Perovskite Solar Cells with Near 100% Internal Quantum Efficiency Based on Large Single Crystalline Grains and Vertical Bulk Heterojunctions

Abstract

Imperfections in organometal halide perovskite films such as grain boundaries (GBs), defects, and traps detrimentally cause significant nonradiative recombination energy loss and decreased power conversion efficiency (PCE) in solar cells. Here, a simple layer-by-layer fabrication process based on air exposure followed by thermal annealing is reported to grow perovskite films with large, single-crystal grains and vertically oriented GBs. The hole-transport medium Spiro-OMeTAD is then infiltrated into the GBs to form vertically aligned bulk heterojunctions. Due to the space-charge regions in the vicinity of GBs, the nonradiative recombination in GBs is significantly suppressed. The GBs become active carrier collection channels. Thus, the internal quantum efficiencies of the devices approach 100% in the visible spectrum range. The optimized cells yield an average PCE of 16.3 ± 0.9%, comparable to the best solution-processed perovskite devices, establishing them as important alternatives to growing ideal single crystal thin films in the pursuit toward theoretical maximum PCE with industrially realistic processing techniques.

Microstructural Characterisations of Perovskite Solar Cells – From Grains to Interfaces: Techniques, Features, and Challenges

“…[21] For example, TEM-based energy-dispersive X-ray (EDX) has been used to reveal iodine and lead migration in the perovskite layer during thermal treatment, [18b] and EELS has been used to study the organic electron and hole semiconductors in solar cells. [23] However, it should be noted that these inelastic scattering techniques, whether applied in TEM or SEM, necessarily require relatively large electron doses to achieve reliable counting statistics and this can cause severe electron beam damage to the specimen.…”

“…[23] In order to understand the reasons for such excellent charge carrier collection properties, EBIC was used to study the microstructure of the interfaces within the solar [71] Copyright 2014, Nature Publishing Group. c) Line profile of the EBIC current across the grain boundaries between two CH 3 NH 3 PbI 3 grains.…”

“…The grain boundaries filled with SpiroOMeTAD are thus good pathways for allowing holes to travel to the appropriate electrode with reduced resistance. [23] It is clear that elemental and molecular diffusion can readily occur between different layers in perovskite solar cells, and it is therefore important to understand how it happens and what effect it has on the overall performance of the devices. Domanski et al investigated the diffusion of gold from the top contact into the solar cells stack.…”

Nanophase Engineering of Organic Semiconductor-Based Solar Cells

“…Very recently, organometal halide perovskite solar cells have emerged with PCEs rapidly increasing to over 20 % within a very short time [105][106][107][108][109]. The remarkable success of organic-inorganic hybrid perovskites is based upon the combination of the advantages of organic materials, such as low-cost, solution-processing capability, and flexibility, coupled with the advantages of inorganic semiconductors, such as high crystallinity and excellent charge transport properties.…”

A Two‐Resonance Tapping Cavity for an Optimal Light Trapping in Thin‐Film Solar Cells

“…[1][2][3][4] On average, one may estimate that more than 20% of the photons are scattered out of the device or absorbed outside of the active layer. [5][6][7][8] Over decades of thin film technology, many different physical phenomena have been considered and partial success has been reached when a certain degree of light trapping has been demonstrated.…”