Increasing the energy capture efficiency of solar cells with fullerene-derivative interlayers

May 18, 2023

(Nanowerk News) Solar cells are a critical component for the transition to renewable energy sources, and increases in power conversion efficiency (PCE), or the amount of power captured by a given amount of sunlight, increase the practicality of solar power in communities with high energy requirements.

Perovskite solar cells using all-inorganic perovskite light-absorbing materials are more thermally stable than their organic-inorganic hybrid counterparts, but suffer from lower PCE.

Researchers have overcome this hurdle in an all-inorganic perovskite solar cell (PSC) by adding a fullerene-derivative conductive interlayer to improve PCE and thermal stability. Interlayer of bis-dimethylamino-functionalized fullerene derivatives (PCBDMAM) between the electron transport layers of all-inorganic ZnO and CsPbI2.25Mr0.75 perovskite coating of perovskite solar cells improves power conversion efficiency by increasing electron transport. (© Energy Research Nano, Tsinghua University Press)

All-inorganic perovskite solar cells have the advantage of increased thermal stability, which is critical for solar cell longevity, but lack PCE compared to solar cells fabricated with their organic-inorganic hybrid counterparts.

A group of leading materials scientists recently investigated the use of interlayers to repair defects found in inorganic PSCs. In PSCs, layers of perovskite, materials that conduct energy when exposed to light, are prone to morphological problems, energy level mismatch, and electron trapping that decrease electron transport and overall solar cell efficiency.

Introducing a fullerene derived interlayer called a bis-dimethylamino-functionalized fullerene derivative (PCBDMAM), sandwiched between the perovskite and the electron transport layer, overcomes this deficiency, enhancing electron transport and PCE improving temperature stability.

The team published their findings at Nano Research Energy (“Synchronous defect passivation of an all-inorganic perovskite solar cell activated by a fullerene interlayer”).

“High-efficiency PSC devices are mostly based on organic-inorganic hybrid perovskite light-absorbing materials, which are intrinsically volatile and thermally unstable due to the presence of organic cations, resulting in poor thermal stability of PSC devices and hindering large-scale commercialization. Organic-inorganic hybrid PSCs,” said Shangfeng Yang, principal investigator of the study and professor at the CAS Key Laboratory of Materials for Energy Conversion at the China University of Science and Technology in Hefei, China.

“To enhance PSC (all-inorganic perovskite) PCE, interfacial engineering has been widely applied and proven effective in promoting electron transport by improving film morphology, decreasing energy level mismatch, and passivating antisite trapping in perovskite,” Yang said.

“By using various types of interlayers including small molecules, polymers, inorganic compounds, 2D perovskite layers as well as fullerene and their derivatives, passivation of inorganic PSC defects has been achieved,” said Yang.

Specifically, the team used PCBDMAM as an interlayer between the inorganic perovskite layer and the zinc oxide electron transport layer. In this application, PCBDMAM was spin-coated onto the zinc oxide surface as a conductive surface coating to reduce the film morphology and other defects of the inorganic perovskite layer, improve the overall thermal stability of the zinc oxide and perovskite layers and increase the PCE from 15.44% to 17.04%.

A successful transition to renewable energy sources depends, in part, on powerful solar cells that can convert solar energy into electricity efficiently and withstand environmental extremes. Direct recombination, in particular, is a limiting factor in solar cell efficiency and presents a significant challenge for research teams and other materials scientists. Direct recombination is the process in which electrons, created by light in a solar cell, and holes meet each other and recombine. This recombination emits photons, reversing the production of electricity in solar cells.

The research team will continue to overcome hurdles to increase the functionality and lifespan of solar cells to make solar energy production more reliable and less expensive. Future challenges include further mitigation of solar cell defects, including direct recombination, by changing the composition, concentration and application of solar cell coatings to optimize temperature stability and efficiency in a commercially viable and cost-effective way.

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