Tianyue Wang

Photo-induced degradation of lead halide perovskite solar cells caused by the hole transport layer/metal electrode interface

Lead halide perovskite solar cells (PSCs) suffer from poor long-term stability, especially due to photo-induced degradation, as PSCs function under continuous sunlight. However, the origins of this instability have not been clearly explored. Herein, the photo-induced degradation of PSCs with mesoporous and planar architectures are investigated, respectively, and the main origin is proved to be correlated with the hole transport material (HTM)/metal (Au) electrode interface. The solar irradiation of PSCs causes significant deterioration of device performance, with the efficiency decreasing from approximately 18% to 2.46% for planar PSCs in 180 min. Electrical analysis of the PSCs and XPS measurements show that the deteriorated performance is induced by retarded carrier extraction from the HTM to the Au electrode, due to a broken interface binding. Accordingly, in situ renewal of the Au electrode was found to cause notable recovery (approximately 80%) of the device performance of both mesoporous and planar PSCs. In comparison, the material degradation of perovskite and the TiO2/perovskite interface were also studied; however, these showed minor effects on the photo-induced degradation of PSCs. These results indicate that the photo-induced degradation of PSCs is mainly caused by the HTM/Au interface. This study provides an important insight into the photo-induced degradation of PSCs, and is crucial for the fabrication of highly photo-stable PSCs.

Dual function interfacial layer for highly efficient and stable lead halide perovskite solar cells

The trap states and the intrinsic nature of polycrystalline organometallic perovskites cause carrier losses in perovskite solar cells (PSCs) through carrier recombination at the surface and subsurface of the perovskites, leading to lowered conversion efficiency. Herein, to reduce the carrier losses, an intelligent approach concerning surface passivation and interfacial doping of the perovskite is proposed by introducing an F4TCNQ interfacial layer. The trap states at the perovskite surface are efficiently suppressed, leading to a homogenous surface potential of perovskite, which avoids the surface carrier recombination. The Fermi level of the perovskite is shifted to its valence band by 0.2 eV, inducing an energy barrier for electron diffusion and contributing directly to a minimized carrier recombination at the subsurface of the perovskite film. Consequently, the performance of the PSCs is remarkably improved, with the average efficiency increased from 14.3 ± 0.9% to 16.4 ± 1.0% (with a maximum efficiency of 18.1%). Moreover, the PSCs with the dual function interfacial layer show enhanced long-term stability in ambient air without device encapsulation.

Degradation of organometallic perovskite solar cells induced by trap states

The degradation of organometallic perovskite solar cells (PSCs) is the key bottleneck hampering their development, which is typically ascribed to the decomposition of perovskite (CH3NH3PbI3). In this work, the degradation of PSCs is observed to be significant, with the decrease in efficiency from 18.2% to 11.5% in ambient air for 7 days. However, no obvious decomposition or structural evolution of the perovskite was observed, except the notable degradation phenomenon of the device. The degradation of PSCs derives from deteriorated photocurrent and fill factor, which are proven to be induced by increased trap states for enlarged carrier recombination in degraded PSCs. The increased trap states in PSCs over storage time are probably induced by the increased defects at the surface of perovskite. The trap states induced degradation provides a physical insight into the degradation mechanisms of PSCs. Moreover, as the investigations were performed on real PSCs instead of individual perovskite films, the finding...

Carrier Step-by-Step Transport Initiated by Precise Defect Distribution Engineering for Efficient Photocatalytic Hydrogen Generation

Semiconductor photocatalysts have been widely used for solar-to-hydrogen conversion; however, efficient photocatalytic hydrogen generation still remains a challenge. To improve the photocatalytic activity, the critical step is the transport of photogenerated carriers from bulk to surface. Here, we report the carrier step-by-step transport (CST) for semiconductor photocatalysts through precise defect engineering. In CST, carriers can fast transport from bulk to shallow traps in the defective subsurface first, and then transfer to the surface active acceptors. The key challenge of initiating CST lies in fine controlling defect distribution in semiconductor photocatalysts to introduce the special band matching between the crystalline bulk and defect-controllable surface, moderate bridgelike shallow traps induced by subsurface defects, and abundant surface active sites induced by surface defects. In our proof-of-concept demonstration, the CST was introduced into typical semiconductor TiO2 assisted by the fluorine-assisted kinetic hydrolysis method, and the designed TiO2 can exhibit the state-of-the-art photocatalytic hydrogen generation rate among anatase TiO2 up to 13.21 mmol h-1 g-1, which is 120 times enhanced compared with crystalline anatase TiO2 under sunlight. The CST initiated by precise defect distribution engineering provides a new sight on greatly improving photocatalytic hydrogen generation performance of semiconductor catalysts.

Research Progress of Solar Cells Based on Organic–Inorganic Hybrid Perovskites Methylamine Lead Halide

Methylamine lead halide is a kind of perovskite structural crystalline materials compounded by organic methylamine and inorganic lead halide, which has attracted great attention in photovoltaic research. Solution processed photovoltaics incorporating methylamine lead halide perovskite absorbers have achieved efficiencies of nearly 16% in solid-state device configurations, superseding traditional dye sensitized solar cells, evaporated and tandem organic solar cells, as well as various thin film photovoltaic. Now, interest has been soaring in this research domain, resulting in more and more controversies that related to the promotion and development of resulting photovoltaic devices. Therefore it is urgent and important to clarify the operating mechanism of such perovskite-based solar cells for their further development. In this rogress Report, we introduced the structure and preparation of organic–inorganic hybrid perovskite methylamine lead halide, and reviewed its latest investigation in solar cell application. Meanwhile, comparative analysis of some different views and key issues such as materials selection, device architecture etc. have been done.

Designing novel thin film polycrystalline solar cells for high efficiency: sandwich CIGS and heterojunction perovskite*

Heterojunction and sandwich architectures are two new-type structures with great potential for solar cells. Specifically, the heterojunction structure possesses the advantages of efficient charge separation but suffers from band offset and large interface recombination; the sandwich configuration is favorable for transferring carriers but requires complex fabrication process. Here, we have designed two thin-film polycrystalline solar cells with novel structures:sandwich CIGS and heterojunction perovskite, referring to the advantages of the architectures of sandwich perovskite (standard) and heterojunction CIGS (standard) solar cells, respectively. A reliable simulation software wxAMPS is used to investigate their inherent characteristics with variation of the thickness and doping density of absorber layer. The results reveal that sandwich CIGS solar cell is able to exhibit an optimized efficiency of 20.7%, which is much higher than the standard heterojunction CIGS structure (18.48%). The heterojunction perovskite solar cell can be more efficient employing thick and doped perovskite films (16.9%) than these typically utilizing thin and weak-doping/intrinsic perovskite films (9.6%). This concept of structure modulation proves to be useful and can be applicable for other solar cells.