °C, 180 °C/280 °C) on the photovoltaic conversion efficiency (PCE) of PSCs was investigated for the first time. When the first-step annealing temperature was 150 °C and the second-step annealing temperature was 280 °C, the highest efficiency of 8.31% was obtained. Without encapsulation, the solar cell could retain 97% of the initial PCE, when it was stored at 80 °C and zero humidity for 8 days. For comparison, solar cells with CsPbIBr2 films annealed by a one-step temperature-control process were fabricated. The highest PCE was 4.98%. From this, we could see that there is an increase of 66.9% in PCE, through using a two-step temperature-control annealing process. And also, in order to investigate why the PSCs by a two-step temperature-control annealing process has a higher PCE, all kinds of measurements were done for the first time. According to the results of the measurements, the perovskite film annealed by a two-step temperature-control process has a bigger crystal size, fewer grain boundaries, stronger PL and UV–vis absorption intensities, longer lifetime of minority carriers, less energy loss for hole transporting.

Vapor-assisted deposition of CsPbIBr2 films for highly efficient and stable carbon-based planar perovskite solar cells with superior Voc

CsPbIBr2 perovskite, as a promising light harvester, possesses the most balanced bandgap and stability characters among all-inorganic perovskite materials. However, the poor quality of the traditionally one-step solution-processed CsPbIBr2 film always leads to a severe recombination loss and thus a low output potential difference (Voc). Herein, we demonstrate a novel vapor-assisted deposition strategy to construct high-quality CsPbIBr2 films for the first time, in which the crystallization kinetics of the CsPbIBr2 is more easily controllable than that of the one-step spin-coated one. The PbBr2 film acting as the template in the CsPbIBr2 crystal growth is firstly prepared via an antisolvent-washing technique and CsI is then vacuum evaporated onto the PbBr2 layer. By precisely tuning the thickness of the CsI film, highly phase-pure and crystallized CsPbIBr2 crystals are successfully obtained. The optimized CsPbIBr2 film also exhibits a homogeneous morphology and full coverage over the substrate with large grain sizes up to microscale and ultrahigh light absorption capability. The corresponding carbon-based CsPbIBr2 solar cells achieve a champion power conversion efficiency of 8.76% with a superior Voc of 1.289 V. The large-area (1 cm2) devices also deliver an efficiency of 6.78% with an impressive Voc of 1.336 V. Moreover, under the protection of the highly hydrophobic and chemically stable CuPc layer and carbon counter electrode, the unencapsulated devices present excellent moisture and thermal stabilities. Our work provides a new approach for the preparation of cost-effective, highly efficient and robust CsPbIBr2 photovoltaics.

Sequentially vacuum evaporated high-quality CsPbBr3 films for efficient carbon-based planar heterojunction perovskite solar cells

All-inorganic CsPbBr3 perovskite has triggered great interests in photovoltaic field owing to its superior stability. However, the uncontrollable CsPbBr3 film growth in solution always leads to a poor film quality with low phase-purity as well as many surface and bulk defects. Herein, we demonstrate an environmentally friendly non-solution route to fabricate high-quality CsPbBr3 films for carbon-based planar perovskite solar cells. By precisely tuning the thickness ratio of the evaporated CsBr to PbBr2 precursors (r), the dominant phase conversion of the cesium lead bromide perovskites from PbBr2-rich CsPb2Br5 (r ≤ 12:7) to CsPbBr3 (r = 12:8), and further to CsBr-rich Cs4PbBr6 (r ≥ 12:9) are achieved. The optimized CsPbBr3 perovskites are highly phase-pure and crystallized with ultra-high light absorption ability. The as-prepared CsPbBr3 films also exhibit a dense and uniform morphology with large grain sizes and monolayer-vertical aligned grains. The corresponding devices deliver a champion PCE of 7.58%, which is an excellent efficiency among carbon-based CsPbBr3 cells with evaporated CsPbBr3 light absorbers. The large-area (1 cm2) devices also achieve an efficiency of 6.21%. Moreover, the unencapsulated CsPbBr3 devices present superior moisture and thermal stabilities. Our work provides a facile approach to fabricate high-quality and large-area CsPbBr3 films for highly efficient solar cells, light-emitting diodes and photodetectors.

17.46% efficient and highly stable carbon-based planar perovskite solar cells employing Ni-doped rutile TiO2 as electron transport layer

Organometal trihalide perovskite solar cells (PSCs) with carbon counter electrode (CE) have attracted tremendous interest due to their remarkable properties such as low cost and high stability. However, carbon-based PSCs always suffer from much lower power conversion efficiency (PCE) than the counterparts with noble metal cathode. Herein, we demonstrate a carbon-based planar heterojunction PSC using high-crystallinity Ni-doped rutile TiO2 as electron transport layer (ETL) for the first time, while copper phthalocyanine (CuPc) is introduced as hole transport layer (HTL). It is found that Ni doping can shift the Fermi level of the ETL upward and increase the charge mobility of the TiO2 film, thus enhancing the charge transport and extraction. An optimized PCE of 17.46% was obtained after 0.01 M Ni doping, comparable to or even better than devices with state-of-the-art doped Spiro-OMeTAD as HTL and Au as CE. To the best of our knowledge, this is the highest efficiency that has been reported for carbon-based PSCs. By contrast, the pristine TiO2-based device only displayed a PCE of 15.82%. Detailed superior capability of Ni-doped TiO2 in facilitating charge transfer and suppressing carrier recombination are revealed by Hall effect and photoluminescence (PL) as well as electrochemical impedance spectroscopy (EIS) measurements. Furthermore, the use of highly stable CuPc and commercial carbon makes as-prepared PSCs exhibit excellent stability with no obvious decline in PCE after being stored in ambient air for 1200 h. This work presents an important step forwards to the commercialization of carbon-based PSCs with high efficiency and long-term stability.