Optimized Doping of Diffusion Blocking Layers and Their Impact on the Performance of Perovskite Photovoltaics.

The roll-to-roll printing production process for hybrid organic-inorganic perovskite solar cells (PSCs) demands thick and high-performance solution-based diffusion blocking layers. Inverted (p-i-n) PSCs usually incorporate solution-processed PC70BM as the electron-transporting layer (ETL), which offers good electron charge extraction and passivation of the perovskite active layer grain boundaries. Thick fullerene diffusion blocking layers could benefit the long-term lifetime performance of inverted PSCs. However, the low conductivity of PC70BM significantly limits the thickness of the PC70BM buffer layer for optimized PSC performance. In this work, we show that by applying just enough N-DMBI doping principle, we can maintain the power conversion efficiency (PCE) of inverted PSCs with a thick (200 nm) PC70BM diffusion blocking layer. To better understand the origin of an optimal doping level, we combined the experimental results with simulations adapted to the PSCs reported here. Importantly, just enough 0.3% wt N-DMBI-doped 200 nm PC70BM diffusion blocking layer-based inverted PCSs retain a high thermal stability at 60 °C of up to 1000 h without sacrificing their PCE photovoltaic parameters.

Surface Treatment of Cu:NiOx Hole-Transporting Layer Using ß-Alanine for Hysteresis-Free and Thermally Stable Inverted Perovskite Solar Cells.

Inverted perovskite solar cells (PSCs) using a Cu:NiOx hole transporting layer (HTL) often exhibit stability issues and in some cases J/V hysteresis. In this work, we developed a ß-alanine surface treatment process on Cu:NiOx HTL that provides J/V hysteresis-free, highly efficient, and thermally stable inverted PSCs. The improved device performance due to ß-alanine-treated Cu:NiOx HTL is attributed to the formation of an intimate Cu:NiOx/perovskite interface and reduced charge trap density in the bulk perovskite active layer. The ß-alanine surface treatment process on Cu:NiOx HTL eliminates major thermal degradation mechanisms, providing 40 times increased lifetime performance under accelerated heat lifetime conditions. By using the proposed surface treatment, we report optimized devices with high power conversion efficiency (PCE) (up to 15.51%) and up to 1000 h lifetime under accelerated heat lifetime conditions (60 °C, N2).

Nanoparticulate Metal Oxide Top Electrode Interface Modification Improves the Thermal Stability of Inverted Perovskite Photovoltaics.

Solution processed γ-Fe2O3 nanoparticles via the solvothermal colloidal synthesis in conjunction with ligand-exchange method are used for interface modification of the top electrode in inverted perovskite solar cells. In comparison to more conventional top electrodes such as PC(70)BM/Al and PC(70)BM/AZO/Al, we show that incorporation of a γ-Fe2O3 provides an alternative solution processed top electrode (PC(70)BM/γ-Fe2O3/Al) that not only results in comparable power conversion efficiencies but also improved thermal stability of inverted perovskite photovoltaics. The origin of improved stability of inverted perovskite solar cells incorporating PC(70)BM/ γ-Fe2O3/Al under accelerated heat lifetime conditions is attributed to the acidic surface nature of γ-Fe2O3 and reduced charge trapped density within PC(70)BM/ γ-Fe2O3/Al top electrode interfaces.

Inverted Perovskite Photovoltaics Using Flame Spray Pyrolysis Solution Based CuAlO2/Cu-O Hole-Selective Contact.

We present the functionalization process of a conductive and transparent CuAlO2/Cu-O hole-transporting layer (HTL). The CuAlO2/Cu-O powders were developed by flame spray pyrolysis and their stabilized dispersions were treated by sonication and centrifugation methods. We show that when the supernatant part of the treated CuAlO2/Cu-O dispersions is used for the development of CuAlO2/Cu-O HTLs the corresponding inverted perovskite-based solar cells show improved functionality and power conversion efficiency of up to 16.3% with negligible hysteresis effect.